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Digitized  by  the  Internet  Archive 

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http://www.archive.org/details/textbookofphysioOOotti 


A  Text-book 


OF 


PHYSIOLOGY 


BY 

Isaac  Ott,  A.M.,  M.D. 

Profkssor  of  Physiology   in  the   Medico-Chirurgical  College   of  Philadelphia; 

Kx-Fellow  in  Bkilogy,.  Johns  Hopkins  University  ;  Consulting  Neurologist, 

NoRRisTOWN   Asylum,   Penna.;  Ex-President   of  American 

Neurological  Association,  etc. 


SECOND  EDITION,  REVISED  AND  ENLARGED 


Illustrated  With  393  Half=Tone  and  Other  Engravings 
Many  in  Colors 


PHILADELPHIA 

F.    A.    DAVIS    COMPANY,    PUBLISHERS 
1907 


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COPYRIGHT,  1904  and  1907, 

BY 

F.   A.   DAVIS  COMPANY. 
[Registered  at  Stationers'  Uall,  London,  Kng.] 


Philadelphia,  Pa.,  U.  S.  A. : 

Press  of  F.  A.  Davis  Company 

19U-1G  Clierry  Street. 


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DEDICATED 

TO    THE    Memory    of    my    Mother 
SARAH  A.   OTT 


PREFACE  TO  THE  SECOND  EDITIOI^, 


The  second  edition  of  tliis  l)oo]%;  has  been  enlarged  by  the  addi- 
tion of  two  hundred  and  forty  pages.  Considerable  new  matter  has 
been  inserted,  for  Physiology  is  a  science  undergoing  continuous 
development. 

The  sul)ject  of  electro-physiology  has  1:»een  treated  more  com- 
prehensively than  in  the  first  edition.  The  article  upon  the  sympa- 
thetic system  has  been  nearly  entirely  re-written.  The  latest  acqui- 
sitions in  this  direction  have  been  incorporated.  The  chapter  on 
Vision  has  Ijeen  entirely  recast.  In  fact,  nearly  every  page  has  l)een 
subjected  to  alterations  and  emendations.  The  work  ujion  peristalsis 
of  intestines  in  the  Medico-Chirurgical  laboratory  has  been  incorpor- 
ated. Over  two  hundred  and  fifty  additional  figures,  many  of  them 
entirely  original,  have  been  included  in  this  edition. 

In  the  chapter  on  Reproduction,  the  first  eleven  pages  and  the 
part  headed  "Evolution"  have  1)een  contril)uted  l)y  Dr.  P.  Fischelis. 
Demonstrator  of,  Histology  and  Eml)ryology,  ]\Iedico-Chirurgical 
College, 

My  cordial  thanks  are  due  to  Dr.  E.  T.  Rehrig  for  the  com- 
plete index. 

Isaac  Ott. 


(V) 


CONTENTS. 


CHAPTER  I.  PAGE 

The   Cell    1 

CHAPTER  II. 
Chemical  Constituents  of  the  Body  and  Food 24 

CHAPTER  III. 
Digestion    45 

CHAPTER  IV. 
ABSORrTION    130 

CHAPTER  V. 

The  Blood 160 

CHAPTER  VI. 

The  Circulation 201 

CHAPTER  VII. 
Respiration .   298 

CHAPTER  VIII. 
Secretion    ; 355 

CHAPTER  IX. 
^rETAHOLTSM     419 

CHAPTER  X. 

Animal  Heat   434 

CHAPTER  XI. 

The  Muscles   456 

CHAPTER  XII. 

Voice  and  Speech  491 

CHAPTER  XIII. 

Electro-phtsiology   ...  503 

CHAPTER  XIV. 

jSTervous  System   534 

(Yii) 


viii  CONTENTS. 

CHAPTER  XV.  PAGE 

Tactilk  Sense   C50 

CHAPTER  X\'l. 
'I\\sTi; G65 

C:iIAPTER  XVII. 

Smelt G70 

CHAPTER  XVI] I. 
Hearing    G77 

CHAPTER  XIX. 
Vision   099 

CHAPTER  XX. 
Cranial  Nerves 748 

CHAPTER  XXL 
REPRODrcTioN    7G9 

Index    • 797 


LIST  OF  ILLUSTRATIOE'S. 


PIG.  PAGE 

1.  Vegetable   Cell.     (Duval) 6 

2.  Cell  with   Reticulum  of  Protoplasm   Radially   Disposed,     p-rom   Intestinal   Epi- 

thelium of  a  Worm.      (Carnoy)    8 

3.  Amceba  Proteus.     (Leidy)    9 

4.  To  Show  the  Changes  in  the  Nerve-coll  Due  to  Age.     (Prom  Howell) 2.3 

5.  Yeast  Fungus.      (After   Harley) 28 

6.  Specimens  of  Milk,   viewed  through  the  Microscope.     (Landois) 40 

7.  Longitudinal  Section  of  a  Molar  Tooth  of  Man.     X  S.     (Sobotta) 51 

8.  Portion  of  the  Crown  of  a  Longitudinal  Section  of  a  Human  Premolar.     X  200. 

(Sobotta)    52 

9.  Portion  of  a  Longitudinal  Section  of  the  Root  of  a  Human  Molar  Tooth.     X  200. 

(Sobotta)    53 

10.  Histology  of  the  Salivary  Glands.     (Landois) 54 

11.  Parotid  of  Cat.      (L.    MOller) G3 

12.  Parotid  of  a  Rabbit  in  Fresh  State.     (Langley) 64 

13.  Human   Stomach.      (After   Sappey) GG 

14.  Vertical  Section  through  the  Gastric  Mucous  Membrane.     (Landois) GT 

15.  Gastric  Contents.     Collective  Microscopic  Picture.     X  350.     (Lenhartz) G9 

IG.  Hourly  Variations  of  the  Secretion  of  Gastric  Juice  in  the  Dog  after  a  Meal  of 

Meat,   Dread,   and   Milk.     (Pawlow) 74 

17.  Hourly  Variations  of  the  Digestive  Power  of  the  Gastric  Juice  in  the  Dog  after 

a  Meal  of  Meat,  Bread,   and  Milk.     (Pawlow,  Gley) 75 

18.  Dog's   Stomach.     (Pawlow)    77 

19.  Dogs  to  whom  a  Fictitious  Meal  is  Given.     They  have  a  fistula  in  the  oesoph- 

agus and  a  fistula  in  the  stomach.  After  a  photograph  taken  in  the  labora- 
tory of  Pawlow.     (Gley) 79 

20.  Portion   of  the  Wall   of  the   Small   Intestine  Laid   Open   to   Show  the  Valvulce 

Conniventes.      (Brinton,    Raymond) SG 

21.  Blood-vessels  of  an  Intestinal  Villus.     (Landois) 87 

22.  Mucous  Membrane  of  the  Jejunum,  Highly  Magnified.     (Schematic.)     (Testut, 

Raymond)    88 

23.  Effect  of  Albumose,  increasing  Peristalsis  92 

24.  The  Pancreas.     (Posterior  View.)     (Bourgery) 93 

25.  Schematic  Section  of  Pancreas.     (Vialleton) 94 

26.  Pancreas  of  Rabbit  Observed  During  Life.     (KOhne  and  Lea) 95 

27.  Hourly  Variations  of  the  Pancreatic  Secretion  after  a  Meal  of  Meat,  Bread,  and 

Milk.     (After  a  curve  obtained  in  the  laboratory  of  Pawlow  by  one  of  his 

pupils,   A.   Walther)    96 

28.  Liver  of   Man.     (Duval) 105 

29.  Diagrammatic  Representation  of  an  Hepatic  Lobule.     (L.\ndois) 107 

30.  Glyeocholic    Acid.      (Duval) 110 

31.  Taurin.     (Duval)    Ill 

32.  Crystals  of   Cholesterin.      (Duval) 113 

33.  Curves   Showing  the  Velocity  of   Secretion  of  Bile  into  the  Duodenum  on    (1) 

a  diet  of  milk,  uppermost  curve;  (2)  a  diet  of  meat,  middle  curve;  (3)  a 
diet  of  bread,  lowest  curve.  The  divisions  on  the  abscissa  represent  inter- 
vals of  thirty  minutes;    the  figures  on  the  ordiuates  represent  the  volume 

of  secretion  in  cubic   centimeters.      (Howell,   after   Bruns) 114 

2i.    A,  Liver-cells  during  fasting.     B,  Cells  filled  with  Glycogen.     (Heidenhain).  .  117 

35.  Aspect  of  an  Intestinal  Loop  before  and  after  Section  of  its  Nerves.     (Armand 

Moreau,   after  Gley) 123 

36.  Stool.      Collective    Microscopic    Picture.      X  350.      (Partly    after    Nothnagel.) 

(Lenhartz)    125 

37.  Inhibitory   Apparatus   of  Ano-spinal   Center 127 

38.  Osmometer.     (Cohen)    133 

39.  A,    Section  of     Villus  of   Rat  killed   during  Fat  Absorption.      (Schafer.)     B, 

Mucous  Membrane  of  Frog's  Intestine  during  Fat  Absorption.     (Schafer).  141 

40.  Lacteals  of  a  Dog  during  Digestion.     (Colin) 143 

41.  The    Superficial    Lymphatics    of    the    Internal    Surface    of    the    Lower    Limb. 

(  Sappey)     144 

42.  Topography  of  the   Thoracic   Duct    (Zuckerhandl.)     (Raymond) 145 

43.  Section  of  Dog's  Intestine,   showing  Villi.      (Cadiat) 149 

44.  Diagram  to  Show  Relation  of  the  Secreting  Cell  of  a  Gland  to  the  Blood  and 

Lymph-supply.      (Starling)     152 

45.  Diminution  of  the  Flow  of  Lymph  under  the  Influence  of  the  Slowing  of  the 

Heart.     Dog  narcotized  with  morphia  and  chloroform.     (L.  Camus) 154 

46.  Dog  with  Medulla  Divided.     (L.   Camus  and  E.   Gley) 155 

47.  Blood-corpuscles  of   Different  Animals.      (Th.^nhoffer) 164 

48.  y4,  Progressive  Pernicious  Amcmiii.    iJ,  Llenal  (Splenic)  Leukieiuia.     <7,  Lien :il  (Splenic) 

Lpukfeniia.     D,  Acute  I.eukiciuin. Facing  164 

49.  Human  and   Amphibian  Blood-corpuscles.     (Landois) 1C5 

50.  Hfemacytometer  of  Thoma-Zeiss.     (Lahousse) 167 

51.  Daland's   Hasmatocrit    1G8 


(ix) 


X  LIST  OF   ILlASTRATrONS. 

Fia.  PAGE 

52.  Uc'd    niood-porpusclps.      (Landois) I(j9 

53.  Leucocytes  of  Man,   showing  Ama?boid   Movement.     (Landois) IT:? 

54.  Blood-plates  and  their   Derivatives.     (Lanuois) 175 

55.  lUood-erystals  of  Man  and  DilTcrent  Animals.     (Thanhoffer  and  Fkey) 17S 

56.  Teichmanii's   IliEmin-erystals.      (Lahousse)    181 

57.  Sorby-Browning   Microspeetroscoix-    182 

58.  Spectra    of     Oxyhccmoglobin,     Ueduced     Haemoglobin,     and     CO     Haemoglobin. 

(Gamgre)     184 

59.  Von    Flcischl    IIa;mometcr.     (Lahousse) 188 

CO.    Relative   Proportion   of   Corpuscles  and  of   Plasma.     (Human   Blood.)     (Lang- 

I.OIS)      189 

CI.  Delicate  Fibrin  Coagulum  (from  Croupous  Pneumonia.)     X  3.50.     (Lenhartz)..  191 

C2.    Anterior  Surface  of  the  Heart.     (Bourgb:ry) 204 

63.  Heart  of  the  Cow,  with  Left  Auricle  and  Ventricle  Laid  Open.     (MOli.er) 205 

64.  Diagram  of  Mammalian  Heart.      (Beclard) .' 206 

65.  Valves  of  Heart   207 

66.  Course  of  Muscular  Fibers  of  Heart.     (Landois) 209 

67.  Course  of  the  Ventricular  Muscular  Fibers.     (Landois) 210 

68.  Diagram  of  the  Circulation.     (Duval) 212 

C9.    A   Cardiac   Cycle.      (Starling) 213 

70.  Sanderson   Cardiograph    216 

71.  Cardiogram   (li)  with  Simultaneous  Record  of     Heart-sounds  (A).     (Hijrthlr, 

Starling)    217 

72.  Magnified   curve   of   the   course   of  pressure   within   the   left   ventricle   and   the 

aorta  of  the  dog,  the  chest  being  open;  to  be  read  from  left  to  right. 
Recorded  simultaneously  by  two  elastic  manometers  with  transmission  by 
liquid.      (Porter)     219 

73.  The  Action  of  the   Semilunar  Valves.     (Chauveau) 222 

74.  The  Action  of  the  Tricuspid  Valve.     (Chauve.\u) 223 

75.  Heart   of   the    Frog.      (Livon) 229 

76.  Schema  of  Ligatures  of  Stannius.     (Hedon) 231 

77.  Cardiac  Plexus  and  Stellate  Ganglion  of  the  Cat.     (Landois) 233 

78.  Course  of  Vagus  fJerve  in  Frog.     (Stirling) 234 

79.  Tracing   by   Lever   Attached   to   Frog's  Heart  on   Stimulation   of  the   Pneumo- 

gastric   Nerve.      (Foster)    235 

SO.    Arrest  of  the   Heart  of   a   Rabbit  by   Irritation   of   the   Peripheral   End  of  the 

Pneumogastric  in  the   Neck.      (Glet) 23C 

81.  Irritation    of    Nervous    Depressor    in    a    Rabbit,    Causing    a    Fall    of    Arterial 

Tension.      (Gley)    237 

82.  Scheme  of  the  Cardiac  Nerves  in  the  Rabbit.     (Landois) 238 

83.  Diagram   of  the   connections  of  the   Depressor  Nerve  in  the   Rabbit  and   Dog, 

according  to  Cyon.  It  will  be  noticed  that  in  the  latter  animal  the 
depressor  nerve  runs  in  the  vagus  trunk  for  the  greater  part  of  the  course. 
(Starling)     2.39 

84.  Schema  of  Innervation  of  the  Heart  of  a  Dog.     (Morat) 240 

85.  Curve  of  Blood-pressure  in  the  Cat,  recorded  by  a  mercury  manometer,  show- 

ing the  increase  in  frequency  of  heart-beat  from  excitation  of  the  aug- 
mentor  nerves.      (From   HoWELL)    241 

86.  Increase   in   the   Force   of   the   Ventricular   Contraction    (curve   of   pressure    in 

right  ventricle)   from  stimulation   of  augmentor  fibers.     (Howell) 242 

87.  Staircase   Contractions  of  a  Frog's  Ventricle   in   Response  to   a  Series  of  like 

Stimuli,  written  on  a  regularly  revolving  drum  by  the  float  of  a  water 
manometer  connected  with  the  chamber  of  the  ventricle.  (Howell,  after 
BOWDITCH)    243 

88.  Refractory  Period  of  Heart-muscle  of  Frog,  with  Compensatory  Pause 244 

89.  To  Illustrate  the  Varying  Excitability  of  the  Frog's  Heart  at  Different  Periods 

of  Systole  and  Diastole.     (Waller) 245 

90.  Weber's  Schema   251 

91.  Marey's   Intermittent  Afflux   Apparatus.      (Lahousse) 254 

92.  Marey's    Sphygmograph.      (Yeo.) 257 

93.  Dudgeon's    Sphygmograph.      (Lahousse) 258 

94.  Sphygmogram   Magnified.      (Lahousse) 259 

95.  Frog's  Web,   Highly  Magnified.     (Yeo,   after  Hlixley) 260 

96.  Showing    the    Relative    Heights    of    Blood-pressure    in    Different    Blood-vessels. 

(Yeo)     263 

97.  Variations   in    Pressure.      (Landois) 264 

98.  Manometer  of  Mercury  for  Measuring  and  Registering  Blood-pressure.     (Yeo).  266 

99.  Ludwig's   Kymograph.      (Yeo) 267 

100.  Blood-pressure  Curve  Recorded  by  the  Mercurial  Manometer.     (Yeo) 268 

101.  Cardiac    Manometer.      (Lahousse) 269 

102.  Riva-Rocci    Sphygmomanometer    270 

103.  Traube-Hering    Curves.      (Fredericque) 272 

104.  Ludwig's    Stromuhr.      (Landois) 275 

105.  Curves  Obtained  by  Enclosing  the  Hind  Limb  of  a  Cat  in  the  Plethysmograph 

and  Stimulating  the  Peripheral  End  of  the  Cut  Sciatic  Nerve  (Bowditch 
and  Warren,   1886).     (Howell) 282 

106.  Effect  of  Irritation  of  the  Splanchnic  Nerve  on  the  Aortic  Pressure.     (Glet)..  283 

107.  Carotid    Pressure    in    Curarized    Dog    after    Section    of    Medulla    .4,    and    after 

Destruction  of  the  Cord  /?.     (Glet) 287 

108.  Elevation   of  Arterial  Pressure  by  Vasoconstriction.     A  result  of  irritation   of 

the  central  end  of  sciatic  in  curarized  dog.     (Hedon) 289 


LIST  OF  ILLUSTRATIONS.  xi 

FIG.  PAGE 

109.  Pick's   Plethysmograph    290 

110.  Stages  iu   Widal   Reartion.     (After  Robin) 293 

111.  Human    Respiratory   Apparatus.      (Duval) 302 

112.  Bronchia  and   Lungs,    Posterior  View.      (Sappey) 303 

113.  Mold  of  a  Terminal  Bronchus  and  a  Group  of  Air-colls  Moderately   Distended 

by  Injection,  from  the  Human  Subject.     (Robin) 305 

114.  Termination  of  a  Bronchus  in  an  Alveolus 306 

115.  Section  of  the  Parenchyma  of  the  Human  Lung,  Injected  Through  the  Pulmo- 

nary   Artery.      (Schulze) 307 

116.  Diagrammatic  Representation  of  the  Action  of  the  Diaphragm.     (Beclard).  .. .  309 

117.  The  Action  of  the  Ribs  in  Man  in  Inspiration.     (Beclard) 310 

118.  Schema  of  Respiratory  Mechanism  in  Inspiration.     (Laulanie) 311 

119.  Schema  of  Respiratory   Mechanism  iu  Expiration.     (Laulanie) 312 

120.  Schema  of  Action  of  Intercostal  Muscles.     (Landois) 313 

121.  Tracing  of  a     Respiratory   Movement.     (Foster) 315 

122.  Marey's  Tympanum  and  Lever.     (Sanderson) 316 

123.  Spirometer.     (Fredericque)    317 

124.  Gad's    Aeroplethysmograph.      (Krusich)    320 

125.  Number  of  Respirations  by  Man  at  Different  Ages.     (Quetelet) 321 

126.  Carotid  Pressure  in  Dog.     Acceleration  of  Heart  at  the  Moment  of  Inspiration 

is  Well  Marked.     (Langlois) 322 

127.  Apparatus   to    Illustrate    Relations    of    Intra-thoracic    and    External    Pressures. 

(After    Beaunis) 323 

128.  Illustrating  Atmospheric  Pressure  During  Respiration 324 

129.  Comparison    of   Blood-pressure    Curve   with   Curve   of   Intra-thoracic    Pressure. 

(M.  Foster)     324 

130.  Illustrating  Arterial   Blood-pressure   During  Respiration 325 

131.  Illustrating   Venous   Blood-pressure    During    Respiration 326 

132.  Rabbit  (morphine  gr.   Vn  injected  hypo.).     (Dr.   W.   H.   Good) 330 

133.  Scheme  of  the  Chief  Respiratory  Nerves.     (Landois,  after  Rutherford) 331 

134.  Arrest  of  Respiration  in  State  of  Expiration.     (Hedon) 332 

135.  Apparatus   for   Taking   Tracings   of   the   Movements   of  the   Column   of   Air   in 

Respiration.      (Foster)     334 

136.  Shows  the  Position  to  be  Adopted  for  Effecting  Artificial  Respiration  in  Cases 

of   Drowning.      (Schaefer,    Howell) 3.37 

137.  Cheyne-Stokes   Respiration.      (Waller)    340 

138.  Ludwig's  Mercurial  Air  Pump  to  Extract  Blood  Cases.     (Lahousse) 341 

139.  Schema  of  the  Large  Respiration  Apparatus  of  Pettenkofer.     (Fredericque)..  342 

140.  Showing  Constituents  of  Air  Inspired  and  Expired.     (Langlois) 343 

141.  Variations  of  Respiratory  Quotient  According  to  Food  Taken.     (L.\nglois).  .. .  345 

142.  Variations  of  Respiratory  Quotient  According  to  the  Food  Taken.     (Langlois).  346 

143.  Relative  Proportion  of  Gases  of  Blood.     (Langlois) 347 

144.  Structure  of  the  Thyroid  (Morat  and  Doyon).     Lobule  of  the  Thyroid  after  an 

Injection  of  the  Lymphatic  Vessels  with  Nitrate  of  Silver.     Semi-schematic. 
(Vialleton)    358 

145.  Parathyroid  of  Dog   (Morat  and   Doyon).      (Vialleton) 359 

146.  Illustrating   Nicholson's   Article   on   Thyroid   Treatment  in   a   Cretin    (Arch,   of 

Ped.,   .June,   1900).     (Raymond) 360 

147.  Effect  of  lodothyrin  on   Intestinal   Peristalsis 363 

148.  Effect  of  Extract  of  Spleen  on  Intestinal  Peristalsis 365 

149.  Adrenal  Capsules  of  a  Rabbit.     (Morat  and  Doyon) 365 

150.  Section   of  Adrenal.      (Vialleton) 360 

151.  Effect  of  Adrenalin  on  the  Volume  of  Inspired  and  Expired  Air.     Tracing  with 

Gad's   Aeroplethysmograph    3G7 

152.  Effect  of  Adrenalin  on   Intestinal   Peristalsis 368 

153.  Cat.     One  drop  of  adrenalin   solution  and  ten  drops  of  1-per-cent.   solution  of 

nitroglycerin,  mixed  and  then  injected  per  jugular 368 

154.  Turtle  Heart,   Suspended   by  Lever 369 

155.  Effect  of  Suprarenal  Extract  upon  Muscle-contraction  in  the  Frog.    (Schafer).  370 

156.  Mammary  Gland  of  Human  Female.     (After  Liegeois) 373 

157.  Dog's  Mammary  Gland  in  First  Stage  of  Secretion.     (Heidenhain) 375 

158.  Mammary  Gland  of  the  Dog,  Second  Stage  of  Secretion.     (Heidenhain) 376 

159.  Sweat  Gland.      (Hedon) 377 

160.  Section  of  Sweat-glands  of  Cat  379 

161.  Relations  of  the  Kidnev.     (After   Sappey) 384 

162.  Section  of  Kidney.      (Landois) 386 

163.  Diagram  of  the  Course  of  Two  Uriniferous  Tubules.     (Landois) 3S'7 

164.  Structures  of  Kidney.     (Landois)    388 

165.  Longitudinal   Section   of   a   Malpighian   Pyramid.      (Landois) 389 

166.  Blood-vessels   and   Uriniferous  Tubules  of   the   Kidneys.      (Semidiagrammatic.) 

(Landois)    390 

167.  Urea  from  Human  Urine.     (Funke) 395 

168.  Micrococcus  Ureae.     X  500.     (After  von  Jaksch) 396 

169.  Uric-acid  Crystals  with  Amorphous  Urates.     (Purdy,  after  Peyer) 398 

170.  Uric  Acid.   Effect  of  on   Intestinal   Peristalsis 399 

171.  Urate  of  Soda  and  Crystals  of  Uric  Acid  (h).  Oxalate  of  Lime  (o),  and  Cystin 

(r).      X  350.      (Lenhartz)    400 

172.  Effect  of  Xanthin  on  Muscle  Curve,  Causing  an  Extra  Contraction  during  the 

Relaxation.     (J.   F.  Ulman) 402 

173.  Leucin  in  Balls;    Tyrosin  in  Sheaves.     (Peter) 403 

174.  Crystals  of  Ammonio-magneslum  Phosphate.     (After  Ultzmann) 408 


xii  LIST  OF   ILLUSTRATIONS. 

FIG.  PAOE 

175.  Feathery  Crystals  of  Triple  Phosphate.     X  350.     (After  Tyson) 409 

17G.  Crystals  of  PhenylKlucosazono.     (I'URDY,   after  v.   Jak.scii) 412 

177.  Blood-pressure  ami    Volume  of   Kidney.     (STiiu.lNn,   after  Roy) 414 

178.  Diagram,   of    Nerve-supply    to    Itladder.      (Nawkocki,    Skabitchewsky,    and 

Starling)    417 

179.  Variations    in    the    Bodily    Temperature    during    Health    within    Twenty-four 

Hours.      (Landois)    438 

180.  Human   Calorimeter    442 

181.  Bilateral  Puueture  of  the  Tuber  Cineroum  of  Rabbit  Through  Roof  of  Mouth..  445 

182.  Puncture  of  Tuber  Cinereum  in  Rabbit,   Showing  Effect  on  Respiration,  Arte- 

rial  Tension,   Pulse,   and   Temperature 44G 

183.  Cortex  of   Cat's   Brain    418 

184.  Lesions  of  Cortex  in   Man,  Causing  Elevations  of  Temperature 449 

185.  Curves    of    Temperature    and    Respiration    when    Cortex    is    Removed    and    the 

Animal    is   Artificially    Heated    '. 450 

186.  Curve  of  Temperature  and  Respiration  when  the  Tuber  Cinereum  is  Destroyed 

and  the  Animal   is  Artificially  Heated   451 

187.  Heat  Production  and  Heat  Dissipation  in  Man  during  a  Paroxysm  of  Malarial 

Fever— a  Great  Increase  of  Heat  Production 453 

188.  Histology  of  Muscular  Tissue.     (Ellenberger) 459 

189.  Unstriped   Muscular   Tissue.      (Ellenberger)    40.') 

190.  The  Pendulum  Myograph.     (Foster) 473 

191.  A  Muscle-curve  Obtained  by  Means  of  the  Pendulum  Myograph.     (Foster) 475 

192.  Arrangement  of  Apparatus  in  Conducting  Experiments  on  Nerve  and  Muscle. 

(Stirling)     476 

193.  Fatigue-curves   of  Frog's  Muscle.      (Waller) 477 

194.  Effect   of    Increase    of    Current   on    Efficiency    of    Breaking    Induction    Shocks. 

(Howell,   after  Fick)    477 

195.  An   Experiment  to  Show  that  a  Contracting  Muscle  does  not  Change  its  Vol- 

ume.     (Hedon)    478 

19G.    Apparatus  for  Measuring  the  Velocity  of  the  Wave  of  Muscular  Contractions. 

(Marey)    479 

197.  Rate  of  Conduction  of  the  Contraction  Process  along  a  Muscle  as  shown  by  the 

Difference  in  the  time  of  Thickening  of  the  two  Extremities.  (Marey, 
Howell)     480 

198.  Tracing  of  a  Double  Muscle-curve.      (Foster) 480 

199.  Progress  in  Fusion  of  Contraction.     (Laulanie) 481 

200.  1.  Imperfect  Tetanus,   15  Contractions  per  second.     2.  Perfect  Tetanus.     (Lau- 

lanie)      482 

201.  Extensibility  of  Elastic  Band  and  Muscle.     (Waller) 484 

202.  Extensibility  of  Muscle  in  Various  States.     (Waller) 485 

203.  Mosso's   Ergograph   487 

204.  Ergographic  Curves.     (After  Mosso) 488 

205.  Ergographic  Curve  of  a  Case  of  Addison's  Disease,  Showing  Rapid  Exhaustion 

of  Muscle.     (Langlois)    489 

206.  Fick's  Work  Adder.     (Laulanie) 489 

207.  Curve  of  Contraction  of  the  Unstriped  Muscle  of  Miiller  in  Dog.     (Laulanie)..  490 

208.  The  Larynx  as  Seen  with  the  Laryngoscope.     (Landois) 492 

209.  Action  of  the  Muscles  of  the  Larynx.     (Beaunis) 493 

210.  Schematic  Horizontal  Section  of  Larynx.     (Landois) 494 

211.  Schematic  Closure  of  the  Glottis  by  the  Thyro-arytenoid  Muscles.     (Landois).  495 

212.  The   Posterior   Rhinoscopic   Image.      (Bosworth) 497 

213.  Position  of  Vocal  Cords  on  Uttering  a  High  Note.     (Landois) 498 

214.  Daniell   Cell    504 

215.  DuBols  Nonpolarizable  Electrodes.      (Lahousse) 507 

216.  Tetanizing  Key  of  DuBois-Reymond.     (After  Rosenthal) 508 

217.  Pohl's  Commutator.     (Lahousse)   509 

218.  DuBois-Reymond's  Induction   Apparatus.      (Waller) 511 

219.  Principle   of   Simple   Rheocord 512 

220.  Schema  of  Apparatus  to  Study  Influence  of  Rapid  Variations  of  the  Constant 

Current  by  the  Rheonome  of  von  Fleischl.     (Lahousse) 513 

221.  Schema  of  Experiment  to  Measure  the  Rapidity  of  the  Muscle  Current  by  the 

Aid  of  the  Differential   Rheotome  of  Bernstein.     (Lahousse) 514 

222.  The  Nerve-muscle  Preparation.     (Stirling) 515 

223.  Thompson    Galvanometer    516 

224.  Diagram  of  Capillary  Electrometer.      (Starling) 517 

225.  Direction  of   Current  of   Daniell   Cell 518 

226.  Direction  of  Current  of  Injured  Muscle.     (Waller) 518 

227.  Schema  Representing  the  Inequalities  of  Electric  Tensions  upon   the  Natural 

Longitudinal  Surface  and  upon  the  Artificial  Transverse  Surface  of  a 
Muscle-cylinder.  Also  the  direction  of  the  electric  currents  from  the 
exterior  to  the  interior  of  the  muscle.     (Lahousse) 519 

228.  The  Negative   Variation    (Frog's   Gastrocnemius).      (Waller) 520 

229.  Arrangement    of    Parts    to    Show    Secondary    Contraction    in    Muscle.      (After 

Rosenthal)     521 

230.  Effect    of    Chloroform     upon    the    Electrical     Responses    of     Isolated     Nerve. 

(Waller)    522 

231.  The  Structure  of  Nervous  Tissue.     (Landois) 525 

232.  Cells  from  Anterior  Horn  of  Human  Spinal  Cord.     Ganglion  Cells.     (Ramon  t 

Cajal.)     Neuroglia.      (Weigert)    526 


LIST  OF  ILLUSTRATIONS.  xiii 

FIG.  PAGE 

233.  Ganglion    Cell   from    Sympathetic    Ganglion   of   Frog;     Greatly   Magnified,    and 

Showing  Both  Straight  and  Coiled  Fibers.     (After  Quain) 527 

234.  A  Piece  of  MeduUated  Nerve-fibril  of  Man,  Nucleus  and  Axis  Cylinder  Stained 

by  Carmine.     (Sobotta)    52y 

235.  A  Piece  of  MeduUated  Nerve  of  Man.     It  shows   Ranvier's   Constrictions   and 

Lantermanu's   Incisures.      (Sobotta)    529 

236.  Two   Nerve-pairs  at  Their  Origin   in   the   Spinal   Cord — Anterior  and   Posterior 

Roots.      (MORAT)    540 

237.  Transverse  Section  of  the  Spinal  Cord 546 

238.  Section  of  Spinal  Cord,  Showing  the  Less  Well-known  Tracts 549 

239.  Medulla  Oblongata,   Pons,   Cerebellum,   and  Pes  Pedunculi.     Anterior  View,   to 

Demonstrate   E.xits  of  Cranial   Nerves.      (Edinger) 551 

240.  The  Three  Pairs  of  Cerebellar  Peduncles.    (After  Hirschfeld  and  Leveille).  552 

241.  Metencephalon,   Mesencephalon,   and  Thalamencephalon,   from  the  Dorsal  Sur- 

face.     (Gordinier,    after   Obersteiner) 554 

242.  Diagrammatic  Transverse  Section  of  the  Spinal  Bulb  X  3,  at  about  the  middle 

of  the   olivary   body,    to   illustrate  the   principal   nuclei   and   tracts   at  that 
level.      (Waller,   after   Schwalbe) 555 

243.  Cross-section    of    the    Oblongata    through    the    Decussation    of    the    Pyramids. 

(After  Henle) 556 

244.  Section  of  Medulla  Oblongata  at  the  Level  of  the  Decussation  of  the  Pyramids 

—Motor  Decussation.     (M.    Duval.)     Section   of  Medulla   Oblongata  at  the 
Upper  Part — Sensory  or  Fillet  Decussation.     (M.   Duval) 558 

245.  The  Base  of  the  Brain.     The  Left  Lobus  Temporalis  is  in  Part  Represented  as 

Transparent  in  Order  that  the  Entire  Course  of  the  Optic  Tract  Might  be 
Seen.      (Edinger)    561 

246.  Diagram  to  Illustrate  Some  of  the  Connections  of  the  Nuclei  of  the  Nerves  to 

the   Ocular   Muscles.     (Starling,   after  Held) 563 

247.  Diagrammatic  Transverse  Section  Through  the  Crus  Cerebri  and  Anterior  Cor- 

pora Quadrigemina.     (Waller,   after  Obersteiner) 564 

248.  Section  of  the  Crus  Cerebri.     (Morat) 565 

249.  The  Mesial  Fillet,   Ending  Chiefly  in  the  Ventral  Nucleus  of  the  Optic  Thala- 

mus and  then  United  by  New  Neuraxons  (Upper  P^illet)  to  Parietal  Cortex..  5G8 

250.  View  from  the  Side  and  Slightly  from  Above  and  Behind  of  the  Right  Hemi- 

sphere of  a  Simply  Convoluted  European  Brain.     (Quain) 569 

251.  Lateral  Aspect  of  Brain.     (Edinger) 571 

252.  Mesial  Aspect  of  Left  Hemisphere  of  a  European  Brain.     (Quain) 572 

253.  Longitudinal   Section   Through   the   Middle   of  an   Adult   Brain.     The   posterior 

portion   of   the   thalamus,    the   crura   cerebri,    etc.,    have   been    removed,    in 
order  to  expose  the  inner  surface  of  the  temporal  lobe.     (Edinger) 573 

254.  Section  Through  the  Cerebral  Cortex  of  a  Mammal.     (Edinger  and  Cajal)...  574 

255.  The    Brain-structures    from    the    Thalamus    to    the    Spinal    Cord    (the    "Brain- 

stem").    (Edinger)    575 

256.  Thalamus  and  Corpora  Quadrigemina  Seen  from  the  Side.     (Edinger) 576 

257.  Median   Sagittal   Section  Through  the  Interbrain  and  the  Structures  Posterior 

to  it.     (Edinger)    577 

258.  Median  Section  of  the  Brain.     (Quain) 579 

259.  So-called   Ganglionic   Gray   Matter   of   the   Cerebral    Trunk.      (After   Charpy.) 

Gray  Masses  Superadded  to  the  Scnsori-motor  Nuclei.     (Morat) 580 

260.  Ideal   Horizontal   Section   Through   the    Right   Hemisphere   and   Basal   Ganglia. 

(Waller,   after  Charcot)    581 

261.  Internal   Capsule.     (Sherrington)    582 

262.  Motor   Tract.      (Morat)    583 

263.  Sensory  Tract.     (Morat)   585 

264.  D,   Dubois-Reymond's  Spring  Myograph  to  Measure  the  Rapidity  of  the  Nerve 

Current  in  Motor  Nerves.     (Lahousse) 589 

265.  Curves   Illustrating   the   Measurement   of   the   Velocity   of   a    Nervous   Impulse 

(Diagrammatic).      (Poster)    590 

266.  Method  of  Studying  Physiological   Electrotonus.     (Lahousse) 592 

267.  Schema  of  Apparatus  for  the  Study  of  the  Law  of  Contractions  in  the  Frog. 

(Lahousse)    593 

268.  Scheme    of    Electrotonic    Excitability 594 

269.  Pfliigor's  Law  of  Contraction  of  Nerve-muscle  Preparation 595 

270.  Anelectrontonic      Current.        Polarizing      Current.        Katelectrotonic      Current. 

(Waller)    598 

271.  Elementary  Reflex  Arc.     Course  of  Senscu-y  Injpressions  and  a  Motor  Impulse, 

Passing  Through  the  same  Level  of  tne  Spinal  Cord.     (Morat) 599 

272.  Diagram  of  the  Roots  of  a  Spinal  Nerve,  Showing  Effect  of  Section.    (Landois).  604 

273.  Floor  of  Fourth  Ventricle  of  Rabbit.     (Hedon) 611 

274.  Horizontal  Section  Through  the  Cerebellum.     (After  B.  Stilling) 613 

275.  Section  of  Cerebellum  of  Man  Treated  by  Golgi  Method.     (Sobotta) 615 

276.  Schema  Showing  the  Origin  and  Course  of  the  Fibers  of  the  Peduncles  of  the 

Cerebellum.      (Edinger)    616 

277.  Connections  of  the  Cerebellum  with  Cerebrum,  Pons,  and  Spinal  Cord.    (Schema 

of  Charpy.)     (Morat)    618 

278.  Effects  of  Removal  of  Cerebellum.     (Dalton) 619 

279.  The  Motor  Area  and  its  Subdivisions  on  the  Lateral  Aspect  of  the  Hemicere- 

brum  of  the  Chimpanzee.     (Grunbaum  and  Sherrington) C24 

280.  The  Motor  Areas  and  Centers  on   the  Mesial   Aspect  of  the  Hemicerebrum  of 

the  Chimpanzee.     (GrOnbaum   and   Sherrington) 625 


xiv  L1«T  OF  ILLUSTRATIONS. 

FIG.  PAGE 

281.  Areas    and    Centers    of    the    Lateral    Aspect    of    the    Human    Ilemicerebrum. 

(Mills)    C26 

282.  Areas    and    Centers    of    the    Mesial    Aspect    of    the    Human    Hemicerebrum. 

( M ILLS)    627 

283.  Lateral    View  of   a  Human   Hemisphere,    Showing   the   Bundles   of  Association 

Fibers.      (Stakr)    630 

284.  Effects  of  Ablation  of  Cerebrum.     (Dalton) 63^ 

285.  Curve  of  the  Depth  of  Sleep.     (Piesbergen) 635 

2S6.     Pyramidal  Cells  of  the  Marmot  In  Two  Different  Conditions.     (After  Querton).  636 

287.  Diagram   of  the   Origin,   in   Man,    of   the   Efferent  Autonomic   Fibers   from   the- 

Central   Nervous   System.     (Langley) 640 

288.  Gungli.'i  and  Fibers.     (Langley)     641 

289.  Diagram    of    the    Main    Distribution    of    the    Bulbar    and    Sacral    Autonomic 

Fibers.      (Langley)    642 

200.     Diagram    of    the    Great    Sympathetic,    Representing    its    Viscecal    Distribution. 

(Morat)    (i-l^ 

291.  Diagram   of   the    Great   Sympathetic,    Representing   its   Cutaneous    Distribution 

and  its  Two  Orders  of  Fibers  of  Projection C44 

292.  An  Afferent  Sympathetic   Fiber   615 

293.  Efferent   Sympathetic    Fiber    646 

294.  Cross-section    of    Neurotendinous    Nerve    End-organ    of    Rabbit    from    Tissue 

Stained   in   Methylene   Blue.     (Huber  and   Dewitt) 652 

295.  Histology  of  the  Skin  and  the  Epidermoidal  Structures.     (Landois) 654 

296.  Cutaneous    Papilla;    Deprived    of    Their    Epidermis    and    the    Vessels    Injected. 

(Landois)    656 

297.  Vater-Pacinian  Corpuscle  from  the  Mesentery  of  the  Cat,  Fixed  in  a  Platinum 

Chlorid-osmic  Acid  Solution.     X  45.     (Sobotta) 657 

298.  Krause's   Corpuscle.      (Hedon)    658 

299.  Transverse  Section  of  Two  Grandry's  Corpuscles  from  the  Tongue  of  a  Duck. 

X  450.      (Sobotta) 659 

300.  Topography  of  Sensibility  to  Cold  and  Heat  in  the  same  Region  of  the  Ante- 

rior Surface  of  the  Thigh.     (Goldschbider,  Hedon) 661 

301.  Structure  of  the  Taste-organs.     (Landois)   667 

302.  Sternberg's  Gustometer   668 

303     Innervation  of  the  External  Wall  of  the  Nasal  Fossa.     (Testut) 670 

304.  Internal   Structure   of   Nose.      (Bishop) 671 

305.  Diagram    of    the    Connections    of    Cells    and    Fibers    in    the    Olfactory    Bulb. 

(Schafer,   in   Quain's  Anatomy)    672 

306.  Zwaardemaker's    Olfactometer    675 

307.  Diagram  of  the  External  Surface  of  the  Left  Tympanic  Membrane.     (Hensen).  678 

308.  Tympanic  Membrane  and  Auditory   Ossicles,   seen   from  the  Tympanic"  Cavity. 

(Landois)    679 

309.  Left  Tympanum  and  Auditory  Ossicles.      (Landois) 680 

310.  Scheme  of  the  Organ  of  Hearing.     (Landois) 681 

311.  Scheme  of  the  Labyrinth  and  Terminations  of  the  Auditory  Nerve.     (Landois).  683 

312.  Section    through   the    Uncoiled    Cochlea    (I)    and    through    the    Terminal    Nerve 

Apparatus  of  the  Cochlea  (II).     (Munk,  after  Hensen) 684 

313.  Section  of  the  Ductus  Cochlearis  and  the  Organ  of  Corti.     (After  Landois) 685 

314.  Connections  of  Cochlea  with  Central  Nervous  System.     (Baton) 686 

315.  Connections  of  Semi-circular  Canals  with  Central  Nervous  System.     (Paton).  687 

316.  I.  The  Mechanics  of  the  Auditory  Ossicles.      (After   Helmholtz.)     II.  Section 

of  the  Middle  Ear.     (Munk,  after  Hensen) 691 

317.  Schema  of  the  Semi-circular  Canals,  the  Posterior  Part  of  the  Skull  Removed. 

(Hedon,   after  Ewald)    695 

318.  Semi-circular  Canals  on  Right  Side  Destroyed      Commencing  rotation  of  head 

of  pigeon  about  five  days  after  operation.     (After  Ewald) 696 

319.  Twisting  of  the  Head  of  a  Pigeon  twenty  days  after  removal  of  all  the  semi- 

circular canals  on  the  right  side.     (Ewald,   J.   R.) 697 

320.  Position  of  Pigeon's  Head  after  removal  of  all  the  semi-circular  canals  on  both 

sides.     (Ewald,  J.   R.)    698 

321.  Diagram  of  Horizontal  Section  through  the  Human  Eye.     (Yeo) 700 

322.  Anterior-posterior   Section   of   the   Eyeball.      (Leveille) 701 

323.  Section  through  the  Human  Cornea.     (Bohm  and  Davidoff) 702 

324.  Corneal  Corpuscles  of  Dog.     (Bohm  and  Davidoff) 702 

325.  Corneal  Nerves  of  the  Pig.     (Rollet) 703 

326.  Diagram  of  the  Vessels  of  the  Eye.     (Leber) 704 

327.  Meridional  Section  of  the  Human  Ciliary  Body.     (Bohm  and  Davidoff) 705 

328.  Dissection    of   the   Zonula.      (After   Schultze) 706 

329.  Lateral  View  of  the  Orbit,  Showing  the  Nerves.     (Deaver) 707 

330.  The  Nervous  Mechanism  of  the  Iris 708 

331.  Isolated  Lens  Fibers.     (J.  Arnold) 709 

332.  Transverse  Section  of  Lens  Fibers.     (.1.   Arnold) 710 

333.  Anterior  Surface  of  the  Lens  of  an  Adult.     (J.  Arnold) 710 

334.  Diagram    of    the    Structure    of    Human    Retina   According    to    Golgi's    Method. 

(Greeff)    711 

335.  Hexagonal  Cells  from  the  Pigment  Layer  of  the  Retina  of  a  Rabbit.     (Ball)..  712 

336.  Action  of  the  Light  on  Retina.     Section  of  retina  of  frog.     (Englemann) 713 

337.  Right  Eye,   Normal   Fundus  Oculi.     (Ball) 714 

338.  Diagram  of  Occipital  Region  of  Right  Cerebral  Hemispheres.     (Ball) 715 

339.  Diagram  of  the  Lymph  Spaces  of  the  Eyeball.     (After  Fuchs) 717 


LIST  OF  ILLUSTRATIONS.  xv 

FIG.  PAGE 

340.  Schematic  Ej'o  Three  Times  Natural   Size.     (Landolt) 718 

341.  Diagram   Illustrating   Spherical   Aberrations.      (Ganot) 722 

342.  Scheme   of    Accommodation    for   Near   and    Distant    Objects.      (Landois,    after 

Helmholtz)    723 

343.  Refraction  of  Parallel  Rays  of  Light  in  Emmetropia  (E),  Hypermetropia  (//), 

and  Myopia  (Ji).     (Ball) 725 

344.  Different  Kinds  of  Lenses.     (Ganot) 726 

345.  Refraction  of  Rays  in  Regular  Astigmatism.     (Ball) 726 

346.  Diagram  Showing  Refraction  by  a  Double  Convex  Lens.     (Ganot) 727 

347.  Concave    Lens  Diverging  Parallel  Rays  of  Light.     (Lahousse^-   727 

348.  Purkinje-Sanson  Images.     (Ball)    728 

349.  Diagram  to  show  the  Blind  Spot  in  the  Visual  Field.     (Ball) 72S 

350.  Scheiner's  Experiment — an  experiment  to   determine  the  minimum  distance  of 

distinct  vision    729 

351.  Diagram  to  show  that  the  visual  angle  and  size  of  the  retinal  image  vary  with 

the  distance  of  the  object  from  the  eye.     (Ball) 729 

352.  Diagram   Showing   the   Corneal   Axis,    U-E;     the   Optic   Axis,    O-A;     the  Visual 

Line,  R-Y;    the  Line  of  Fixation,  R-J ;    and  the  Three  Angles.     (Ball)...  730 

353.  The  Horopteric  Circle  of  Muller.     (Ball) 731 

354.  The  Visual   Angle    732 

355.  Optogram  on  the  Rabbit's  Retina  of  a  Window  Four  Meters  Distant.     (Kuhne).  732 

356.  Diagram  Illustrating  the  Decomposition  of  White  Light  into  the  Seven  Colors 

of  the  Spectrum  in  Passing  Through  a  Prism.     (Beclard) 733 

357.  Wools  for  the  Detection  of  Color  Blindness.     (Oliver) 734 

358.  Diagram   Illustrating  Irradiation.      (Stirling) 736 

359.  Diagram  to  show  (1)  the  primary  position  of  the  right  eye;    (2)  the  eye  turned 

upward  and  inward,  and  (3)  downward  and  outward.     (Ball) 736 

360.  Muscles  Associated  in  Moving  the  Eyeballs  in  the  Directions  Indicated  by  the 

Arrows.      (Ball)    737 

361.  Positions  of  Images  in  Ocular  Paralyses.     (Ball) 738 

362.  Capsule  of  Tenon.     (Ball,   after  Merkel) 738 

363.  Diagram  Illustrating  Binocular  Vision.      (Beclard) 739 

364.  Lacrymal  and  Meibomian  Glands,  the  latter  viewed  from  the  posterior  surface 

of  the  eyelids.  The  conjunctiva  of  the  upper  lid  has  been  partially  dis- 
sected off,  and  is  raised  so  as  to  show  the  Meibomian  glands  beneath. 
(Raymond,  after  Testut)   740 

365.  Loring's  Ophthalmoscope    741 

366.  Direct  Ophthalmoscopy.     (Ball)    742 

367.  Indirect   Ophthalmoscopy.      (Ball)    742 

368.  The   McHardy   Perimeter.      (Brown) 743 

369.  Diagram  of  the  Normal  Visual  Field  for  White  and  Colors.     (Jennings) 744 

370.  Diagram  of  the  Visual  Tract.     (Ball) 745 

371.  Diagram  of  Right  Homonymous  Hemianopsia  and  of  the  sites  of  lesions  which 

may   cause  it.      (Ball)    746 

372.  Position  of  the  Nuclei  of  the  Cranial  Nerves.     (After  Edinger) 750 

373.  Distribution  of  the  Third  and  Sixth  Nerves  in  the  Orbit.     (Leveille) 752 

374.  Nuclei  of  Origin  of  the  Third  and  Fourth  Nerves.     (Poirier  and  Charpt) 754 

375     The  Origin  of  the  Trigeminal  Nerve   757 

376.  Ophthalmic  Division  of  the  Fifth  Nerve.     (Leveille) 758 

377.  Distribution  of  the   Sensory  Nerves  of  the  Head,   together  with  the   Situation 

of  the  Motor  Points  on  the  Neck.     (Landois) 760 

378.  Graafian  Follicle  from  Ovary  of  a  New-born  Child.     (After  P.  Strassman) 770 

379.  Human   Spermatozoon.     (Manton)    771 

380.  Transection     of    Chick    Embryo,     Showing    the    Three    Plastodermic    Layers. 

(Manton)     772 

381.  Diagram   Showing   Development  of   Spermatozoa  in   a   Seminal   Tubule.      (Mc- 

MURRICH)     773 

382.  Schema  to  Indicate  the  Process  of  Maturation  of  the  Spermatozoa.     (Boveri, 

Howell)     774 

383.  Diagram  Showing  Essential  Facts  in  the  Maturation  of  the  Egg.     (Wilson)...  774 

384.  Schema  to  Indicate  Process  of  Maturation  of  Ovum.     (Boveri,  Howell) 775 

385.  Schenjatic     Representation     of    the    Process    Occurring    During    Cell-division. 

(Boveri.  Howell)   776 

386.  Schematic   Representation    of   the   Process    Occurring   During   the   Fertilization 

and  Subsequent  Segmentation  of  the  Ovum.  The  cromatin  (chromosomes) 
of  the  ovum  is  represented  in  blue,  that  of  the  spermatozoon  in  red. 
(Boveri,    Howell)    778 

387.  Formation  of  Decidua   (the  decidua  is  colored  black,   the  ovum  is  represented 

engaged  between  two  projecting  folds  of  membrane).     (After  Dalton) 781 

388.  Projecting  Folds  of  Membrane  Growing  Around  the  Ovum.     (After  Dalton)...  781 

389.  Showing  Ovum  Completely  Surrounded  by  the  Decidua  Reflexa.      (After  D.\L- 

TON)    781 

390.  Diagram  of  an  Early  Stage  of  a  Primate  Embryo.     (Minot) 782 

391.  Uterus    at    Menstrual    Period,    Showing    Congested    Area    and    Destruction    of 

Mucous  Membrane.     (Photomicrograph  by  Gramm.)     (Gilliam) 786 

392.  Virginal   Uterus.      (Grandin  and  Jarman) 788 

393.  The  Foetal  Circulation.     (Grandin  and  Jarman) 789 


CHAPTER  I. 

THE  CELL. 

Observation  and  experience  tell  us  that  all  tangible  or  material 
things  about  us  are  either  dead  or  alive ;  that  is,  matter  is  either  life- 
less or  living. 

The  conception  of  life  in  its  simplicity  is  limited  to  a  few  ele- 
mentary phenomena,  such  as  nutrition,  evolution,  reproduction,  sen- 
sibility, and  motion.  These  properties  taken  together  distinguish  the 
living  from  every  form  of  lifeless  substance.  Combinations  of  these 
simple,  elementary  phenomena  give  us  every  complex  function  of 
our  present  life.  If  the  study  of  life  is  the  study  of  these  elemen- 
tary phenomena,  it  is  necessary  that  our  working  force  be  Ijrought 
to  their  seat  and  home — the  cell. 

Everywhere  there  is  a  sharp  line  or  division  between  living  and 
lifeless  matter,  although  the  two  are  frequently  so  closely  allied  that 
first  oljservations  seem  to  show  no  distinctions.  This  is  particularly 
true  of  those  things  that  are  not  seen  with  the  naked  eye — micro- 
scopical things.  When  one's  attention  is  brought  to  such  objects 
as  quartz,  iron,  the  earthworm,  or  the  dog.  the  distinction  is  very 
evident.  On  the  other  hand,  long  and  tireless  observation  and  inves- 
tigation are  required  to  determine  whether  some  of  the  bodies  found 
in  water  are  dead  or  alive.  And  although  so  closely  associated, 
scientists  have  found  that  a  living  substance  never  comes  of  its  own 
accord  from  a  lifeless  one,  but  only  through  the  influence  of  some 
other  living  matter.  For  example,  no  vegetation  springs  up  from  the 
soil  until  the  seed  (a  form  of  dormant  life)  becomes  buried  in  it;  no 
colony  appears  for  the  bacteriologist  on  the  sterilized  medium  until 
the  surface  is  impregnated  with  the  germ. 

Although  the  sharp  distinction  exists,  nevertheless  the  two  mate- 
rials are  very  closely  associated,  as  is  shown  by  a  little  observation. 
Plants  and  animals  are  kept  alive  and  nourished  by  the  food  they 
consume,  and  it  consists,  in  the  main,  of  lifeless  matter.  While  in 
the  body  it  seems  to  be  transformed,  as  it  were,  to  a  living  state,  and 
it  forms  part  of  the  body.  After  it  has  served  the  needs  of  the 
economy  of  the  plant  or  animal  it  dies,  and  is  gotten  rid  of  as  waste- 
matter. 

(1) 


2  PHYSIOLOGY. 

A  living  plant  or  animal  is  like  a  fountain  into  which  and  out 
of  which  material  is  constantly  ])assing,  but  the  fountain  maintains 
its  form  and  general  appearance.  Hu.xley's  simile  of  a  whirlpool  in 
a  stream  is  very  striking.  The  pool  remains  the  same  in  the  stream, 
but  water  enters  it,  becomes  a  part  of  it  as  it  is  whirled  around, 
then  passes  out  and  gives  place  for  other  to  enter.  The  pool  retains 
its  identity  all  the  while  that  its  elements  are  being  changed. 

The  contrast  between  living  and  lifeless  matter' forms  the  basis 
of  the  separation  of  the  natural  sciences  into  two  divisions :  the 
biological  and  physical  divisions,  biology  dealing  with  living  and 
physics  with  lifeless  matter. 

Biology  is  the  science  that  treats  of  living  things,  whether  ani- 
mal or  vegetable,  normal  or  abnormal.  It  deals  with  the  forms, 
structures,  and  origin,  together  with  the  functions  and  activities 
of  the  whole  animal  or  plant  or  its  various  parts.  In  fact,  its  scope 
is  so  wide  and  comprehensive  that  it  becomes  necessary  to  divide 
it  into  two  branches :    morphology  and  physiology. 

Morphology  is  that  part  of  the  science  that  deals  with  the  form 
and  structure  of  living  things,  together  with  their  arrangements. 

Physiology  is  the  science  that  treats  of  the  functions,  or  work, 
of  the  various  parts  of  the  living  organism,  and  what  each  one  does 
toward  the  economy  of  the  whole.  For  instance,  the  study  of  the 
form,  growth,  and  development  of  the  different  parts  of  the  brain, 
beginning  with  the  lamper-eel,  then  the  higher  fishes,  birds,  and 
mammals,  belongs  to  the  science  of  morphology.  By  comparisons  we 
see  that  in  the  lamper  there  is  merely  the  semblance  of  a  brain  in  its 
crudest  form,  showing  no  development  as  compared  with  the  brain  of 
the  higher  fishes  and  birds.  In  the  latter  we  notice  a  stronger 
development  in  one  department — the  optic  lobes.  The  cerebral  por- 
tion is  very  weak.  In  mammals  the  reverse  is  true,  and  it  reaches  its 
most  striking  size  in  man,  in  whom  the  cerebral  portions  are  extremely 
large  and  well  developed,  while  the  optic  lobes  are  relatively  small. 

The  study  of  the  functions,  for  instance,  of  the  heart  and  kid- 
neys belongs  to  the  science  of  physiology;  which  tells  how  the  heart 
by  its  alternate  contractions  and  relaxations  forces  the  blood  through 
the  circulatory  system  to  the  peripheral  parts  of  the  body  for  its  sus- 
tenance and  nutrition  and  to  the  lungs  for  its  purification  by  the 
elimination  of  the  carbonic  acid  and  the  absorption  of  the  oxygen ; 
and  how  the  kidneys  by  means  of  their  mass  of  tubes  and  cells  take 
from  the  blood  those  parts  that  are  no  longer  of  any  use,  fit  only 
to  be  expelled  from  the  body.     When  physiology  is  applied  to  man, 


THE  CELL.  3 

it  is  called  human  physiology,  for  the  great  and  ultimate  end  and  aim 
of  all  physiological  studies  is  the  understanding  of  the  functions  of 
ourselves.  Morphology  and  physiology  are  treated  as  though  they 
were  ahsolutely  distinct  sciences,  yet  they  are  so  closely  related  that 
the  division  is  made  only  for  convenience. 

Morphology  includes  in  its  category  such  subdivisions  as  anat- 
omy, histology,  and  embryology. 

Anatomy  is  the  science  that  treats  of  the  situation,  form,  and 
structure  of  the  various  parts  of  the  organism.  Anatomy  from  its 
root  keeps  in  mind  the  idea  of  cutting  or  dissecting,  and  as  com- 
monly used  at  the  present  time  deals  with  the  grosser  work  done 
upon  the  more  common  and  apparent  structures  of  the  body  with 
scalpel  and  forceps.  When  we  describe  in  all  their  detail  the  different 
organs  of  the  body  and  the  position  of  the  organs  to  one  another,  we 
call  it  descriptive  anatomy. 

Contrasted  with  anatomy  is  histology,  sometimes  called  micro- 
scopical anatomy.  Histology  is  the  science  that  deals  with  the  inti- 
mate structure  of  the  various  tissues  of  an  organism.  It  takes  up 
the  work  where  anatomy  ends;  as  it  brings  to  its  aid  the  microscope, 
it  can  delve  down  deeper  and  deeper  until  it  gives  us  knowledge  of 
the  component  parts  of  the  various  organs.  Histology  is  a  tissue- 
study.  Its  separation  from  anatomy  is  only  for  convenience,  and  is 
not  absolute. 

Embryology  is  the  science  of  the  development  of  the  adult  from 
the  ovum  or  germ.  It  gives  a  history  of  the  various  stages  of  develop- 
ment from  the  moment  of  impregnation  of  the  ovum,  until  the  adult 
is  reached.  Its  field  is  more  closely  associated  with  morphology 
than  physiology. 

Living  things  are  usually  found  in  separate  masses  and  these 
have  peculiarities  and  structures  of  their  own  which  give  to  them 
the  name  "organisms."  This  is  true  equally  of  the  large  masses, 
such  as  the  elephant  or  whale,  as  of  the  small  bodies  found  in  water 
or  the  bacteria  of  disease.  All  the  structures  of  the  latter  have  as 
yet  not  been  discovered  nor  dissected,  as  it  were,  since  the  microscope 
is  not  powerful  enough  and  our  supply  of  reagents  not  adequate 
enough  to  lay  bare  all  of  their  properties  and  forms. 

When  we  examine  some  of  the  contrivances  found  in  the  mechan- 
ical world,  such  as  a  watch  or  a  machine,  thoy  at  first  sight  appear 
to  us,  as  regards  their  identity,  single  individual  units;  that  is,  as 
one  watch  or  as  one  machine,  each  capable  of  doing  its  own  peculiar 
work.     Upon    closer    investigation,    we    perceive   that   each    is    com- 


4  PHYSIOLOGY. 

posed  of  a  variety  of  individual  parts,  each  of  which  has  its  own 
[jcculiar  share  of  the  work  to  be  done  and  bears  an  essential  relation 
to  tlie  working  of  the  whole.  In  the  watch,  the  springs,  pinions, 
levers,  and  niinierous  little  wheels  all  bear  certain  relations  to  one 
another  and  assist  in  the  running  of  the  watch. 

Similarly  we  find  that  it  is  characteristic  of  any  living  body  or 
organism — say,  a  dog  or  a  rose — that  it-  should  be  made  up  of  a 
number  of  diifercnt  and  distinct  parts  which  are  so  constructed  that 
they  may  assist  in  the  life  of  the  whole  organism.  The  animal  has  a 
head,  a  trunk,  limbs,  eyes,  ears,  etc.,  externally;  heart,  lungs,  liver, 
stomach,  intestines,  brain,  etc.,  internally.  To  these  parts  the  name 
organs  has  been  applied.  Thus,  the  organism  is  composed  of  distinct 
parts  called  organs.  The  division  of  the  body  into  organs  is 
purely  artificial. 

An  organ  is  a  particular  part  of  the  organism  that  has  a  certain 
specified  work  to  do.  For  example,  the  liver  is  a  certain  structure 
found  in  a  particular  situation  in  the  animal  and  has  assigned  as  its 
share  of  the  work  of  the  general  economy,  the  manufacture  of  the 
bile  to  aid  digestion.  So,  also,  the  eye  and  the  stomach  are  organs. 
They  are  particular  parts  of  the  organism  concerned  in  particular 
work;  the  eye,  in  sight,  or  vision;  the  stomach,  in  digestion. 

The  work  that  any  organ  does  is  called  its  function.  Since  the 
appearance  and  structure  of  the  various  organs  of  a  living  body  are  so 
varied,  therefore  we  do  not  expect  that  their  functions  are  any  more 
the  same  than  the  functions  of  the  watch  and  locomotive.  Thus,  the 
function  of  the  heart  is  to  pump  the  blood  to  all  parts  of  the  body; 
of  the  blood,  to  carry  nutritious  foods  to  all  parts,  and  at  the  same 
time  to  carry  away  certain  waste-products ;  of  the  kidneys,  to  excrete 
waste-matters  from  the  blood ;  of  the  brain,  to  have  a  general  over- 
sight and  to  govern  the  functions  of  the  whole  organism,  etc. 

Anatomy  is  the  forerunner  of  physiology  and  must  pave  the  way 
for  it.  For  how  are  we  to  study  the  functions  of  the  various  organs 
and  their  relations  to  one  another,  unless  we  are  acquainted  with  the 
structure,  form,  and  position  in  the  body  of  the  various  organs? 
Even  while  studying  physiology,  anatomy  must  run  hand  in  hand 
with  it,  particularly  that  modified  form  of  anatomy — histology,  or 
microscopical  anatomy — which  deals  with  the  minute  structures  and 
their  components — the  cells. 

We  have  learned  that  the  various  portions  of  the  living  body  are 
called  organs.  As  we  know,  each  organ  has  its  own  particular  work 
to  do.     By  careful  dissection,  we  find  that  an  organ — a  human  arm. 


THE  CELL.  5 

for  instance — is  made  up  of  a  variety  of  substances  called  tissues. 
There  are  bone-tissues,  cartilaginous  tissues,  muscle-tissues,  nerve- 
tissues,  etc..  all  different  in  structure,  yet  all  bundled  up  in  the  mem- 
ber called  the  arm  and  essential  to  it  to  perform  its  various  functions. 
The  brain  is  composed  of  two  distinct  tissues — the  gray  and  white 
tissues.  So,  in  like  manner,  any  of  the  organs  of  the  body  may  be 
resolved  into  various  parts  known  as  tissues. 

Thus  far  anatomy  has  aided  us  in  our  analysis  of  the  various 
parts  of  the  body,  for  it  has  to  deal  with  only  the  grosser,  coarser, 
and  more  obvious  forms  of  the  body.  So,  for  a  long  time,  physiology 
was  the  study  of  those  large  and  more  evident  organs.  Physiology 
could  not  go  further  until  it  had  more  exact  and  intimate  knowledge 
of  the  organs.  How  can  we  gain  correct  knowledge  of  the  working 
of  any  machine  unless  we  first  know  and  understand  the  construc- 
tion of  the  parts  of  the  machine? 

Chemistry  and  physics  teach  us  that  matter  is  made  up  of  simple 
forms,  called  elements  and  molecules,  respectively.  It  is  assumed 
that  the  units,  ultimately,  of  these  elements  and  molecules  are  definite, 
though  exceedingly  small,  material  particles.  These  particles  are 
called  atoms — the  word  meaning  that  the  particles  are  unable  to 
be  divided  without  losing  their  identity.  The  atom  of  the  chemist 
and  the  cell  of  the  physiologist  are  the  final  divisions  of  matter.  In 
the  physical  world  it  was  found  that  all  phenomena  were  due  to  the 
movements  of  these  small  particles — the  atoms. 

The  fact  that  animals  and  plants,  although  very  different  ex- 
ternally, are  made  up  of  the  same  anatomical  units  was  not  brought 
to  light  until  the  invention  of  the  microscope.  These  structural  units 
were  called  cells.  The  theory  that  organisms  were  made  up  of  cells 
was  suggested  by  the  study  of  plant-structure.  At  the  end  of  the 
seventeenth  century,  scientists,  by  means  of  their  low-power  micro- 
scopes, discovered  in  plants  small,  roomlike  spaces,  provided  with 
firm  walls  and  filled  with  a  fluid.  Because  of  their  similarity  to  the 
large  cells  of  the  honeycomb  these  small  structures  received  the  name 
of  cells.  To  the  scientists,  however,  the  principal  feature  seemed  to 
l^e  the  firm  walls.  By  study,  they  found  that  the  cell  absorbed  nutri- 
ent material,  assimilated  it.  and  produced  new  material.  Although 
plants  were  composed  of  a  mass  of  cells,  or  even  a  single  cell,  it  was 
found  that  each  cell  was  an  isolated  Avhole ;  that  it  nourished  itself 
and  built  itself  up.  The  cell-theory  was  also  applied  to  animal  tis- 
sues. By  its  use  it  was  found  that  many  of  the  tissues  were  formed 
also  of  cells  and  that  these  cells  appeared  to  be  of  similar  construction 


6  PHYSIOLOGY. 

to  those  in  plant  life.  Thus  we  find  that  every  tissue  is  composed  of 
minute  parts  known  as  cells  and  which  in  a  particular  tissue  are 
nearly  or  (|uite  similar.  For  instance,  in  examining  a  muscular  fiber, 
we  find  tliat  it  is  composed  of  very  small,  ribbonlike  units  called 
muscle-cells.  Although  differing  somewhat  in  size  and  development, 
yet  they  are  otherwise  similar ;  that  is,  muscular  tissue  is  composed  of 
muscular  units,  or  cells.  Cartilage  is  composed  of  oystershell-shaped 
cells;  mucous-membrane  cells  are  gobletlike,  and  secrete,  or  give  off, 
mucus.  Even  though  these  cells  are  self-supporting  and  grow  and 
form  other  cells,  in  the  higher  animals  they  are  grouped  and  held 
together  by  means  of  a  kind  of  cement,  spoken  of  as  "intercellular 
material.'' 

Hence  a  tissue  may  be  defined  as  a  group  of  similar  cells  having 
a  similar  function.     Tissues  are  different  only  because  they  are  com- 


Ip 

Fig.  1.— Vegetable  Cell.     (Duval.) 
up,  Cell-wall  of  cellulose,    n,  Nucleus,    ch,  Chlorophyll  bodies. 

posed  of  different  kinds  of  cells  having  functions  peculiar  to  them- 
selves. An  aggregation  of  cartilage-  and  muscle-  cells  gives  us, 
respectively,  cartilage-  and  muscle-  tissues. 

As  the  result  of  this  knowledge,  physiology  is  beginning  to 
develop  from  a  science  of  the  organ  and  its  functions  to  that  of  the 
cell  and  its  functions.  But  this  is  only  natural  as  a  form  of  develop- 
ment, since  we  first  consider  the  greater  and  more  active  functions 
of  the  organs  and  then  delve  down  deeper  and  deeper  until  we  reach 
the  functions  of  the  cell. 

Cells  are  characterized  by  the  presence  of  the  elementary  func- 
tions or  phenomena  of  nutrition,  growth,  reproduction,  etc.  If 
physiology  has  to  deal  with  them,  it  can  do  it  most  successfully  by 
studying  them  in  their  seat — the  cell. 


THE  CELL.  7 

The  vegetable  cell  is  known  from  the  animal  cell  by  the  presence 
of  cellulose. 

The  cell  of  the  vegetable  kingdom  in  its  respiration  takes  in 
oxygen  and  gives  off  carbonic  acid,  as  we  do,  but  in  its  nutrition  the 
action  of  the  suns  rays  u]X)n  the  chlorophyll  causes  it  to  break  up 
the  carbon,  to  fix  it  in  the  tissues,  and  to  give  off  oxygen.  This 
fixation  of  carbon  overshadows  in  daylight  the  ordinary  respiration  of 
the  plant,  which  goes  on  both  by  day  and  by  night.  Yeast-cells  break 
up  sugar  into  alcohol  and  carbonic  acid.  Besides  this  action,  they 
have  in  them  a  ferment,  invertin,  which  changes  cane-sugar  into 
invert-sugar,  which  is  a  mixture  of  dextrose  and  Isevulose. 

CELLS. 

We  have  learned  that  the  higher  forms  of  life,  whether  plants  or 
animals,  may  be  resolved  into  a  vast  number  of  very  small,  structural 
units,  called  cells.  The  skin,  muscles,  bone,  brain,  etc.,  appear  to 
the  naked  eye  to  be  composed  of  one  kind  of  substance  respectively. 
The  microscope,  however,  has  told  us  that  each  tissue  is  composed  of 
colonies  of  units,  held  together  by  intercellular  cement,  and  that  the 
units  or  cells  of  a  particular  tissue  are  similar  in  structure  and  func- 
tions. For  example,  upon  examination,  wo  find  that  muscular  tissue 
is  made  up  of  ril)bonlike  fibers,  similar  in  appearance  and  structure 
and  all  engaged  in  the  same  function — contraction.  Thus,  the  cell 
is  not  only  tlie  unit  of  structure,  but  also  of  function,  diseased  or 
normal. 

Animal  cells  are  of  various  sizes.  Although  differing  very  much 
in  shape  and  ajjpearance  in  various  parts  of  the  body,  nevertheless 
every  cell  consists  of  the  following  parts:  (1)  protoplasm.  (2)  mi- 
cleiis,  (3)  centrosomes,  and  (4)  various  matters  commonly  called 
"special  cell-const ituen ts." 

Max  Schultze's  definition  of  a  cell,  enlarged  by  later  research,  is : 
"A  mass  of  protoplasm  containing  a  nucleus." 

The  term  cell  as  employed  to-day  is  a  misnomer,  but  from  its 
constant  use  since  the  seventeenth  century,  it  has  gained  such  a  hold 
upon  the  minds  of  those  engaged  in  the  study  of  science  that  the 
attempt  to  supersede  it  with  a  more  appropriate  term  has  been  unsuc- 
cessful. However,  the  idea  that  it  originally  conveyed  has  been  some- 
what modified.  The  term  originated  among  the  botanists  of  the 
seventeenth  and  eighteenth  centuries,  and  was  applied  to  chamberlike 
elements,  separated  from  one  another  and  containing  a  fluid.  Their 
characteristic  and  most  important  feature  was  the  wall,  or  membrane. 


8  PHYSIOLOGY. 

in  which  were  supposed  to  lie  active  properties  of  the  coll.  Tlio 
liquid,  originally  called  plant-slimc,  was  named  protoplasm  by  von 
Mohl,  and  was  thought  to  be  a  waste-])roduct. 

That  the  wall,  or  inenibrane,  was  not  of  vital  importance  was 
clearly  dcmonsti'ated  by  later  researches.  The  study  of  the  ama'lja 
and  of  the  white  blood-corpuscle,  one-celled  organisms,  was  the  chief 
means.  These  organisms  are  capable  of  extending  their  Ijodies  into 
])rocesses — fine  threads  and  networks — as  they  move  about  from 
place  to  place,  taking  up  and  giving  off  matter  as  they  go.  They  pos- 
sess all  the  elementary  vital  functions,  and  yet  at  no  time  do  they 
possess  a  cell-membrane,  showing  that  the  protoplasm,  not  the  niem- 


Cell-inenibrane 


Reticulum  of  cell** 


Membrane  of  nucleus 


Nuclear    achromatic 
substance 


Nuclear  chromatic 
substance 


Fig.  2. — Cell  with  Reticulum  of  Protoplasm  Radially  Disposed.     From 
Intestinal  Epitlielium  of  a  Worm.      (Carxoy.  ) 

brane,  was  the  seat  of  the  functions.  An  immense  number  of  other 
unicellular  organisms  were  examined,  together  with  the  develop- 
ment of  other  plants  and  animals,  and  many  cells  devoid  of  a  mem- 
brane were  found. 


PROTOPLASM. 

The  protoplasm  of  unicellular  organisms  appears  as  a  viscid  sub- 
stance, which  is  almost  always  colorless  and  which  will  not  mix 
readily  with  water.  The  term  protoplasm  is  constantly  in  the  mouths 
of  the  physiologists,  and  it  is  difficult  to  give  it  a  rigid  definition, 
since  it  is  used  in  so  many  different  senses.  Hence,  we  commonly 
describe  protoplasm  as  a  living  substance  surrounding  a  nucleus, 
which  substance  may  or  may  not  be  limited  by  a  cell-wall. 


THE  CELL.  9 

Its  refractive  power  is  greater  than  that  of  water  and  in  it,  as 
a  medium,  very  delicate  threading  of  protoplasm  may  be  distin- 
guished. It  was  formerly  supposed  to  be  composed  of  a  homogeneous 
material,  and  destitute  of  any  structure  and  to  ccmtain  a  number  of 
minute  granules  of  a  solid  nature. 

Under  the  high  powers  of  the  microscope,  when  properly  stained 
with  reagents,  it  has  l)een  found  that  the  protoplasm  consists  of  two 
parts:  (1)  a  fine  network  of  fibers,  like  a  sponge,  called  the  reti- 
ciiJuni,  or  spoil gioplasm;  and  (2)  the  more  fluid  ])ortion  in  the 
meshes,  called  the  envlnjlcma,  or  liyaloplasm.     However,  it  must  be 


Fig.  3 


n,  Nucleus,     rr,  Contractile  vacuole.     A",  Food-vacuoles.    en,  Endoplasm. 
ck.  Ectoplasm. 

mentioned  that  the  views  concerning  the  structure  of  protoplasm  dif- 
fer, several  theories  being  .offered.  According  to  the  first  idea,  the 
protoplasm  forms  the  network,  the  nodal  points  of  which  appear  as 
individual  granules.  It  is  very  probable  that  many  of  the  larger  and 
more  obvious  granules  are  inert  bodies,  such  as  glycogen,  mucin, 
fat-g"lol)ules,  albuminous  substances,  etc.,  suspended  in  the  network. 
The  glycogen  granules  are  found  in  the  liver-cells,  the  fat-globules 
in  the  cells  of  the  lacteal  glands,  and  the  pigment-granules  in  the 
skin-cells  of  many  colored  animals.  Sometimes,  in  unicellular  ani- 
mals, calcareous  matters  are  found,  although  those  most  uniformly 
found  are  of  the  same  general  nature  as  the  protoplasm.  All  these 
particles,    or   granules,    are    termed    microsomes.     Besides,    tliere    are 


10  PHYSIOLOGY. 

occasionally  found  indigestible  bodies,  such  as  grains  of  sand,  indi- 
gestible residue  of  foodstuil's,  and  excretory  substances,  waiting  to 
be  expelled  from  the  body. 

Otiier  substances  found  within  the  pi'otoiiiasm  and  supposed  to 
be  of  great  importance  to  cell-life  are  drops  of  liquid — vacuoles,  as 
they  are  commonly  called. 

Specific   Gravity   of   Living   Protoplasm. 

Living  protoplasm  has  the  physical  property  of  having  a  greater 
specific  gravity  than  water.  When  cells  of  the  most  varied  kinds  are 
allowed  to  fall  into  water  they  sink  to  the  bottom.  In  some  cases  the 
protoplasm  contains  a  considerable  quantity  of  fat;  so  that,  although 
the  substratum  of  protoplasm  is  heavier  than  water,  the  floating  of 
the  cell  is  due  to  the  lighter  specific  gravity  of  the  fat-particles  over- 
coming the  heavier  specific  gravity  of  the  protoplasm. 

The  chemical  composition  of  protoplasm  (a  living  substance) 
can  be  obtained  only  after  it  has  been  killed.  However  paradoxical 
this  may  seem,  it  is  found  impossible  to  apply  the  methods  of  chem- 
istry without  killing  it.  Every  reagent  that  comes  in  contact  with  it 
disturbs  and  changes  it  and  eventually  kills  it.  Thus,  our  ideas  of 
the  chemical  composition  of  living  ])roto])lasms  are  the  ideas  we  get 
from  the  chemical  composition  of  dead  protoplasm. 

The  substances  of  which  it  is  comjDosed  are : — 

1.  Water. — Water  is  that  element  in  a  living  substance  that  gives 
it  its  liquid  nature,  allowing  its  particles  to  move  about  with  a  cer- 
tain degree  of  freedom.  In  the  cell,  water  occurs,  either  chemically 
combined  with  other  constituents  or  in  the  free  state.  Salts  occur 
dissolved  in  the  water.  Protoplasm  is  semifluid,  and  about  three- 
fourths  of  its  weight  is  due  to  water.  The  molecules  of  protoplasm 
are  thought  to  be  separated  from  one  another  by  layers  of  water. 

2.  Proteids. — The  proteids  take  a  very  active  and  essential  part 
in  the  functions  of  all  cells.  The  proteids  consist  of  the  elements 
carbon,  hydrogen,  sulphur,  nitrogen,  and  oxygen.  Proteids  occur 
both  in  the  protoplasm  and  in  the  nucleus,  but  with  this  difference: 
that  found  in  the  nucleus  has  combined  with  it  phosphoric  acid, 
forming  the  so-called  nucleins.  To  show  this  fact  is  very  easy,  for 
the  nuclein  of  cells  resists  the  action  of  digestion  hy  the  gastric  juice. 
All  kinds  of  cells  in  artificial  gastric  juice  have  their  protoplasm 
digested  and  only  the  nuclei  remain ;  that  is.  nuclein.  If,  now,  this 
nucleus  is  treated  with  stains,  it  shows  that  the  nuclear  bodies  consist 


THE  CELL.  11 

of  niiclein,  while  the  protopUism  of  the  cell  is  constructed  from  other 
albuminous  bodies. 

Protoplasm  is  composed  principally,  then,  of  simple  proteids  and 
compound  proteids  that  lack  phosphorus.  Our  most  common  and 
typical  type  of  an  albuminous  substance,  or  proteid,  is  the  white  of 
an  egg.  This  contains  12  per  cent,  of  actual  proteid  substance,  the 
remainder  being  chiefly  water.  The  albumins  are  the  only  bodies 
that  can  safely  be  said  to  be  found  in  all  cells.  Although  the  albu- 
mins contain  only  five  elements, — C,  H,  N,  S,  and  0, — yet  the  num- 
ber of  their  atoms  often  exceeds  a  thousand. 

3,  Various  Other  Substances  occur  in  smaller  proportions  as  car- 
bohydrates; as  glycogen  in  protoplasm  of  liver-cells;  fats,  seen  in 
protoplasm  as  fats  or  oil-drops ;  and  simpler  substances  which  are  the 
result  of  decomposition  of  the  proteids,  or  are  concerned  in  its  for- 
mation;  and  also,  inorganic  salts,  such  as  phosphates,  and  chlorides 
of  calcium,  sodium,  and  potassium. 

NUCLEUS. 

From  an  examination  of  the  protoplasm,  we  pass  on  to  the 
nucleus.  As  we  have  said  before,  "a  cell  is  a  mass  of  protoplasm  con- 
taining a  nucleus."  Various  properties  and  functions  of  an  import- 
ant nature  have  been  assigned  to  protoplasm,  but  it  is  found  that  the 
nucleus  is  equally  as  important.  The  classical  experiments  of  the 
old  observers  upon  protoplasm  led  them  to  believe  that  the  protoplasm 
was  the  embodiment  of  all  the  functions  of  life.  To  them  the  nucleus 
w^as  unessential  as  regards  the  activities  of  life.  The  ruling  power 
of  the  protoplasm  was  dismissed  when  it  was  found  that  the  nucleus 
in  reproduction  of  cells  by  division  or  impregnation  underwent  extra- 
ordinary changes,  while  the  protoplasm  remained  passive  and  quiet. 
Within  recent  years  there  has  set  in  a  reaction,  and  the  happy  mean 
'twixt  the  two  extremes  is  now  held  to  be  correct:  the  two  are  of 
equal  importance. 

By  extended  research  and  with  staining  reagents  such  as  carmin, 
hematoxylin,  etc.,  a  distinct  nucleus  was  found  imbedded  in  the  pro- 
toplasm of  most  animal  cells.  For  a  long  time,  and  until  the  micro- 
scope was  greatly  improved,  two  classes  of  organisms  appeared  to  be 
the  exceptions.  They  were,  monera,  the  lowest  and  sim])lost  organ- 
isms, and  bacteria.  Gradually  the  number  of  each  class  was  reduced 
until  at  the  present  day  it  may  safely  be  said  that  every  cell  contains 
a  distinct  nnclens.  Every  cell  may  thus  be  said  to  be  characterized 
by  two  general  cell-constituents,  protoplasm,  and  at  least  one  nucleus. 


12  PHYSIOLOGY. 

The  form  of  the  nucleus  is  different  in  various  cells.  Usually 
it  is  a  round  or  oval  body  situated  in  the  middle  of  the  cell.  Its 
rounded  ionu  is  considerably  expanded  in  young  cells,  as  in  tlie 
ovaries  in  their  evolution.  Very  fre(|U('nlly  the  form  of  the  element 
influences  that  of  the  nucleus.  Thus,  in  muscle-  and  nerve-  cells  the 
nucleus  is  generally  elongated.  In  the  lower  organisms  it  sometimes 
assumes  the  shape  of  a  horseshoe  or  a  twisted  strand,  or  is  very  much 
branched,  the  processes  running  out  in  every  direction  into  the  sur- 
rounding protoplasm. 

The  size  of  the  nucleus  is  usually  in  proportion  to  the  mass  of 
protoplasm  enveloping  it.  Thus,  in  the  large  ganglion-cells  of  the 
spinal  cord  the  nuclei  are  correspondingly  large.  Also  in  cells  en- 
gaged in  active  work,  the  nuclei  are  generally  of  good  size,  as  in  the 
secreting  cells  of  the  salivary  and  mucous  glands. 

As  to  the  number  of  nuclei  present  in  a  cell,  the  general  condition 
of  the  presence  of  but  one  in  a  cell  seems  to  prevail.  There  are  ex- 
ceptions, however,  as  liver-cells  very  frequently  contain  two,  and  the 
immense  cells  of  bone-marrow,  many. 

General  Substance,  or  Structure. 

The  nucleus  is  no  more  of  a  homogeneous  nature  than  the  proto- 
plasm and  presents  several  distinct  substances  and  structures.  The 
different  constituents  that  are  known  are  not  always  present  in  all 
cells,  at  all  times,  or  in  the  same  pro{)ortions.  Among  some  cells  one 
element  may  l)e  very  conspicuous,  while  in  some  otliers  it  is  scarcely 
to  be  found.  According  to  Verworn,  the  following  substances  occur 
most  constantly :  (1)  nuclear  sap,  (2)  acliromatic  nuclear  substance, 
(3)  chromatic  nuclear  substance,  and   (-1)  the  nucleolus. 

The  nuclear  sap  may  be  present  in  larger  or  smaller  quantities 
and  is  the  liquid  ground-substance  which  fills  up  the  interstices  left 
among  the  solid  nuclear  constituents.  In  many  cells  under  the  in- 
fluence of  certain  reagents,  and  even  in  life,  it  is  known  to  be  of  a 
very  fine  granular  nature. 

The  achromatic  nuclear  substance  is  a  structure  of  fine  threads 
found  in  the  nuclear  sap,  and  it  is  characterized,  as  is  also  the  latter, 
by  not  staining  with  the  usual  reagents;  carmin,  htematoxylin,  etc. 
It  contains  achromatin  or  linin. 

Lantanin  is  found  in  linin  in  the  form  of  fine  granules,  which 
stain  by  acid  anilin  dyes,  as  opposed  to  chromatin,  which  takes  up 
only  basic  anilin  dyes.  Hence  lantanin  is  called  oxychromatin, 
whilst  chromatin  is  known  as  basichromatin. 


THE  CELL.  13 

The  cliromatic  nuclear  substance,  as  its  name  implies,  has  an 
affinity  for  coloring-matter  in  the  form  of  different  stains.  It  is 
usually  in  the  form  of  a  continuous  network,  but  sometimes  appears 
in  small  granules,  or  particles.     It  contains  chromatin  or  nuclein. 

The  nucleolus,  if  it  appears  at  all,  is  found  in  the  network  of  the 
nucleus,  as  a  rounded  or  irregularly  shaped  body.  It  contains  para- 
nuclein  or  pyrenin  and  has  an  especial  affinity  for  color,  and  stains 
more  deeply  than  the  network.  The  nucleoli  are  thought  to  be 
passive  bodies  that  hold  in  reserve  different  constituents  which  are 
essential  to  the  life  of  the  nucleus. 

Sometimes  the  nucleus  is  enveloped  in  a  membrane,  called  the 
nuclear  membrane,  Avhicli  marks  it  distinctly  from  the  protoplasm. 
This,  however,  as  Avith  the  cell-membrane,  is  not  universal  and  is  not 
classed  as  a  general  constituent  of  the  nucleus.  The  sharpness  of  the 
contour  which  distinguishes  the  nucleus  in  the  midst  of  protoplasm 
led  many  histologists  firml}^  to  believe  that  the  nucleus  always  does 
possess  a  membrane.  The  truth  is  between  the  two  extreme  opinions. 
The  nucleus  can  very  readily  exist  without  one. 

The  nuclear  meml)rane  consists  of  an  achromatic  substance, 
amphipyrenin. 

A  portion  of  a  cell  deprived  of  its  nucleus  may  live  for  a  time, 
but  it  evinces  no  activities  or  functions  other  than  that  of  move- 
ment. It  neither  absorbs  food,  nor  grows,  nor  reproduces,  but  seems 
gradually  to  dwindle  away  and  die.  From  this  it  is  believed  that  the 
nucleus  exercises  some  powers  with  regard  to  the  building  up,  or  con- 
structive metamorphosis. 

Regarded  chemically,  the  nucleus  is  composed  principally  of  pro- 
teid  and  a  substance  like  proteid.  which  contains  as  much  as  10  per 
cent,  of  phosphorus.  Xo  doubt  there  are  others,  but  even  the  most 
delicate  chemical  reagents  kill  the  constituents  and  so  lessen  the 
opportunities  for  careful  investigation. 

CENTROSOME. 

About  twenty  years  ago,  when  nuclear  cell-division  was  being 
investigated,  a  small  body  other  than  the  nucleus  was  noticed  during 
the  division  of  the  cell  and  was  called  by  various  names :  polar 
corpuscle,  central  corpuscle,  or  centrosomc.  The  last  name  seems  to 
be  more  generally  used  at  the  present  time. 

The  centrosome  in  its  simplest  form  is  a  body  of  extreme  min- 
uteness, frequently  not  larger  than  a  microsome,  but  which  exerts  an 
active  influence  on  the  protoplasmic  structure  during  cell-division. 


14  PHYSIOLOGY. 

Because  of  its  influence  in  the  cell,  it  lias  aroused  more  interest 
among  investigators  than  any  other  conij)onent  of  the  celL  By  some 
it  is  considered  to  he  a  part  of  the  nucleus,  and  by  others,  of  the  pro- 
toplasm. As  a  rule,  it  lies  in  the  protoplasm  just  outside  of  the 
nucleus,  even  during  the  resting  stage,  and  in  certain  conditions  of 
tlie  cell  is  clearly  indicated  by  a  radiation  of  protoplasm,  attraction 
sphere,  or  archoplasm,  the  fibers  of  which  are  arranged  in  the  form  of 
a  star,  the  centrosome  heing  at  the  center. 

In  size  the  centrosome  ranges  between  that  of  the  ordinary  micro- 
some and  the  smallest  micro-organism.  No  structure  has  been  as  yet 
discovered  in  it.  It  cannot  be  classed  as  a  general  cell-constituent, 
since  many  forms  of  the  cell  and  unicellular  organisms  have  been 
examined  and  no  centrosome  found,  due  probably  to  the  inadequacy 
of  the  microscope.  Most  authors  consider  the  centrosome  as  an  essen- 
tial part  of  the  cell. 

The  centrosome  does  not  absorb  the  ordinary  stains  suitable  for 
the  nucleus,  but  requires  acid  anilin  dyes,  as  acid  fuchsin  and 
orange.     By  them  it  is  colored  vividly. 

As  a  rule,  there  is  one  centrosome  in  a  cell,  lying  close  to  the 
nucleus  and  surrounded  by  a  raylike  or  rodlike  structure  of  the  pro- 
toplasm. As  the  cell  prepares  for  division,  the  centrosome  divides 
into  two  distinct  parts,  both  lying  passively  within  the  starlike  net- 
work. When  tlie  daughter-cells  are  examined,  each  is  found  to  pos- 
sess one  of  the  centrosomes,  which,  as  the  cell  grows,  passes  through 
the  same  process  as  its  antecedents.  The  centrosome  is  regarded  as 
the  particular  organ  of  cell-division. 

PROTOPLASMIC    MOVEMENT. 

The  movements  of  protoplasm  are  movements  in  currents  and 
the  amoeboid  movement.  In  certain  vegetable  cells  protoplasm  moves 
and  causes  a  true  rotation  of  its  substance,  as  in  Chara ;  or  the  move- 
ment may  be  in  opposite  direction  and  the  paths  even  cross  over  each 
other.  In  this  movement  all  parts  of  the  protoplasm  do  not  move 
with  the  same  rapidity.  The  rate  in  protoplasm  is  about  V50  inch 
per  minute. 

Movements  differ  according  to  whether  the  protoplasm  is  nal-ed 
— without  any  enveloping  membrane — or  inclosed  ivithin  a  firm  wall, 
or  membrane. 


THE  CELL.  15 

I.  Movement   of   the   Naked   Protoplasm. 

Probably  our  most  common  and  typical  form  of  naked  proto- 
plasm is  presented  to  us  by  the  fresh-water  anwha,  found  in  stagnant 
water.  The  anireba  is  a  unicellular  organism,  about  Viooo  i^^^'^^  i^^ 
diameter,  possessing  one  or  more  nuclei,  and  is  almost  continually  in 
motion,  due  to  its  extending  numerous  protoplasmic  projections, 
called  pseudopodia  (false  feet).  It  then  rolls  its  entire  mass  into 
the  pseudopodium,  or  fingerlike  projection,  only  to  continue  the  same 
operation  repeatedly  during  its  life. 

The  pseudopodia  assume  different  forms  and  shapes  in  the  differ- 
ent kinds  of  cells,  and  in  this  way  the  establishment  of  the  identity 
of  a  cell  is  frequently  aided  by  an  observation  of  the  processes.  For 
example,  most  of  the  fresh-water  amoeba  possess  broad,  lobate  or 
finger-shaped  pseudopodia;  leucocytes,  white  blood-corpuscles, 
divided  and  pointed  pseudopodia;  some  of  the  rhizopods  and  pigment- 
cells,  threadlike  and  reticular  pseudopodia  which  flow  into  one 
another. 

In  the  human  body  some  of  the  cells — such  as  white  blood- 
corpuscles,  lymph-corpuscles,  and  connective-tissue  cells — possess 
movements,  which,  because  of  their  likeness  to  those  of  the  amoeba, 
are  called  amcehoid. 

1.   Ciliary   Movement. 

There  have  been  discovered  cells  and  unicellular  organisms 
possessing  delicate,  hairlike  processes,  which  extend  in  greater  or  less 
numbers  from  their  surfaces.  They  are  called  flagella,  or  cilia. 
These  resemble  very  thin  pseudopodia  when  they  are  composed  of 
hyaloplasm  alone,  as  the  cilia  and  flagella  are  homogeneous  and 
nongranular  in  nature.  However,  they  differ  from  pseudopodia  in 
that  their  movements  are  very  energetic  and  always  definite,  and 
also  that,  unlike  pseudopodia,  their  structures  are  not  temporary, 
but  permanent,  being  neither  protruded  nor  withdrawn.  The  ciliary 
cells  lining  the  trachea  are  subjects  for  examination.  The  deep 
back  part  of  the  throat  of  a  frog  is  gently  scraped  and  the  scrapings 
placed  in  a  dro]i  of  water  upon  a  warm  stage.  When  we  examine 
the  cells  under  the  microscope,  we  see  upon  their  surface  a  constant 
rapid  movement ;  l)ut  the  movement  is  so  rapid  that  we  see  onlv  the 
motion,  and  not  tlie  vibrating  cilia.  If,  however,  the  vibrations  be 
lowered  to  about  a  dozen  per  second,  we  are  then  able  to  see  the 
cilia   themselves.     Ciliary   movements   are   of   various   kinds.     More 


16  PHYSIOLOGY. 

frequently  it  is  a  movement  of  elevation  and  deju'ession  of  tlic  cilia; 
sometimes  it  is  like  the  extension  and  flexion  of  our  fingers,  at  other 
times  a  sort  of  wave  or  whirlpool-like  movement.  In  these  move- 
ments all  the  cilia  on  the  surface  move  in  the  same  direction,  like  a 
field  of  grain  before  tlie  wind.  Each  completed  movement  of  the 
cilia  is  composed  of  two  movements  of  unequal  duration,  the  longer 
corresponding  to  contraction,  and  the  shorter  to  relaxation  of  the 
cilia.  Ciliary  movements  may  be  of  a  high  rapidity,  as  many  as 
960  to  about  1000  per  minute,  and  entirely  independent  of  the  circu- 
lation and  the  nervous  system.  These  movements  are  able  to  con- 
tinue after  death  as  long  as  a  day,  while  in  frogs  they  have  been 
observed  for  many  days. 

Cilia  are  about  '^/sooo  i'lch  in  length  and  are  able  to  perform 
some  work.  By  their  movements  they  are  able  to  float  a  cell  in  a 
liquid,  such  as  water,  even  though  the  cell  and  cilia  are  composed,  in 
a  great  part,  of  protoplasm,  whose  specific  gravity  is  heavier  than 
water  and  naturally  inclined  to  sink,  and  at  the  same  time  they  pro- 
pel the  cell  in  some  definite  direction  at  a  much  faster  speed  than  that 
obtained  by  the  protrusion  and  retraction  of  pseudopodia.  The 
function  of  the  ciliated  cells  does  not  appear  to  be  of  any  particular 
importance  in  man  except  that  in  the  trachea  their  movements  bring 
to  the  larynx  foreign  substances  that  have  been  inhaled  into  the  lungs, 
such  as  dust,  etc.,  and  to  bring  up  for  expectoration  the  thickened 
mucus  that  is  formed  during  the  stages  of  a  cold. 

A  practical  illustration  of  the  effects  of  the  protoplasmic  move- 
ments of  leucocytes  (white  blood-corpuscles)  can  be  observed  when  an 
injury  occurs  to  any  part  of  the  body.  As  a  result  of  the  injury  and 
as  an  attempt  at  repair,  more  blood  is  sent  to  the  injured  part.  This 
result,  called  congestion,  gives  to  it  its  red  color.  With  the  additional 
quantity  of  blood  comes  an  additional  numl)er  of  leucocytes.  They, 
by  protoplasmic  movements,  pass  through  the  walls  of  the  capillaries 
to  the  seat  of  the  injury,  to  take  up  dead  portions.  Sometimes  bac- 
teria lodge  in  the  wound,  which  the  leucocytes  approach  and  kill  by 
ingestion,  as  it  were,  thus  rendering  them  harmless.  This  process  of 
ingesting  bacteria  and  other  foreign  substances  is  called  phagocytosis, 
and  hence  the  leucocytes  are  sometimes  termed  phagocytes. 

The  phenomenon  of  a  leucocyte  in  active  movement,  which  by 
one-sided  action  of  the  chemical  products  of  bacteria,  as  toxins,  moves 
toward  (positive)  or  away  (negative)  from  the  bacteria,  is  called 
chemotaxis. 


THE  CELL.  17 

CELL=DIVISION. 

We  have  learned  that  organs  are  composed  of  various  structures, 
called  tissues.  A  tissue  may  be  defined  as  "a  group  of  similar  cells 
having  similar  functions."  For  example,  muscular  tissue  is  made  up 
of  ribbonlike  muscle-cells;  mucous  tissue  of  secreting,  goblet-shaped 
cells;  nervous  tissue  of  ganglion-cells,  with  their  numerous  project- 
ing dendrons,  etc. 

By  observation  we  notice  a  variety  of  tissues  due  to  a  variety  of 
kinds  of  cells;  also  that  all  tissues  of  a  kind  are  not  necessarily  of 
the  same  bulk,  size,  or  weight. 

The  chick  contains,  in  its  body,  a  number  of  organs  of  a  definite 
size  and  consistency.  It  has  a  head,  limbs,  muscles,  a  heart,  lungs, 
intestines,  a  liver,  etc.  We  see,  of  course,  that  these  organs  are  of  a 
size  and  weight  in  proportion  to  their  age— none  of  them  large  or 
heavy.  Upon  examination,  we  find  the  tissues  of  the  various  organs 
to  be  composed  of  cells  such  as  we  should  expect  them  to  contain; 
that  is,  the  muscles  of  muscle-cells,  'the  bones  of  osseous  cells,  the 
brain  of  ganglion-cells,  etc.  Furthermore,  although  cells  are  of  dif- 
ferent sizes  and  forms,  yet  there  is  very  little  difference  in  respect 
to  size  between  the  cells  of  a  particular  tissue,  as  compared  with  one 
another,  or  with  those  of  the  adult  animal;  for  the  size  of  every  cell 
is  definite. 

When  we  observe  the  same  animal  one  year  after  its  birth,  we 
notice  some  striking  differences :  it  is  much  larger  and  heavier,  the 
various  organs  are  fuller,  more  compact,  and  show  the  effects  of  the 
development  as  it  approached  maturity.  The  head,  brain,  muscles, 
heart,  lungs,  intestines,  etc.,  are  all  much  larger  and  better  developed 
than  those  found  in  the  small  chick.  However,  if  a  microscopical 
examination  be  made  of  the  various  tissues  in  this,  the  adult  animal, 
what  do  we  find  and  how  do  the  cells  compare  with  those  of  the  chick  ? 
Nothing  remarkable  in  the  individual  cells  themselves.  The  liver- 
cells  of  the  adult  are  no  larger  than  those  of  the  chick,  nor  are 
the  ganglion-,  muscle-,  or  other  cells.  What  we  do  perceive  is  a 
great  increase  in  the  mimler  of  the  cells  in  any  particular  tissue. 
The  liver  and  brain  of  the  adult  animal  contain  many  more  cells  than 
the  same  organs  of  the  chick.  Thus  we  see  that  there  has  been  a 
growth  due,  not  to  larger  cells,  but  to  a  greater  number  of  cells. 
That  is.  the  cells  have  multiplied. 

Similarly,  as  the  infant  passes  through  the  various  stages  of  boy- 
hood, youth,   and  manhood,  we  say  that  he  grows,  for  there  is  an 

2 


18  PHYSIOLOGY. 

increase  in  the  size  and  weight  of  the  various  organs  of  his  body. 
This  means  that  there  is  a  greater  number  of  cells  composing  tlie 
tissues  of  his  various  organs.  The  power  to  multiply — that  is,  pro- 
ducing new  forms  similar  to  itself — is  one  of  the  most  important 
and  characteristic  functions  of  the  cell.  By  this  attribute,  it  not 
only  is  able  to  maintain  its  own  particular  kind,  or  species,  but  can 
undergo  constructive  metamorphosis:  building  up,  or  growing,  until 
any  part,  or  organ,  is  matured. 

A  cell  multiplies  by  dividing  into  two  or  more  parts.  Each 
part  is,  of  course,  smaller  than  the  original  or  mother-cell,  but,  by 
assimilating  nutrient  material  from  the  surrounding  tissues,  it 
grows  until  each  part  is  the  size  of  the  mother-cell,  when  it  also  is 
ready  for  division,  or  reproduction. 

No  cell  exists  that  has  not  had  its  origin  in  some  pre-existing 
cell.  In  animals  whose  tissues  are  composed  of  many  cells,  these 
same  tissues  can  be  traced  back  to  single  cells,  of  which  they  are 
developments.  The  animal  itself,  with  all  its  many  and  various 
parts  and  structures,  originated  •  from  a  single  cell,  the  germ-cell,  or 
ovum,  which  have  existed  in  the  parent-body,  is  also  derived  from 
a  cell. 

Schleiden,  the  botanist  and  accredited  discoverer  of  the  cell- 
theory  among  plants,  and  Schwann,  to  whom  Schleiden  confided  his 
views  and  ideas  of  plant-structure,  and  who  then  reduced  animal  tis- 
sues to  their  structural  units,  the  cells,  were  anxious  to  know  the 
origin  of  the  cells.  To  them  the  presence  of  the  nucleus  was  known, 
and  even  the  nucleolus;  but  their  instruments  were  not  powerful 
enough  to  allow  of  their  penetrating  deeper,  and  of  getting  the  cor- 
rect ideas  of  cell-division. 

It  was  proved  in  1858  that  cells  multiplied  as  a  result  of  the  divi- 
sion of  the  two  equally  essential  parts  of  the  cell,  the  nucleus  and 
protoplasm.  Our  present  conception,  that  the  two  are  of  equal  im- 
portance and  value,  dates  from  this  time.  It  was  asserted  that  the 
division  began  within  and  proceeded  to  the  outer  parts  of  the  cell. 
That  is,  the  nucleolus  was  divided,  its  division  was  followed  by  sepa- 
ration of  the  nucleus,  and  this,  in  turn,  followed  by  constriction  and 
division  of  the  protoplasm  with  its  enveloping  membrane.  These 
views  were  confirmed  liy  Virchow,  who  formulated  the  doctrine 
"Omnis  cellula  e  cellula"   (every  cell  from  a  cell). 

Later,  it  was  discovered,  by  the  investigation  of  some  of  the 
tissue-cells,  that  the  process  of  division  was  not  so  simple  as  expected. 
In  some  cases,  it  was  found  that  the  nucleus  became  star-shaped,  or 


THE  CELL.  19 

lobed,  or  even  seemed  to  disappear  altogether  before  cell-division.  A 
few  years  later,  it  was  seen  that  the  process  of  division  was  compli- 
cated in  the  extreme,  and  that  the  cell-nucleus  underwent  a  variety  of 
transformations,  assuming  different  shapes  and  figures  until  two 
daughter-cells  were  formed  from  the  mother-cell.  This  process  was 
afterward  named  kanjokinesis. 

By  experiment,  it  was  demonstrated  that,  if  a  cell  in  a  living 
organism  or  tissue  was  so  divided  that  one  of  the  parts  was  composed 
of  protoplasm  only,  none  of  the  nucleus  being  present,  the  proto- 
plasmic part  continued  to  live  for  a  considerable  time,  but  that,  of 
the  vital  phenomena  exhibited  by  the  normal  cell,  it  possessed  only 
that  of  movement.  It  was  unable  to  take  up  from  the  surrounding 
tissues  a  proper  amount  of  nutrition,  so  that  growth  and  reproduc- 
tion never  occurred,  and  after  a  time  it  died.  Thus  it  was  concerned 
only  in  destructive,  not  constructive,  metamorphosis.  It  was  totally 
unable  to  build  itself  up,  to  grow,  or  reproduce  others  of  its  species. 
On  the  other  hand,  the  part  containing  the  nucleus  grew  and  repro- 
duced its  kind,  forming  daughter-cells,  that  in  turn  formed  other 
cells,  etc. 

Thus,  in  order  that  the  daughter-cell  may  possess  the  same 
properties,  form,  and  functions  of  the  mother-cell, — in  a  word,  in 
order  that  it  may  live, — it  becomes  necessary,  in  the  division,  that 
both  the  nucleus  and  the  protoplasm  must  divide.  The  disposition 
of  any  cell  to  divide,  or  reproduce,  is  usually  announced  by  changes 
in  its  nucleus,  both  physical  and  chemical.  In  fact,  the  division  of 
any  cell  is  preceded  by  division  of  the  nucleus.  This  process  in  the 
cells  of  most  organisms  is  very  complicated,  whereas  the  division  of 
the  protoplasm  is  most  simple,  consisting  of  the  appearance  of  a  con- 
striction, which  becomes  deeper  and  deeper,  forming  a  groove,  or 
fissure,  until  eventually  the  mass  is  divided  into  two  parts. 

The  evident  importance  of  the  relation  of  the  nucleus  to  cell- 
division  has  led  to  extended  study  of  the  nucleus  and  its  transforma- 
tions during  the  process  of  reproduction,  with  the  result  that,  upon 
its  function  in  this  respect,  three  forms  of  division  are  recognized: 
(1)  direct  cell-division.  (2)  indirect  cell -division,  and  (3)  endogenous 
nuclear  multiplication. 

I.  Direct   CelNdivision    (Amitosis). 

Direct  cell-division  is  very  rare,  and  present  only  in  some  of  the 
unicellular  organisms  and  leucocytes.  In  pathological  formations, 
however,  such  as  tumors,  this  form  of  division  occurs  very  frequently. 


20  PHYSIOLOGY. 

To  get  a  better  conception  of  the  direct  form  of  division,  we  will 
study  one  of  the  infusorians,  the  typical  amoeba,  and  the  changes 
occurring  in  it  during  reproduction.  The  first  intimation  of  a  divi- 
sion is  noted  in  the  spherical  nucleus,  which  becomes  elongated,  the 
middle  portion  of  it  being  indented  by  a  constriction,  which  gives  to 
the  nucleus  a  dumb-bell  shape.  The  constricted  portion  becomes 
gradually  narrower  and  slenderer  until  the  two  heads  of  the  ball  sepa- 
rate and  each  assumes  the  same  shape  as  its  mother — spherical.  The 
cell  thus  contains  two  distinct  nuclei.  Following  the  division  of  the 
nucleus  is  that  of  the  protoplasm  by  constriction  also.  The  indenta- 
tion always  appears  between  the  two  nuclei.  Eventually  two  cells 
are  thus  formed,  each  with  a  separate  nucleus;  each  daughter-cell  is, 
of  course,  smaller  than  its  mother,  but  by  the  assimilation  of  the 
nutrient  material  surrounding  it.  it  soon  grows  to  the  normal,  definite 
size.  Tliis  process  often  requires  several  hours  for  its  completion, 
the  various  stages  being  frequently  accomplished  in  an  uncertain 
manner. 

2.   Indirect  Cell=division   (Mitosis,  or  Karyokinesis). 

By  far  the  greater  number  of  animal-  and  plant-  cells  follow  the 
more  complicated  and  intricate  method  of  indirect,  or  Tcary akinetic, 
form  of  division.  The  division  of  the  protoplasm  is  simple  enough, 
following  only  the  laws  of  constriction  until  the  mass  is  completely 
separated  into  two  parts,  by  means  of  a  furrow,  or  fissure.  It  is  the 
nucleus  which  undergoes  very  remarkable  and  typical  changes,  very 
complicated  in  their  nature,  but  which  in  plants  and  animals  are  con- 
stant and  agree  very  much  in  regard  to  essentials.  Thus  the  indirect 
method  is  very  nearly,  though  not  quite,  universal. 

As  a  cell  prepares  for  division  the  most  evident  and  important 
fact  noticed  is  a  change  in  its  nucleus,  both  physical  and  chemical. 
The  nucleus  becomes  somewhat  enlarged,  and  its  chromatic  nuclear 
substance,  or  chromoplasm, — so  called  because  it  has  an  affinity  for 
stains, — ^begins  to  become  changed  little  by  little,  from  the  netlike 
arrangements  of  its  minute  granules  and  particles,  until  the  substance 
is  arranged  in  the  form  of  threads  loosely  rolled  up,  like  a  coil  or 
convolution,  called  the  sl-ein  or  spirem.  These  consist  principally 
of  nuclein,  and  stain  more  deeply  than  the  surrounding  parts,  and 
are,  hence,  more  easily  discerned.  It  is  the  presence  of  these  threads 
that  gives  to  the  process  the  name  mitosis.  In  most  cases  there  is 
but  a  single  thread,  which  is  coiled  or  convoluted  throughout  its 
entire  length ;  occasionallv.   there   occur   several   such  threads.     The 


THE  CELL.  21 

threads  are  somewhat  thicker  than  before,  and  more  separated  than 
during  the  resting  stage.  With  the  formation  of  the  spirem,  or 
wreath,  the  nucleoli  and  membrane,  if  any,  disappear.  In  some  cases 
the  nucleoli  are  dissolved  and  cast  into  the  hyaloplasm,  where  they 
degenerate  and  have  no  further  function. 

The  thread  of  the  spirem  becomes  divided  transversely  into 
nearly  equal  parts,  or  bodies,  known  as  chromosomes,  which,  in  most 
cases,  are  in  the  form  of  rods,  straight  or  curved.  The  ground- 
substance  of  the  nucleus  now  becomes  a  part  of  the  surrounding  hyalo- 
plasm. The  chromosomes  at  first  are  placed  rather  irregularly,  but 
they  soon  begin  to  arrange  themselves  into  a  more  definite  form,  that 
of  a  rosette.  The  curved  chromosomes  now  become  more  angular 
and  V-shaped,  the  angle  pointing  toward  the  center  of  the  nuclear 
space  while  the  free  ends  are  directed  toward  the  circumference,  this 
figure  being  called  the  aster,  or  garland.  While  in  the  form  of  the 
aster  each  chromosome  splits  longitudinally  into  halves,  so  that  we 
have  just  again  as  many,  though  thinner,  chromosomes. 

Before  the  membrane  has  been  dissolved,  there  appear  in  the 
protoplasm,  but  very  near  the  nuclear  membrane,,  two  small  granules 
lying  side  by  side.  These  are  the  centrosomes.  They  are  of  a  sub- 
stance that  stains  with  difficulty.  Gradually  they  begin  to  separate 
from  one  another,  moving  in  a  semicircle,  until  they  are  diametrically 
opposite  one  another,  or  at  the  nuclear  poles.  While  they  have  been 
in  motion,  the  nuclear  membrane  has  been  dissolving,  so  that,  by  the 
time  they  are  again  at  rest,  the  membrane  has  disappeared.  The 
achromatic  nuclear  spindle  develops  between  the  centrosomes.  When 
they  begin  to  separate,  the  spindle  is  small,  scarcely  discernible,  and 
like  a  band  in  form.  As  the  centrosomes  separate  more  widely,  the 
fibers  become  more  plainly  visible  and  assume  the  form  of  a  spindle — 
broad  in  the  middle  and  converging  at  either  end,  toward  and  end- 
ing in  the  centrosomes.  The  protoplasm  now  arranges  itself  around 
the  centrosomes  in  the  form  of  ravs  of  a  star,  as  though  the  filaments 
of  protoplasm  were  attracted  by  the  centrosomes  in  the  manner  of 
iron  filings  by  a  magnet.  At  first  these  fibers  are  small,  but  increase 
in  length  and  numbers  as  the  division  of  the  cell  progresses,  until  they 
run  throughout  the  entire  protoplasmic  mass. 

The  V-shaped  filaments,  called  chromosomes,  are  now  collected 
in  the  plane  of  the  equator,  called  the  equatorial  plate.  While  the 
chromosomes  have  been  arranging  themselves  in  the  plane  of  this 
plate,  they  have  been  growing  somewhat  shorter  and  thicker,  their 
angles  pointing  to  the  axis  of  the  spindle  and  their  ends  to  the  cir- 


22  PHYSIOLOGY. 

eiimference.  By  the  contraction  of  the  spindle  fibers  the  daughter- 
chi'oinosomes  (the  result  of  the  original  chromosomes  being  divided 
Jongitiidinally  into  two  separate  halves  by  means  of  fission)  are 
divided  into  two  equal  groups,  which  are  moved  toward  the  points, 
or  poles,  of  the  spindle,  but  never  reach  it  absolutely.  Between 
these  groups  fine  "connecting  fibrils"  stretch.  This  figure  is  called 
the  double  star,  or  diaster.  The  star  shape  is  formed  by  the  angles 
of  the  chromosomes  being  arranged  next  to  the  centrosomes,  with 
their  free  ends  extending  out  radially. 

There  now  follows  a  retransforming  of  the  daughter-chromo- 
somes, arranged  in  the  form  of  a  star,  into  a  genuine  resting  nucleus. 
The  angles  begin  to  disappear,  the  threads  draw  more  closely  to  one 
another,  becoming  more  bent  and  roughened  at  the  same  time  that 
little  processes  appear  on  their  surfaces.  A  very  delicate  nuclear 
membrane  develops  and  surrounds  the  group  of  threads.  The  radi- 
ating fibers  of  protoplasm  around  the  centrosomes  become  more  and 
more  indistinct  until  they  finally  disappear.  The  same  thing  occurs 
with  the  "connecting  fibrils." 

When  the  two  daughter-stars  are  separated  as  far  as  possible 
there  appears  on  the  surface  of  the  cell-body  a  fissure,  cutting  into 
the  protoplasm  in  the  line  of  the  equatorial  plate,  imtil  the  cell  is 
completely  divided  into  two  parts,  each  containing  a  nucleus. 

The  duration  of  this  process  has  been  seen  in  man  to  he  half  an 
liour,  while  in  the  larvce  of  the  salamander  it  has  been  known  to  take 
as  long  as  five  hours. 

The  whole  process  of  mitosis  may  be  divided  into  five  stages: — 

1.  Prophase   (skein  stage). 

2.  Mother-star  stage    (monaster). 

3.  Metaphase-Metakinesis  (diaster). 

4.  Anaphase  (daughter  skeins). 

5.  Telophase   (daughter  nuclei). 

3.  Endogenous   Nuclear   Multiplication. 

A  third  rare  mode  of  nuclear  multiplication,  to  which  is  given 
the  above-named  title,  was  discovered  in  the  thalassicola. 

The  thalassicola,  which  is  the  largest  in  size  of  the  radiolarians 
and  the  diameter  of  whose  central  capsule  is  nearly  equal  to  that  of 
the  frog's  egg,  has,  during  the  major  portion  of  its  life,  one  single, 
highly  differentiated,  giant  nucleus,  called  the  internal  vesicle.  This 
nucleus,  or  internal  vesicle,  usually  attains  to  V,^  inch  in  diameter, 


THE  CELL. 


23 


and  possesses  a  thick,  porous,  nuclear  meniljrane.  It  is  very  similar 
to  the  multinucleated  germinal  vesicle  of  the  ovum  of  an  amphibian. 
Simultaneously  with  the  advent  of  the  centrosome  into  the  proto- 
plasm, there  appeared  in  the  latter,  which  heretofore  has  been  entirely 
free  and  clear,  a  large  number  of  very  small  nuclei.  These  act  as 
centers,  around  each  one  of  which  there  develop  nucleated  zoospores, 
which  may  amount  finally  to  as  many  as  some  hundreds  of  thousands 
of  separate  cells. 


JV---- 


Fig.  4. — To  Show  the  Changes  in  the  Nerve-cell  Due  to  Age. 
(From  Howell.) 

A,  Spinal  ganglion  cell  of  a  still-born  child.  B,  Spinal  ganglion  cell  of  a 
man  dying  at  92  years  of  age.  N,  Nuclei.  In  the  old  man  the  cells  are  not 
large,  cytoplasm  is  pigmented,  the  nucleus  is  small  and  the  nucleolus  much 
shrunken  or  absent.  Both  sections  taken  from  the  cervical  ganglion.  250 
diameters.     (Hodge.) 

Fatigue  of  Cells. — Hodge,  of  Clark  University,  has  found 
changes  in  the  cell  corresponding  to  rest  or  activity.  Thus  the  nerve- 
cell  in  the  morning  has  a  clear,  round  nucleus,  while  in  the  evening, 
being  tired  from  work,  the  nucleus  has  an  irrccrular  contour. 


LlTER.\TURE  COXSULTED. 

Verworn,  "General  Physiologj^"  1899, 
Hertwig,  "The  Cell,"  1895. 


CHAPTER  II. 

(a)  CHEMICAL  CONSTITUENTS  OF  BODY  AND  FOOD, 
(b)  ALIMENTARY  SUBSTANCES. 

Digestion  has  been  described  as  the  physical  and  chemical  alter- 
ation of  the  foodstuffs  into  forms  better  lifted  for  absorption  by  the 
action  of  certain  soluble  ferments,  the  digestive  enzymes. 

The  animal  organism  had  its  birth  in  a  single  ovum  or  cell,  which, 
under  certain  favoring  circumstances  and  conditions,  developed  into 
a  mass  of  simple  cells.  As  development  proceeded,  this  aggregation 
became  differentiated  into  tissues,  l)y  the  grouping  of  tlie  cells,  altered 
by  chemical  changes  in  the  substance  of  the  cells  themselves,  by 
alterations  in  their  shapes,  and  by  deposits  of  intercellular  substances. 
As  the  organism  continued  to  grow,  the  various  parts  became  more 
and  more  complex  by  use  and  development  until  it  presented  a 
highly  complex  unit. 

In  the  metabolism  of  the  cell  it  was  learned  that  the  various  cells 
while  performing  their  various  vital  phenomena  must  constantly 
maintain  a  very  nice  balance  in  respect  to  waste  and  repair.  That  is, 
the  various  kinds  of  cells  took  out  from  their  environuients  those  sub- 
stances that  were  necessary  for  their  economy  to  build  themselves  up 
and  grow,  while  the  waste-products  were  excreted.  A  distinctive 
property  of  the  cells  was  the  selective  power  exercised  in  regard  to 
different  nutrient  materials  with  which  they  came  into  contact.  Al- 
though the  surrounding  media  might  contain  many  kinds  of  food,  yet 
cells  of  a  particular  kind  took  only  that  for  themselves  which  was  best 
adapted  to  their  wants,  disregarding  entirely  all  the  others.  As 
there  was  a  great  variety  of  cells,  there  must  necessarily  be  a  cor- 
responding variety  of  foodstuffs. 

What  is  true  of  the  cells  is  true  of  that  of  which  they  are  but 
components  or  units :  the  body.  Among  the  phenoniena  produced 
by  the  waste  of  the  solid  constituents  of  the  body  and  the  loss  of  the 
fluid  or  watery  parts  of  the  tissues  are  the  sensations  of  hunger  and 
thirst.  These  sensations  of  appetite  excite  the  desire  to  take  food, 
which  by  the  processes  of  digestion  is  prepared  for  absorption  and  cir- 
culation in  the  blood,  to  supply  the  various  needs  of  the  organism. 

The  term  food  includes  all  those  substances  received   into  the 
(24) 


CHEMICAL  CONSTITUENTS  OF  BODY  AND  FOOD.  25 

alimentary  canal  and  used /for  the  support  of  life,  by  supplying  the 
waste  continually  occurring  in  the  living  animal  tissues,  and  also 
weight,  heat,  and  energy.  Food  contains  substances  that  have  a  cer- 
tain chemical  relation  to  the  tissues  which  it  supports.  The  sub- 
stances out  of  which  the  complex  adult  tissues  are  constructed  are 
chemical  elements,  chemical  compounds,  or  unions  of  these  elements. 
The  food  taken  in  by  the  animal  consists  of  the  same  or  similar  com- 
position, in  its  nature  very  complex. 

Animals  are  either  carnivorous  or  herbivorous.  The  carnivora, 
or  flesh-eating  species,  consume  food  possessing  apparently  the  same 
chemical  components  as  the  tissues  and  fluids  of  their  own  bodies. 
The  food  of  the  herbivora,  or  vegetable-eating  species,  contains  prin- 
ciples resembling  very  closely  those  found  in  the  animal  body.  No 
matter  what  the  source  or  nature  of  the  food  for  animals  might  be, 
their  chemical  constituents  or  principles  are  similar,  since  it  is 
through  the  agency  of  the  vegetable  kingdom  with  the  aid  of  light 
and  heat  from  the  sun  that  the  simpler  combinations  of  inorganic 
nature  are  woven  together  and  elaborated  to  form  the  complex  organ- 
isms in  the  shape  of  plants  and  vegetables.  Thus,  the  animal  king- 
dom is  dependent  on  the  vegetable  for  its  existence ;  numerous  experi- 
ments have  proven  that  the  animal  organism  does  not  possess  the 
power  to  any  great  extent  of  constructing  complex  from  simple  mate- 
rials. Yet  complex  foods  it  must  have  to  supply  its  own  complex  con- 
stituents. However,  it  is  also  necessary  that  the  food  should  possess, 
besides  the  complex  constituents,  a  proper  proportion  of  the  various 
principles,  and  these  must  be  in  a  digestible  form.  It  is  well  known 
that  beans,  peas,  and  other  vegetables  contain  a  very  considerable 
percentage  of  proteid,  but  it  is  m  such  indigestible  form,  that  much 
of  it  passes  off  in  the  ftpces.  The  various  digestive  juices  had  been 
unable  properly  to  dissolve  their  nutritive  elements. 

Of  the  74  elements  known  to  the  chemist,  but  20  are  found  in 
the  body.  They  are:  carbon,  hydrogen,  nitrogen,  oxygen,  sulphur, 
phosphorus,  fluorin,  chlorine,  iodine,  silicon,  sodium,  potassium,  cal- 
cium, ammonium,  magnesium,  lithium,  iron,  and  occasionally  man- 
ganese, "Copper,  and  lead.  These  elements  are  rarely  found  in  the 
free  state,  being  usually  in  the  form  of  compounds. 

The  compounds,  or.  as  they  are  sometimes  termed,  proximate 
principles,  are  divided  into:  (1)  tnineral,  or  inorganic,  compounds; 
(2)  organic  compounds,  or  compounds  of  carbon.  The  organic  com- 
pounds may  again  lie  divided  very  conveniently  into  two  groups:  the 
nitrogenous  and  nonnitrogenous. 


26  I'lIVSIULOGY. 

The  inorganic  compounds  are  water;  the  various  acids,  sucli  as 
(he  hydrochhiric  acid  of  the  pistric  juice;  and  nunicrous  salts. 

Sinc(!  the  |)r().\imat('  principles  (if  Ixttli  food  and  tlie  hody  are 
the  same,  mention  of  the  princij)les  will  he  known  to  refer  to  hoth. 
A  very  convenient  method  of  grouping  the  principk's  of  hoth  food  and 
the  hody  is  that  hy  Hallihurton,  as  follows : — 


Inoiifiinic. 


Wafer. 

Sails,  as  oliloridos  .and  pliospliatos  of  sodium  and  falcium. 
Prolcids:  albumin,  myosin,  etc. 
Nitrogenous. ...  <(    Alhuminoids :  gelatin,  keratin,  etc. 

Bimpli'v  ')iilro(iriioiis  bodies:   lecilliin,  urea,  etc. 
I   Fats:  butter,  adipose  tissue. 
Nonnitrogenous  <^    Vaihohydratcs :  sugar,  starch. 

I    Hhiijdc  organic  bodies:  aleoliol,  lactic  acid. 

Although  all  (if  lliese  elements  are  })resent,  yet  not  all  are  of 
equal  importance  or  occur  in  the  same  proportions.  Among  the  inor- 
ganic group,  irater  and  mils  are  prominent;  among  the  organic,  car- 
huliy(Iraies\  fats,  and  proteids. 

WATER. 

Water  forms  more  than  one-half  of  the  hody-weight.  The  value 
of  water  to  the  economy  can  he  readily  appreciated  hy  the  student 
when  he  considers  that  the  various  processes  and  stages  of  digestion, 
absorption,  and  assimilation  are  dependent  upon  hydration  and  dehy- 
dration. About  fifty  ounces  of  urine  are  excreted  daily,  this  being 
the  main  avenue  for  the  escape  of  watery  elements  from  the  body. 
In  addition,  considerable  water  is  given  off  by  the  skin  as  sensible 
and  insensible  perspiration,  while  expired  air  is  heavily  laden  with 
moisture. 

With  so  much  water  making  its  escape  from  the  body,  at  least 
as  much  must  find  its  way  into  the  economy.  About  two  and  a  half 
quarts  of  water  are  ingested  daily  as  food.  The  water  we  drink  ought 
to  be  fresh,  limpid,  without  smell,  and  of  an  agreeable  taste.  When 
complete  and  exact  analysis  is  impossible,  the  taste  is  the  only  safe 
criterion  or  judge  as  to  its  fitness.  Drinking-water  should  always 
contain  a  certain  percentage  of  air.  The  palatability  is  due  to  the 
presence  of  carbonic  acid  gas  in  the  water.  Besides  gaseous  constitu- 
ents, solid  substances  are  also  present.  These  are  both  mineral  and 
organic,  and  should  be  present  in  but  very  small  amount. 


CHEMICAL  CONSTITUENTS  OF  BODY  AND  FOOD.  27 

Somewliat  more  water  is  excreted  daily  tlian  is  ingested,  since 
some  water  is  formed  in  tlie  tissues  by  the  oxidation  of  hydrogen. 

SALTS. 

The  most  important  salts  fonnd  are  the  sulphates  and  chlorides 
of  sodium;  the  phosphates  of  sodium,  potassium,  calcium,  and  mag- 
nesium; and  the  carbonates  of  sodium  and  calcium. 

Of  these  various  salts,  sodium  chloride  is  the  most  important 
and  the  most  common  one  found.  In  the  fluids — blood,  serum, 
lymph,  and  urine — this  salt  is  high  in  percentage.  While  in  the 
body  it  favors  aljsorption  by  increasing  the  endosmosis  of  the  tissues 
and  so  aids  metabolic  processes,  the  absence  of  sodium  chloride  for 
an  extended  time  causes  disturbances  and  disorders  in  the  constitu- 
tion. There  are  about  3000  grains  of  common  salt  present  in  the 
body.  About  180  grains  are  excreted  daily  in  the  urine,  wdiile  some 
finds  its  exit  as  a  component  of  the  faeces,  sweat,  and  tears. 

A  practical  illustration  of  its  value  to  animal  life  may  be  gained 
by  noticing  how  wild  animals  repair  to  the  so-called  '^salt  licks"  at 
various  times,  traveling  for  many  miles  to  procure  it. 

The  Africans  in  the  interior  of  their  country  do  not  have  NaCl, 
but  use  the  ashes  of  certain  plants.  These  ashes  chiefly  contain  KCl 
and  K2SO4  and  one-twentieth  per  cent,  of  sodium  salts. 

Calcium  phosphate  is  a  very  prominent  factor  of  the  mineral 
solids  of  the  body.  It  forms  about  one-half  of  the  bony  skeleton. 
where  it  is  most  abundant,  although  it  occurs  to  some  extent  in  all 
other  solids  and  fluids.     This  salt  is  particularly  conspicuous  in  milk. 

Iron  is  an  important  element  of  hemoglobin.  It  is  this  iron 
in  the  red  blood-corpuscles  that  is  the  means  of  holding  the  oxygen 
without  being  itself  oxidized.  A  want  of  it  causes  the  pathological 
condition  called  anemia.  In  the  blood  of  an  adult  are  found  forty- 
five  grains.  In  small  proportions  it  is  found  in  the  liquids  of  the 
body, — as  the  chyle,  lymph,  bile,  urine,  etc., — in  the  feces,  and  traces 
in  the  liver  and  spleen. 

I.  CARBOHYDRATES. 

Tlie  car])ohydrates  are  found  principally  in  the  vegetable  king- 
dom. They  are,  however,  not  indigenous  to  the  vegetable  kingdom, 
but  are  found  and  formed  in  animal  tissues ;  notably,  glycogen,  or 
animal  starch;  dextrose;  and  lactose,  or  milk-sugar. 

For  the  sake  of  a  clearer  conception  of  the  term  carbohydrate  the 
components  of  the  name  are  used  when  it  is  defined  as  a  compound  of 


28  PHYSIOLOGY. 

carbon,  hydrogen,  and  oxygen,  the  last  two  in  tlie  proportion  occurring 
in  the  formation  of  water,  two  to  one. 
The  carboliydrates  are: — 

Glucoses  (CgHjaOe),  or  monosaccharides. 

Saccharoses  (C12  H22  On),  or  disaccharides. 

Amvloses  (CcHkjO-),  or  polysaccharides. 
The  Glucoses  are  glucose;  or  dextrose,  or  grape-sugar;  Igevulose, 
and  galactose.  The  glucoses  have  three  properties  which  are  im- 
portant for  the  physiologist  to  know:  physical,  chemical,  and  bio- 
logical. From  the  fact  that  it  deviates  the  plane  of  polarization  to 
the  right,  its  physical  property  is  demonstrated,  whence  its  name, 
dextrose.  Its  chemical  property  is  the  reducing  of  certain  metallic 
salts  in  the  presence  of  alkalies.  Biologically,  it  ferments  under  the 
influence  of  the  zymase  of  yeast  to  form  carbonic  acid  and  ethylic 
alcohol.  The  zymase,  an  intracellular  ferment,  is  formed  in  the  body 
of  the  cell. 


Fig.  5. — Yeast  Fungus.      (After  Harley.) 

Saccharoses. — The  saccharoses  are  saccharose,  or  cane-sugar;  lac- 
tose, or  milk-sugar;  and  maltose.  When  saccharose,  or  cane-sugar, 
is  boiled  with  a  dilute  mineral  acid,  the  right-handed  polarizing  solu- 
tion of  saccharose  is  transformed  into  invert-sugar,  or  is  said  to  be 
inverted.  Invert-sugar  is  a  mixture  of  equal  weights  of  glucose,  a 
right-handed  polarizing  agent,  and  Isevulose,  which  is  a  left-handed 
polarizing  body.  The  saccharoses  do  not  reduce  the  copper  salts. 
The  saccharoses  are  not  directly  fermentable  by  yeast  except  in  this 
way :  ( 1 )  when  yeast  is  added,  the  saccharoses  take  up  water  and  the 
soluble  ferment  of  yeast,  invertin,  changes  the  saccharoses  into  glu- 
cose and  laevulose;  then  (2)  the  zymase  fermentation  of  the  glucose 
and  laevulose  by  the  yeast-cell,  which  is  not  a  vital  act. 

Lactose,  or  sugar  of  milk,  is  a  right-handed  polarizing  sugar.  It 
reduces  the  copper  salts,  but  is  not  fermentable  either  directly  or  in- 
directly by  the  yeast-ferment.  Lactose  ferments  in  the  presence  of 
the  lactic  acid  bacillus  to  form  lactic  acid. 

Maltose  is  a  right-hand  polarizing  sugar,  reduces  copper  salts, 


CHEMICAL  CONSTITUENTS  OF  BODY  AND  FOOD.  29 

and  ferments  by  yeast.  Maltose  has  the  same  properties  as  glucose, 
but  is  distinguished  in  two  ways:  (1)  the  light-rotating  power  of 
glucose  is  56  degrees,  while  maltose  is  150  degrees;  (2)  the  reducing 
of  metallic  salts  by  glucose  is  equal  to  100,  while  that  of  maltose  is 
but  66.     The  sugar  in  blood  is  a  glucose. 

By  moistening  barley  and  germinating  it  in  heaps  at  a  constant 
temperature,  the  starch  of  the  barley  is  converted  into  dextrose  and 
maltose.  This  change  is  brought  about  by  the  ferment  called  dias- 
tase, which  is  found  in  barley.  This  product,  when  dried,  is  denom- 
inated malt,  which,  when  it  is  acted  upon  by  yeast,  produces  the 
malted  beverages,  beer  and  ale.  Maltose  by  invertin  of  yeast  is 
changed  into  glucose. 

Amyloses,  or  Polysaccharides. — Under  the  influence  of  dilute 
mineral  acids  the  amyloses  are  changed  by  boiling  or  are  transformed 
into  glucose.  Starch  presents  a  polarizing  cross:  black  cross  upon 
a  white  ground  or  a  white  cross  upon  a  black  ground.  Starch  does 
not  reduce  copper  solution  nor  is  it  fermentable  by  yeast.  When 
iodine  is  added  to  starch  it  gives  a  blue  color. 

Glycogen,  or  animal  starch,  does  not  reduce  copper  salts  nor  is 
it  fermentable  by  yeast.  During  the  hydrolysis  of  starch  dextrin  is 
formed  as  an  intermediate  product.  Dextrins  colored  red  l^y  iodine 
are  called  erythrodextrins ;  those  not  colored  by  iodine  are  called 
achroodextrins. 

2.  FATS. 

Fats  form  a  more  or  less  variable  proportion  of  the  animal 
economy.  They  come  to  us  principally  in  the  form  of  animal  food, 
but  to  some  extent  in  vegetable  food,  also,  especially  in  seeds,  nuts, 
fruit,  and  roots. 

The  fats  contain  in  their  substances  a  fatty  principle  having 
acid  properties — a  sort  of  fatty  acid.  When  acted  upon  by  alkalies 
and  ferments,  this  acid  becomes  separated  and  a  sweet  principle 
known  as  glycerin  makes  its  appearance.  Thus  fats  may  be  said  to 
be  compounds  of  fatty  acids  with  glycerin.  It  would  seem,  however, 
that  the  glycerin  had  not  pre-existed  in  the  fats,  as  the  united  weight 
of  the  glycerin  and  the  fatty  acid  produced  exceeds  that  of  the  fat 
originally  employed. 

In  bone-marrow,  adipose  tissue,  and  milk,  the  fats  are  very 
prominent  components.  The  adipose  tissue  consists  of  nucleated 
vesicles  filled  with  fatty  matter.  The  vesicles  are  closely  packed 
together  and  are  surrounded  by  a  network  of  blood-vessels  which 


30  PHYSIOLOGY. 

draw  out  from  this  source  a  supply  for  nutrition.  This  fatty  tissue 
is  found  between  the  muscles,  bones,  vessels,  etc.,  and,  by  its  accumu- 
lation under  the  skin,  gives  to  the  surface  of  the  body  its  full  and 
regular  outline. 

By  reason  of  its  bad  conducting  power,  it  helps  to  keep  the 
various  structures  of  the  body  warm  by  a  coating  of  it  lying  under 
the  skin.  This  fact  is  best  illustrated  in  warm-blooded  aquatic  ani- 
mals, such  as  the  seal,  porpoise,  or  whale. 

The  normal  fats  found  in  the  body  and  used  for  food  are  divided 
into  three  compounds :     stearin,  palmitin,  and  olehi. 

Stearin  is  the  most  solid  of  the  three.  It  is  typically  illustrated 
in  mutton  suet,  and  is  the  element  which  makes  this  fat  so  hard  and 
firm,  and  characterizes  it  at  once.  Its  melting-point  is  145°  F.,  so 
that  at  ordinary  temperatures  it  is  solid. 

Palmitin  occupies  a  position  midway  between  stearin  and  olein 
as  regards  consistency.  It  is  the  principal  constituent  of  most  animal 
fats,  and  occurs  largely  in  vegetable  fats  also. 

Olein  is  always  found  in  a  fluid  state  unless  the  temperature  be 
very  low.  When  the  olein  ingredients  predominate  in  a  body  it  is 
then  in  a  liquid  state,  as  in  the  case  of  the  oils.  Olein  is  found  in 
both  animal  and  vegetable  fats,  but  the  vegetable  fats  are  richer  in  it 
than  the  animal.  The  oils  used  in  food — olive-oil,  oil  of  sweet 
almonds,  etc. — are  derived  from  the  vegetable  kingdojn. 

Human  fat  contains  about  75  per  cent,  of  olein  plus  a  small 
quantity  of  fatty  acids  in  a  free  state.  All  are  soluble  in  hot  alcohol, 
ether,  and  chloroform,  but  insoluble  in  water. 

Saponification. 

When  fat  is  boiled  with  alcoholic  soda  or  potash,  the  particles  of 
fat  are  broken  up  into  a  small  quantity  of  glycerin  and  a  large  quan- 
tity of  fatty  acid.  The  fatty  acid  unites  with  the  soda  or  potash, 
forming,  as  a  result,  soap.  This  process  of  soap-forming  is  known  as 
saponification. 

Emulsification. 

If  oil  and  water  are  well  shaken  together  the  fatty  particles  do 
not  form  a  part  of  the  water,  but  are  held  in  suspension  and  come 
to  the  surface  in  the  form  of  small  globules.  A  mixture  of  an  oil, 
a  soap,  and  water  is  spoken  of  as  an  emulsion.  No  emulsion  is  per- 
manent, for  even  in  milk,  the  most  perfect  of  emulsions,  the  fatty 
particles  in  the  form  of  cream  rise  to  the  surface  in  a  few  hours. 


CHEMICAL  CONSTITUENTS  OF  BODY  AND  FOOD.  31 

Emulsification  is  a  physical  or  mechanical  rather  than  a  chemical 
change.  Both  soaps  and  emulsions  are  continually  being  formed  in 
the  body  during  the  digestion  of  fats. 

3.  PROTEIDS,  OR  PROTEINS. 

The  principal  constituents  forming  the  muscular,  nervous,  and 
glandular  tissues,  as  well  as  the  serum,  blood,  and  lymph,  are  proteids. 
In  normal  urine  there  are  found  no  proteids,  or,  if  any,  only  traces. 
In  a  great  measure  the  various  phenomena  of  life  are  present  and  due 
to  the  protoplasm  in  the  cells.  On  analyzing  protoplasm  chemically 
its  substance  is,  of  course,  killed  by  the  reagents  used,  but  proteids 
invariably  result  in  the  process.  Whether  the  proteids  exist  as  such 
in  the  protoplasm,  or  occur  only  after  the  death  of  the  protoplasm, 
has  not  been  fully  established,  but  they  are  believed  to  be  the  con- 
stituents of  it.  However,  none  of  the  phenomena  of  life  occur  with- 
out their  presence. 

Proteids  are  very  complex,  comprising  compounds  of  carbon, 
hydrogen,  nitrogen,  oxygen,  and  sulphur.  They  may  be  either  solid 
or  liquid,  as  they  are  found  in  the  different  tissues  of  the  body.  The 
different  classes  of  proteids  present  both  physical  and  chemical  pecu- 
liarities, although  all  have  certain  common  reactions.  Some  are  sol- 
uble, others  are  insoluble,  in  water,  while  nearly  all  are  soluble  in 
ether  and  alcohol.  Strong  acids  and  alkalies  are  also  capable  of  dis- 
solving the  proteids.  but  in  the  process  of  dissolution  decomposition 
almost  invariably  occurs. 

The  supply  of  proteids  in  our  bodies  is  obtained  from  the  vege- 
table kingdom,  being  taken  in  as  vegetables  directly,  or  indirectly  in 
the  form  of  meat  which  is  derived  from  animals  that  live  on  vege- 
tables. Thus  the  proteids  are  built  up  from  the  simpler  inorganic 
compounds  taken  from  the  soil  and  air  and  elaborated  in  plant-struc- 
ture. 

The  chemical  composition  of  the  proteids  is  variable,  depending 
upon  the  products  analyzed  by  the  different  investigators,  as  the 
purity  of  the  substances  cannot  be  definitely  determined.  From  in- 
vestigations we  have  the  following  average  percentages:  0,  21.50  to 
23.50;  H,  6.5  to  7.3;  K,  15.0  to  17.6;  C,  50.6  to  54.5;  S,  0.3  to  2.2. 

The  nitrogen  and  sulphur  are  each  contained  in  the  molecule  in 
two  forms,  the  one  loosely  combined,  the  other  firmly  combined. 
The  basis  of  construction  of  all  proteids  is,  according  to  Kossel.  a 
body  called  protamin  (C3oH.-N"i-Og),  which  on  hydrolysis  gives  three 
basic  substances  each  containing  six  carbon  atoms,  hence  called  hexone 


32  PllYSJULUCiY. 

bases,  lysin,  histidin,  and  arginin.  Protamin  has  been  found  loosely 
combined  with  nucleic  acid  in  the  spermatozoa  of  fishes.  In  the  pro- 
teid  molecule  it  is  firmly  combined  with  the  amido  acids,  like  leucin, 
glycin,  and  usually  with  tlie  aromatic  bodies,  like  tyrosin,  etc.,  and  in- 
organic elements,  like  sulphur  and  phosphorus.^ 

The  proteids  of  different  animals  seem,  to  rough  chemical  tests, 
to  be  the  same;  but  the  precipitin  test  shows  a  difference  between 
tliem.  The  casein  of  cow's  milk  is  not  exactly  similar  to  that  of 
wonum's  milk. 

More  is  required  than  a  mere  equivalent  of  nitrogen  to  cover  the 
loss  of  nitrogen  from  the  body. 

Polypeptids. 

When  proteids  are  split  up  by  either  ferments  or  chemical 
agents,  the  general  order  of  the  products  is  the  same.  Tlie  first 
action  is  to  produce  proteids  which  have  smaller  molecules  than  the 
original  native  albumin.  These  products  are  denominated  albu- 
moses.  The  next  stage  is  the  formation  of  still  smaller  molecules  of 
peptone,  and  finally  the  peptone  breaks  up  into  smaller  crystalline 
materials  of  known  composition,  which  do  not  give  typical  proteid 
reactions.     The  above  chemical  reactions  are  hydrolyses. 

These  bodies  can  be  arranged  into  groups : — 

(1)  Monoamino  acids,  such  as  glycin  or  glycocoll,  leucin,  aspar- 
tic  acid,  glutaminic  acid,  etc. 

(2)  Diamine  acids,  as  lysin,  arginin,  valeric  acid,  containing  a 
urea  radical  like  creatin  and  histidin.  The  introduction  of  a 
second  amino  or  NH.  group  confers  basic  properties  upon  the  acid ; 
hence  the  name  hexone  bases — hexone  because  all  contain  six  atoms  of 
carbon. 

(3)  Aromatic  amino-acids,  such  as  phenylalanin,  tyrosin.  and 
tryptophan,  the  mother  substance  of  indol  and  skatol. 

(4)  Pyrimidin  bases,  such  as  thymin  (cytosin)  and  pyrroli- 
din  derivatives. 

(5)  The   sulphur-containing  substance,   cystin. 

(6)  Ammonia. 

The  amido-acids  have  been  shown  by  Fischer  to  possess  the  prop- 
erty of  combining  with  one  another  to  nuike  complex  molecules  con- 


^  Beddard,  "Practical  Physiology'." 


CHEMICAL  CONSTITUENTS  OF  BODY  AND  FOOD.  33 

taining  two,  three,  or  more  groups  of  amido-acids.  Thus,  two  mole- 
cules of  amido-acid  (glycocoll)  may  be  made  to  unite  to  form  a  com- 
pound, glycylgljcin,  which  Fischer  calls  a  peptid.  When  formed 
from  the  union  of  two  amido-acids,  they  are  called  dipeptids;  from 
three,  tripeptids;  from  more  complicated  compounds  of  this  kind, 
the  polypeptids,  which  have  a  reaction  similar  to  that  of  proteids. 
The  polypeptids  occupy  in  proteolysis  a  stage  between  the  peptones 
and  the  final  simpler  amido-acids,  and  can  be  found  in  peptic  and 
tryptic  digestion  of  albumin. 

^Ye  may  write  the  formulaa  for  the  three  typical  amino-acids  as 
follows : — 

Glycin— HNH,  CH,,  COOH  (amino-acetic  acid). 

Alanin — HXH,  C.H^.  COOH   (amino-propionic  acid). 

Leucin — HXH,  CgH^o,  COOH  (amino-caproic  acid). 

In  each,  the  first  and  last  groups  are  the  same,  the  middle  group 
varies  and  may  l)e  represented  by  E.  The  general  formula  of  the 
mono-amino  acids  is.  therefore:     HNH,  E,  COOH. 

If  now  we  link  these  two  together,  we  get  HXH,  E,  CO, 
|0H  H|  NH,  E,  COOH.  What  happens  is  that  tlie  hydroxyl 
(OH)  of  the  carboxyl  (COOH)  group  of  one  acid  unites  with  one 
atom  of  the  hydrogen  in  the  next  amino  (HXH)  group,  and  water 
is  thus  formed,  as  shown  in  the  oblong,  and  the  rest  of  the  chain 
closes  up  and  the  water  is  eliminated.  In  this  way  we  get  a  dipep- 
tid.  The  names  glycyl,  alanyl,  leucyl.  etc.,  are  given  by  Fischer  to 
the  XH2,  E,  CO  groups  which  replace  the  hydrogen  atom  of  the 
nexb  XH,  group.^ 

Thus :  glycyl-glycin,  glycyl-leucin,  leucyl-alanin,  alanyl-leucin, 
and  numerous  other  combinations  and  permutations  are  obtained. 

If  the  same  operation  is  repeated,  we  obtain  tripeptids  (leucyl- 
glycyl-alanin,  alanyl-leucyl-tyrosin,  etc.)  ;  then  we  have  the  tetra- 
peptids  and  so  on ;  and  in  the  end,  by  coupling  the  chains  sufficiently 
often  and  in  appropriate  order,  Fischer  has  already  obtained  sub- 
stances which  give  the  reaction  of  a  peptone. 

Hence  we  may  consider  proteids  as  essentially  polypeptid  com- 
pounds of  greater  or  less  complexity ;  that  is,  they  are  acid-amids 
formed  by  the  union  of  a  number  of  amido-acid  compounds.  Many 
of  the  polypeptids  have  l)cen  produced  synthetically,  and  these  facts 
lead  to  the  hope  that  the  actual  synthesis  of  the  proteid  molecule 
may  be  finally  accomplished. 


British  ^Medical  Journal. 


34  PHYSIOLOGY. 

Classification    of   Proteids    or    Proteins. 

For  tlic  sake  of  convenience  and  study  the  proteids  have  been 
divided  into  various  groups  and  classes  by  dill'erent  autliorities.  They 
are  almost  universally  divided  into  the  two  niain  <;r()U})s  of  animal 
and  vegetable  origin.  Tbe  amount  of  proteid  matter  in  plants,  par- 
ticularly the  full-grown  ones,  is  less  than  in  animals.  It  is  found  dis- 
solved in  their  juices,  in  the  protoplasm,  or  deposited  in  the  form  of 
grains  called  aleuron  granules.  Vegetable  proteids  are  divisible  into 
the  same  classes  as  the  animal,  but,  since  human  physiology  deals 
with  animal  proteids,  the  vegetables  are  disregarded. 

A  convenient  classification  is:  (1)  native  albumins,  (2) 
derived  albumins,  or  albuminates,  (3)  compound  proteids,  (4)  globu- 
lins, (5)  peptones,  (6)  albuminoids,  (7)  histons,  and  (8)  protamins. 

I.  Native  Albumins. 

The  proteids  of  this  class  are  those  that  are  found  in  an  unal- 
tered, natural  state  or  condition  in  the  solids  of  the  body.  They  are 
soluble  in  water  and  are  not  precipitated  by  the  dilute  acids.  The 
two  main  forms  are  egg-albumin  and  serum -albumin.  The  egg- 
albumin  occurs  in  the  part  of  the  egg  known  as  tlie  white.  The 
serum-albumin  is  found  not  only  in  the  blood-serum,  but  also  in  the 
lymph  as  it  is  found  in  its  proper  lymphatic  channels  and  diffused 
throughout  the  tissues,  in  the  chyle,  milk,  and  transudations. 

2.  Derived  Albumins,  or  Albuminates,  or    Meta=proteins. 

To  this  class  belong  two  divisions:  acid-albumin  and  all-ali- 
albumin. 

The  derived  albumins  are  formed  from  the  native  albumins  by 
the  action  of  weak  alkalies  or  acids.  Thus,  when  a  native  albumin, 
such  as  serum-albumin,  is  treated  for  a  while  with  dilute  hydro- 
chloric acid  its  properties  become  entirely  changed.  The  solution  is 
no  longer  able  to  be  coagulated  by  heat,  and  when  the  solution  is  care- 
fully neutralized  the  whole  of  the  proteid  is  thrown  down  as  a  pre- 
cipitate. The  substance  into  which  the  native  albumin  was  changed 
by  the  action  of  an  acid  is  called  an  acid-albumin,  or  s\Titonin.  This 
acid-albumin  is  insoluble  in  distilled  water  and  neutral  saline  solu- 
tions, but  readily  soluble  in  dilute  acids  and  alkalies.  This  is  the 
process  through  which  albumins  pass  when  undergoing  gastric  diges- 
tion and  when  acted  upon  by  the  HCl  of  the  gastric  juice. 


CHEMICAL  CONSTITUENTS  OF  BODY  AND  FOOD.  35 

If  serum-albumin,  egg-albumin,  or  washed  muscle  is  acted  on  by 
an  alkali,  instead  of  an  acid,  the  proteid  undergoes  changes  similar  to 
those  i^roduced  by  the  acid,  except  that  the  product  formed  is  an 
alkali-albumin  instead  of  an  acid  one. 

3.   Compound  Proteids,  Conjugated   Protein,  or  Proteides  of  Germans. 

These  are  native  proteids  with  another  organic  substance,  in 
contrast  to  albuminates,  which  are  compounds  of  native  proteids 
with  inorganic  substances.  The  compound  proteins  include  (1) 
glucoproteins.  like  mucin,  consisting  of  a  proteid  combined  with  a 
carbohydrate  group;  (2)  nucleoproteins  are  built  up  of  albumins, 
nucleic  acid,  and  always  contain  iron.  They  exist  in  the  cell-nu- 
cleus; (3)  phosphoproteins,  like  casein  of  milk  and  vitellin  of  yelk 
of  eggs;   (4)   chromoproteins,  like  haemoglobin. 

Tests  for  Proteids. —  (A)  Color  Tests. —  (1)  The  biuret  test 
of  Eose  and  Wiedemann, — when  a  solution  of  albumin  is  made 
strongly. alkaline  with  caustic  potash,  and  a  solution  of  copper  sulphate 
is  added  drop  by  drop,  then  a  pink-violet  color  is  produced. 

(2)  The  xanthoproteic  test  of  Fourcroy  and  Yauquelin.  Add 
nitric  acid,  and  a  white  precipitate  ensues,  which,  on  being  boiled, 
turns  yellow ;  on  cooling,  add  ammonia ;  the  yellow-colored  precipitate 
becomes  orange.  This  reaction  depends  upon  the  presence  of  the 
benzol  ring  in  the  proteid  molecule  (phenylalanin,  tyrosin,  indol).. 

(3)  Millon's  reagent.  This  reagent  is  a  solution  of  mercuric 
nitrate  in  -water  containing  free  nitrous  acid.  On  adding  it  to  a 
solution  of  albumin,  a  whitish  precipitate  ensues,  which  becomes  a 
brick-red  on  boiling.  This  reaction  indicates  the  presence  of  oxy- 
phenol  group   (tyrosin). 

(B)  Precipitation  of  Proteids  by  I^eutral  Salts. —  (1) 
Saturation  with  ammoniimi  sulphate  precipitates  all  proteids  except 
peptones. 

(C)  Precipitatio>t  of  Proteids  by  Acids. —  (1)  Add  a  drop 
or  two  of  strong  nitric  acid,  a  white  precipitate  ensues. 

4.   Globulins. 

The  globulins  are  quite  abundant.  The  globulins  differ  from 
the  albumins  in  that  they  are  not  soluble  in  distilled  water.  There 
must  be  present  an  appreciable  amount  of  sodium  chloride  or  mag- 
nesium sulphate. 

Globulins  are  insoluble  in  saturated  solution  of  all  the  neutral 


86  PHYSIOLOGY. 

salts.  They  are  also  insoluble  in  a  half-saturated  solution  of  ammo- 
nium sulpluite.     They  are  coagulated  by  heat. 

The  different  members  of  this  group  are :  serum-globulin  (para- 
(jlohuVm),  and  pbrinugcn  in  blood,  myusmogen  in  muscle,  etc. 

I'araglobulin  is  a  ])recipitate  that  can  be  formed  from  blood- 
serum  by  diluting  it  tenfold  with  water,  and  passing  through  it  a 
current  of  carbon  anhydride.  A  flocculent,  and  finally  a  granular, 
precipitate  results,  which  is  the  paraglobulin. 

The  coagulated  proteids  are  fibrin,  myosin,  and  casein.  The 
coagulation  is  produced  by  ferments. 

Fibrinogen  is  present  in  the  blood,  chyle,  serous  fluids,  'and 
transudations. 

Myosinogen  is  the  principal  proteid  found  in  muscle. 

5.  Peptones. 

In  the  body  peptones  are  the  final  results  of  the  action  of  the  gas- 
tric and  pancreatic  juices  upon  the  native  proteids,  and,  as  peptones, 
are  ready  for  absorption  by  the  cells.  Although  formed  in  large 
quantities  in  the  stomach  and  intestine,  they  are  absorbed  as  soon 
as  formed,  since  none  are  left  in  these  organs.  Peptones  can,  how- 
ever, be  produced  outside  the  body  by  the  action  of  dilute  acids  at 
medium  temperatures. 

The  peptones  are  soluble  in  water,  not  coagulated  by  the  pres- 
ence of  heat,  cannot  be  precipitated  by  the  usual  proteid  precipitants, 
and  diffuse  very  readily  through  membranous  tissues. 

Siegfried  has  recently  isolated  peptones  of  a  basic  character  by 
hydrolysis  of  all)umins  with  about  12  per  cent,  of  hydrochloric  acid. 
He  calls  these  bodies  kyrines. 

Intermediate  products  between  the  native  proteids  and  peptones 
are  the  proteoses.  True  peptones  are  not  found  in  the  circulating 
juices  of  plants,  but  the  product  found  is  very  likely  proteose. 

The  proteoses  are  only  slightly  diffusible,  they  are  not  coagulated 
by  heat,  but  can  lie  precipitated.  A  characteristic  feature  of  their  pre- 
cipitates is  that  they  can  be  dissolved  by  heating,  but  reappear  when 
the  solution  cools. 

6.  Nitrogenous  Bodies  Allied  to   Proteids,   or   Albuminoids,   or  Sclero= 

proteins. 

Besides  the  proteids  there  are  other  nitrogenous,  noncrystalline 
bodies  that  are  allied  to  the  former,  having  many  general  points 
in  common. 


CHEMICAL  CONSTITUENTS  OF  BODY  AND  FOOD.  37 

Gelatin  is  the  substance  produced  by  heating  in  dilute  acetic  acid 
for  several  days,  the  collagen  of  connective-tissue  fibers.  It  possesses 
the  property  of  setting  into  a  jelly  when  its  concentration  is  greater 
than  1  per  cent.  When  digested  it  is  converted  into  a  peptone,  and, 
although  readily  absorbed,  is  not  a1)le  to  take  the  place  of  a  true 
proteid,  since  it  cannot  build  up  nitrogenous  tissue,  being  valuable 
only  as  a  means  of  storing  up  energy. 

Keratin  is  the  horny  material  forming  the  outer  layer  of  the 
epidermis,  hair,  wool,  nails,  hoofs,  etc. 

Elastin  of  elastic  tissue  belongs  to  this  group. 

7.  Histones. 

To  the  histones  belong  globin,  the  proteid  which  is  separated 
from  hammglobin  by  decomposing  acids  and  alkalies. 

8.   Protamins. 

The  protamins  are  salmin,  clupein,  scombrin,  sturin,  etc. 

ALIMENTARY  SUBSTANCES. 

We  have  learned  that  the  body  is  composed  of  the  chemical  con- 
stituents or  proximate  principles,  carbohydrates,  fats,  and  proteids 
comprising  the  organic  group,  and  water  and  salts  the  inorganic  class. 
In  order  that  the  nutrition  of  the  body  may  proceed  normally,  it  is 
very  apparent  that  those  principles  must  be  supplied  in  the  food,  in 
the  proper  proportions  and  quantities.  So,  a  proper  diet  for  man  is 
one  containing  the  proximate  principles  in  their  ])roper  proportions, 
the  value  of  it  depending  mainly  on  the  amount  of  carbon  and  nitro- 
gen present. 

The  elements,  as  elements,  are  not  valual)le;  it  is  only  when 
they  are  in  combination  that  they  serve  their  proper  ends  as  foods. 
For  the  elements,  to  constitute  an  organic  product,  must  be  united 
previously  by  some  living  organism.  It  is  not  often  that  the  alimen- 
tary substances  are  used  by  us  as  Nature  furnishes  them,  even  though 
they  contain  the  proper  ingredients.  One  requisite  is  that  they 
should  be  presented  in  a  digestible  form.  Water,  heat,  and  condi- 
ments are  the  three  agents  used  to  make  food  more  palatable  and 
digestible.  Water  helps  to  soften  the  insoluble  substances,  and 
to  dissolve  the  principal  substances.  Heat  modifies  the  foods 
still  more,  so  that  they  acquire  different  cliaracters.  Condiments 
give  physical  satisfaction  and  enjoyment,  and,  at  the  same  time,  they 
please  the  taste. 


38  PHYSIOLOGY. 

A  diet,  to  be  sufficient,  must  be  adapted  to  tlie  particular  indi- 
vidual's need,  keeping  in  mind,  also,  the  climate,  age  of  person,  and 
the  amount  of  work  done  by  him. 

We  make  changes  of  clothing  to  suit  the  weather  conditions  in 
order  that  the  body  may  not  suffer  in  regard  to  the  surrounding  tem- 
perature, and  our  diet  should  be  regulated  with  the  same  ends  in 
view.  In  cold  weather  we  eat  more,  to  furnish  an  extra  amount 
of  heat;  in  warm  weather  we  eat  less  than  usual.  A  growing  youth's 
body  must  not  only  repair  the  daily  waste,  but  also  assist  in  con- 
structive metamorphosis,  or  growth,  so  that  he  requires  relatively 
more  food  per  diem  than  the  adult.  Because  of  the  waste  attending 
action,  the  workingman  requires  more  than  the  ordinary  supply  of 
food. 

There  are  some  single  foods  which  contain  all  the  necessary 
proximate  principles  in  proper  proportions,  but  they  are  the  excep- 
tions, rather  than  the  rule.  Thus  milk  and  eggs  are  classed  as  per- 
fect foods.  It  is  usually  necessary  for  a  proper  diet  to  contain  a  vari- 
ety of  substances  in  this  list. 

For  a  man  doing  a  moderate  amount  of  work,  it  has  been  com- 
puted that  it  is  necessary  that  the  daily  diet  should  contain  the  fol- 
lowing amounts  :— 

Proteid    125  grams. 

Fat ; 50  grams. 

Carboliydrates    500  grams. 

Alimentary  substances  comprise  products  of  both  animal  and 
vegetable  kingdoms.  The  principal  ones  are  animal  substances,  with 
cereals,  potatoes,  drinks,  condiments,  cocoa,  coffee,  tea,  etc. 

The  animal  substances,  or  foods,  comprise:  (1)  meat,  (2) 
eggs,  and   (3)   milk,  with  its  derivatives — cream,  butter,  and  cheese. 

The  parts  of  animals  used  for  food  are  the  various  portions  of 
their  muscular  system.  They  comprise  the  general  term  meat.  Ani- 
mal food.  1:)eing  identical  with  the  body  structures,  requires  nothing 
to  be  added  or  subtracted  to  make  it  fit  to  give  proper  nourishment. 

MEAT. 

The  more  compact  the  fiber,  the  less  digestible  the  meat.  Hence 
ham  is  much  less  digestible  than  other  meats.  The  more  fat  that  is 
combined  intimately  with  the  fibers,  so  much  less  is  the  digestibility 
of  the  meat,  because  the  fat  melts  and  coats  the  fibers  of  the  meat 
with  a  layer  of  oil  which  prevents  the  ferment  from  acting  upon  it. 


CHEMICAL  CONSTITUENTS  OF  BODY  AND  FOOD.  39 

Meat  is  noted  for  the  large  quantity  of  nitrogenous  matter  which  it 
contains,  containing  four  times  the  amount  of  proteid  compared  with 
the  same  weight  of  milk.  The  proteid  in  meat  is  myosin,  the  main 
constituent. 

Beef-tea  is  a  solution  of  gelatin,  salts,  extracted  matters,  a  little 
albumin,  together  with  some  fat.  The  value  of  beef-tea  as  an  ali- 
mentary substance  has  been  much  disputed,  some  claiming  great 
results  from  it,  others  none.  However,  one  thing  is  certain;  it 
possesses  a  stimulant  and  restorative  value,  though  it  must  not  be 
depended  iipon  as  a  food  and  administered  as  such. 

Liebig's  Beef  Tea. — It  contains  novain,  oblitin,  ignotin,  and 
neosin.  Oblitin  increases  the  tonus  and  peristaltic  movements  of 
the  intestine.  It  also  increases  the  salivary  secretion  and  lowers 
arterial  tension.  Novain  has  a  similar  action  to  oblitin.  Neosin 
lowers  the  arterial  tension.  Neosin  is  also  obtained  from  fresh  muscle, 
and  is  not  due  to  putrefactive  changes  in  beef-tea. 

The  process  of  cooking  meat  loosens  up  the  various  fasciae  and 
enveloping  membranes,  thereby  separating  the  fibers;  at  the  same 
time  parasitic  growths  are  killed.  Thus  the  digestive  juices  are  given 
more  ample  opportunity  for  acting  upon  all  parts  of  the  foods,  even 
penetrating  into  the  innermost  parts. 

EGGS. 

The  white  of  an  egg  is  a  faint-yellowish,  albuminous  fluid  in- 
closed in  a  framework  of  thin  membranes,  and  this  fluid  itself  is  very 
liquid,  but  seems  viscid,  because  the  membranes  are  entangled.  Oval- 
bumin, or  the  egg-albumin  of  the  egg-white,  is  the  chief  constituent. 
The  mineral  bodies  in  the  white  of  the  egg  are  potash,  soda,  lime, 
magnesia,  iron,  chlorine,  phosphoric  acid,  and  sulphuric  acid. 

The  principal  part  of  the  yelk  is  an  orange-yellow,  alkaline  emul- 
sion of  a  mild  taste.  Tlie  yelk  contains  vitellin  as  its  principal  con- 
stituent. Besides  vitellin,  the  yelk  contains  alkali  albuminate  and 
albumin.  The  yelk  also  contains  a  phosphorized  fat  (lecithin)  with 
cholesterin,  fats,  and  a  small  quantity  of  sugar  and  of  mineral  bodies, 
chiefly  lime  and  phosphoric  acid.  Iron  exists  in  the  yelk  in  an  or- 
ganic combination. 

As  the  egg  is  so  easily  digested  it  is  prized  highly  as  a  food. 
However,  the  more  that  an  egg  is  boiled,  the  more  insoluble  do  the 
proteids  become  and  so   are   more  indigestible. 

In  cases  where  eggs  are  difficult  of  digestion  the  white  of  egg 
may  be  given.     In  some  persons  the  yelks  of  eggs  cause  headache  and 


40 


PHYSIOLOGY. 


drowsiness.     The  caloric  value  of  two  eggs  is  about  twenty  calories, 
about  equal  to  the  heat-value  of  a  tumbler  of  milk. 


MILK. 

Like  eggs,  milk  contains  all  the  elements  necessary  for  the  main- 
tenance of  life,  and  hence  it  is  regarded  as  a  type  of  alimentary  sub- 
stances and  classed  as  a  perfect  food.  It  serves  very  well  as  an 
infant-food. 

The  quantitative  composition  of  cow's  milk  and  human  milk  is 
as  follows,  according  to  Bunge: — 

Carbo- 
Proteid.      Fat.  Hydrate.    Salt. 

Cows'  milk   3.5         3.7         4.9         0.7 

Human  milk    1.7         3.4         6.2         0.23 


Fig.  G. — Specimens  of  Milk,  viewed  tliroiigh  the  Microscope.      (Landois.) 
M,  Milk.     C,  Colostrum. 

The  amount  of  fat  and  cai-l)oliydrate  is  nearly  the  same  in  both. 
there  being,  however,  twice  as  much  proteid  and  nearly  three  times 
as  much  salt  in  cows'  milk  as  in  human  milk.  To  bring  cows'  milk 
to  the  same  condition  as  human  milk,  it  is  necessary  to  dilute  with  an 
equal  amount  of  water,  and,  at  the  same  time,  to  add  some  cream  and 
sugar. 

Milk  is  a  watery  solution  of  various  proteids,  a  carbohydrate  and 
salt,  containing  in  suspension  emulsified  fat.  Cows'  milk  is  an 
opalescent  solution,  with  a  characteristic  taste  and  an  amphoteric 
reaction.  The  specific  gravity  varies  between  1028  and  1034.  Micro- 
scopically, it  consists,  like  blood,  of  plasma  and  corpuscles,  or  glob- 
ules, of  fat.     Boiling  does  not  coagulate  fresh  milk,  but  forms  a  skin 


CHEMICAL  CONSTITUENTS  OF  BODY  AND  FOOD.  41 

on  its  surface,  which  is  chiefly  composed  of  caseinogen  innieshing  some 
fat-particles.  This  film  is  formed  by  the  drying  of  proteid  at  the 
siarface  of  the  milk.  The  chief  proteid  of  milk  is  a  phospho-proteid 
called  caseinogen,  which  can  be  precipitated  by  adding  to  the  diluted 
milk  a  weak  acid  or  by  saturating  it  with  a  neutral  salt.  The  chief 
peculiarity  of  caseinogen  is  its  coagulating  power  when  treated  with 
a  ferment,  rennin,  in  the  .presence  of  lime  salts.  The  coagiilation  of 
milk  depends  upon  the  change  of  a  soluble  proteid,  caseinogen,  into 
an  insoluble  body,  casein,  by  means  of  the  enzyme,  rennin,  and  the 
presence  of  lime  salts  is  necessary.  It  is  probable  that  the  rennin 
first  splits  the  caseinogen  into  two  bodies,  the  more  important  being 
soluble  casein,  which  then  combines  with  the  calcium  salts  to  form  a 
caseinate  of  calcium,  while  the  other  passes  into  solution  in  the  whey 
as  whey  proteid,  or  lacfoserum  proteose. 

The  casein  thus  generated  inmeshes  the  fat-granules  and  forms 
milk-curd.  This  curd,  like  the  blood-clot,  shrinks  after  a  few  hours 
and  an  opalescent  fluid,  or  serum,  called  whey,  is  expressed. 

This  whey  contains,  besides  the  whey-proteid,  or  lactoserum  pro- 
teose, traces  of  other  proteids  and  also  lactose  and  milk  salts.  The 
casein  of  cows'  milk  forms  large  masses  on  coagulation,  while 
women's  milk  forms  very  fine  flakes. 

The  lactose,  or  sugar  of  milk,  does  not  readily  ferment  with 
yeast,  but  it  is  capable  of  undergoing  a  special  fermentation,  by  which 
it  is  changed  by  the  lactic  acid  bacillus  into  lactic  acid,  and  this 
lactic  acid  is  further  split  up  into  butyric  acid.  These  two  acids, 
lactic  and  butyric,  precipitate  the  caseinogen  and  produce  the  curd  in 
sour  milk;  but  this  curd  is  quite  a  different  body  from  that  pro- 
duced by  rennin,  for  it  can  be  dissolved  by  a  weak  alkali,  and  then  the 
rennin  will  clot  it.  Potassium  oxalate,  which  precipitates  the  cal- 
cium in  the  milk,  prevents  the  clotting  of  the  milk.  The  other  pro- 
teids in  milk,  besides  caseinogen,  are  lactalbumin  and  lactoglobulin. 

Kumiss  is  mare's  milk  fermented.  It  contains  10  per  cent,  of 
solids.  3  per  cent,  of  alcohol,  2  per  cent,  of  fat,  2  per  cent,  of  sugar, 
1  per  cent,  of  lactic  acid.  1  to  2  per  cent,  of  casein,  and  1  volume 
per  cent,  of  carbonic  acid. 

Kephir  is  cows'  milk  fermented  by  kephir  grains. 

Matzoon  is  prepared  by  adding  to  milk  a  ferment  consisting  of 
some  form  of  yeast  and  the  lactic  acid  bacilli.  It.  however,  contains 
very  much  less  alcohol  and  carbonic  acid  than  kumiss.  Plasmon 
is  prepared  by  precipitating  casein  from  fresh  milk.  Then  it  is  dis- 
solved in  sodium  bicarl)onate  in  the  presence  of  free  carbon  dioxide, 


42  PHYSIOLOGY. 

which  prevents  the  alkali  from  decoiiiposing  the  casein.  It  is  then 
dried,  and  is  a  yeiiovvish-white  body.  It  contains  2  per  cent,  of  fat 
and  milk-sugar  and  7  per  cent,  of  salts.  It  is  used  as  a  substitute  for 
milk  when  a  large  amount  of  water  is  not  desirable. 

The  fats  of  milk  are  olein,  palmitin,  stearin,  caproin,  and  buty- 
rin.  The  milk  of  women  contains  twice  as  much  olein  as  palmitin 
and  stearin,  but  these  bodies  are  about  the  same  in  quantity  in  cows' 
milk.  In  cowls'  milk  two-fifths  is  olein,  one-third  is  palmitin,  one- 
sixth  stearin  and  butyrin,  and  caproin  one-fourteenth  of  the  total 
fat. 

Buttermilk  contains  about  10  per  cent,  of  solids,  including 
casein;     lactose;     and  about  1  per  cent,  of  fats. 

Butter  is  formed  in  churning  by  making  the  fat-particles  adhere 
to  each  other,  forming  a  yellow,  fatty  mass. 

The  salts  of  milk  average  0.6  per  cent,  and  they  consist  chiefly 
of  phosphate  of  lime  with  calcium  chloride,  magnesium  phosphate, 
and  traces  of  iron. 

Milk  also  contains  about  7.G  per  cent,  of  carbonic  acid  and  traces 
of  oxygen  and  nitrogen. 

The  quantity  of  milk  daily  secreted  by  a  woman  is  about  one 
quart. 

The  quantity  of  milk  changes  during  lactation,  wdiich  lasts  in  the 
woman  about  ten  months.  In  the  case  of  the  woman,  the  percentage 
of  casein  and  fat  increases  to  the  end  of  the  second  month,  but  sugar 
lessens  even  in  the  first  month.  During  the  fifth  to  the  seventh 
month  there  is  a  diminution  of  fat,  and  between  the  ninth  and  tenth 
months  a  decrease  of  casein.  In  the  first  five  months  the  salts 
increase;  after  that  they  diminish. 

Colostrum  is  the  milk  secreted  for  a  few  days  after  parturition, 
and  it  has  peculiar  characteristics.  It  contains  large  corpuscles  called 
colostrum-corpuscles,  which  are  large  cells  full  of  colorless,  fatty  par- 
ticles. 

A  poisonous  principle  is  sometimes  generated  in  milk  by  microbes. 
It  is  called  tyrotoxicon. 

VEGETABLE    FOODS. 

Vegetable  substances  differ  very  much  from  animal  bodies  in  their 
physical  appearances,  and,  in  some  respects,  also  chemically.  The 
vegetable  matters  are  capable  of  being  transformed  into  the  various 
animal  components  and  thereby  nourish  the  animal  body,  since  they 
contain  all  the  elements,  or  proximate  principles,  that  are  necessary 


CHEMICAL  CONSTITUENTS  OF  BODY  AND  FOOD.  43 

for  the  maintenance  of  life.  They  need  a  more  complex  apparatus 
for  their  transformation,  and,  as  a  consequence,  the  digestive  organs 
of  the  herbivora  are  better  developed  and  more  complex  than  those 
of  the  carnivora. 

The  cereals  have  the  same  general  composition,  all  containing 
the  same  proximate  principles,  but  not  all  possess  the  same  relative 
amounts,  because  of  which  some  are  more  valuable  as  food  than 
others.     The  most  important  of  the  cereals  is  wheat. 

^Vlleat,  as  a  source  of  food,  occupies  a  very  important  place  and 
is  one  of  the  most  widely  cultivated  of  the  cereals.  The  wheat- 
grains  by  grinding  have  their  cellulose  coats  burst,  and  the  resulting 
powder  is  called  flour.  This  contains,  on  an  average.  70  per  cent,  of 
'carbohydrates,  8  per  cent,  of  proteid,  and  1  per  cent,  of  fat.  The 
coverings  of  the  grain  still  contain  some  albumin  and  starch  and 
thus  form  l:)ran,  a  substance  used  for  feeding  the  herbivora.  Bread  is 
made  by  a  mixture  of  wheat-flour  and  water,  forming  dough.  The 
body  which,  on  the  addition  of  water,  becomes  viscid  is  called  gluten, 
and  is  a  tough,  sticky  mass.  This  is  made  more  porous  by  carbonic 
acid,  which  is  generated  in  the  dough  by  the  action  of  the  yeast-plant 
on  sugar.  The  sugar  is  produced  l^y  the  diastase  in  the  flour,  which 
hydrates  the  starch  into  sugar.  Baking  kills  the  yeast-action  and 
makes  the  vesicles  filled  with  carbonic  acid  expand,  so  the  dough  is 
filled  with  little  cavities.  The  crust  of  bread  is  formed  by  the  heat 
coagulating  the  gluten,  and  at  the  same  time  the  heat  transforms  the 
starch  into  dextrin  and  soluble  starch.  The  glazing  of  the  crust  is 
due  to  dextrin.  The  color  of  the  crust  and  its  taste  are  due  to  a 
caramel  generated  by  the  action  of  heat  on  the  sugar  produced  by  the 
diastase. 

ACCESSORY  FOODS. 

In  addition  to  the  ordinary  foods  there  is  a  series  of  articles 
which  are  not  necessary  to  the  maintenance  of  life,  but  which  are  fre- 
quently used.  They  are :  alcohol,  tea,  coffee,  and  cocoa.  Of  these 
accessory  foods,  alcohol  is  the  predominant  one  and  is  used  in  a  vari- 
ety of  drinks. 

Alcohol. — Beer  contains  from  3  to  5  per  cent,  of  alcohol.  It 
also  has  from  5  to  7  per  cent,  of  extractives,  which  consist  mainly  of 
dextrin  and  maltose,  with  all)uniinope.  which  give  it  nutrient  proper- 
ties. Each  ounce  usually  holds  about  two  cubic  inches  of  carbon 
dioxide.  It  is  an  infusion  of  malt  fermented,  to  which  a  bitter  prin- 
ciple foimd  in  hops  is  added.     It  is  frequently  adulterated  with  sali- 


44  PHYSIOLOGY. 

cylic  acid  and  benzoic  acid  to  preserve  it.  In  excess  it  gives  rise 
to  rheumatism,  gout,  and  bilious  attacks,  due  to  diminished  excretion 
of  waste-materials  from  the  economy.  Wines  contain  from  G  to  25 
per  cent,  of  alcohol.  Port  holds  10  per  cent,  and  sherry  IG  to  25  per 
cent,  of  alcohol.  Besides,  the  aroma  is  due  to  ethers.  Champagnes 
contain  in  addition,  10  per  cent,  of  sugar,  which  upsets  the  stomach. 
Wines  also  have  free  acids,  especially  tartaric,  which  also  disagree 
with  certain  stomachs. 

Spirits  contain  about  50  per  cent,  of  alcohol.  Alcohol  is  a 
nutrient  and  heat-generator.  One  gram  of  alcohol  produces  more 
heat  than  one  gram  of  proteid  or  carbohydrate.  Ordinarily  the  sys- 
tem can  oxidize  dail}^  about  one  and  one-half  ounces  of  alcohol.  When 
alcohol  is  oxidized  it  spares  the  fats  and  carbohydrates  and  probably 
the  proteids.  It  is  w^ell  known  that  the  continuous  drinking  of 
alcohol  makes  a  person  fat.  The  persistent  use  of  alcohol  also 
increases  the  dangers  of  infection  from  infectious  diseases.  In  fevers 
its  use  prevents  the  loss  of  fat  and  stimulates  the  secretion  of  gastric 
juice.  It  dilates  the  capillaries  of  the  skin  either  by  a  local  or  central 
action,  favoring  heat-dissipation.  Its  habitual  use  gives  rise  to 
chronic  gastritis  and  cirrhosis  of  the  liver.  The  odor  of  spirits  in 
the  breath  is  due  to  fusel-oil.  Alcohol  in  the  blood  is  changed  into 
carbonic  acid  and  water. 

Coffee. — Each  cup  of  coffee  contains  about  two  grains  of  caffeine. 
Coffee  also  contains  a  volatile  substance  called  coffeon,  which  resem- 
bles an  oil.  The  exhilaration  after  the  drinking  of  coffee  and  the 
increased  peristalsis  are  due  to  the  coffeon. 

Tea. — Tea  contains  caffeine  and  th(>ophyllino  and  about  7  per 
cent,  of  tannin.  Tea  induces  constipation  and  chronic  gastritis  .when 
used  in  excess.     Neither  tea  nor  coffee  diminishes  metabolic  changes. 

Cocoa. — This  body  is  a  nutrient  because  it  contains  fat  (50 
per  cent.)  and  an  all)uminous  substance.  It  contains  theobromine. 
Caffeine  and  theobromine  belong  to  the  purin  group. 


CHAPTER  111. 

DIGESTION. 

Anatomy  and  Structure  of  the  Mouth,  Pharynx,  and  (Esophagus, 
together   with    the    Digestive   Processes   Occurring   in    Them. 

Digestion  has  for  its  aim  the  separating  of  the  principles  of 
growth  and  repair  from  the  aliments  and  the  fitting  of  them  for 
absorption  into  the  circulation.  The  process  is  both  mechanical  and 
chemical,  accomplished  mainly  through  the  action  of  certain  soluble 
ferments  called  digestive  enzymes. 

Some  form  of  digestion  is  found  to  take  place  in  all  animal  organ- 
isms no  matter  how  low  we  proceed  in  the  zoological  scale.  It  is 
essential  to  every  one  of  them  that  they  be  able  to  take  from  their 
environments  those  elements  that  are  necessary  to  maintain  their 
economy  and  to  give  off  those  substances  termed  waste-products  that 
are  no  longer  fit  for  use.  for  only  by  this  exchange  of  the  elements 
outside  of  their  own  organisms  are  they  able  to  live,  grow,  and  pro- 
duce others  of  their  kind. 

In  the  higher  grades  of  animal  life,  as  the  articulata  and  verte- 
brata,  the  number  of  organs  concerned  in  digestion  is  increased,  and, 
of  course,  in  direct  ratio  the  various  stages  and  acts  in  the  whole 
process  are  multiplied.  In  their  bodies  it  is  a  long  tube,  in  some  parts 
much  folded  on  itself ;  in  and  along  the  outside  of  this  tube  there  are 
numerous  glands  which  empty  their  products,  called  secretions,  into 
the  long  tube;  at  the' beginning  of  which  there  is  an  apparatus  for 
crushing  and  grinding  the  solid  parts  of  the  food.  Intimately  con- 
nected with  this  apparatus  is  the  system  of  blood-  and  chyle-  vessels 
for  absorbing  the  digested  products,  thus  allowing  them  to  circulate 
through  the  entire  l^ody  and  come  into  contact  with  every  part  of  the 
organism. 

In  the  vertebrata  there  are  modifications  and  forms  of  develop- 
ment dependent  upon  the  class,  and  even  in  mammalia  there  are 
differences,  as  the  animal  may  be  insectivorous,  carnivorous,  herbivor- 
ous, or  omnivorous. 

Man,  the  highest  of  the  mammalia,  is  the  real  and  intimate  study 
upon  which  all  our  phvsiological  researches  bear.     He  is  omnivorous, 

(45) 


46  PHYSIOLOGY. 

and  naturally  wc  expect  to  lind  liis  digestive  apparatus  suited  to  dis- 
integrating and  dissolving  all  kinds  of  food. 

In  him  the  digestive  apparatus  consists  of  a  long  tube,  called  the 
alimentary  canal,  about  thirty  feet  in  length,  with  its  accessories,  the 
teeth  and  the  various  glands  which  empty  their  products  into  the  tube 
by  means  of  little  ducts. 

The  alimentary  canal  is  the  long  tube  beginning  with  the  mouth 
and  ending  with  the  anus,  composed  of  muscle  and  mucous  membrane, 
the  latter  lining  it  throughout  its  entire  length  and  giving  to  the 
interior  of  the  canal  its  characteristic  smoothness  and  redness.  In 
this  lining  membrane,  as  also  in  the  submucosa,  are  located  some  of 
the  glands  whose  secretions  aid  digestion. 

The  alimentary  canal  in  its  extent  of  about  thirty  feet  has 
received  various  names  for  its  several  parts.  They  are :  mouih, 
pharynx,  o'sophagus,  stomach,  small  and  large  intestines. 

The  mouth  is  an  oval  box  situated  at  the  commencement  of  the 
canal,  in  which,  by  the  action  of  the  jaws  with  their  two  rows  of  teeth, 
the  hard  parts  of  the  food  are  masticated.  While  the  food  is  being 
masticated,  it  is  at  the  same  time  being  mixed  with  a  watery  fluid, 
the  saliva,  the  secretion  of  the  salivary  glands;  this  mixing  of  food 
and  saliva  has  been  termed  insalivation. 

In  the  pharynx  and  oesophagus  occurs  the  act  of  deglutition,  or 
swallowing  of  the  masticated  mouthful,  in  the  form  of  a  large,  moist 
bolus.  It  is  by  the  contraction  of  the  muscles  in  these  parts,  that  the 
food  is  quickly  passed  on  to  the  stomach.  The  course  of  the  tube, 
beginning  with  the  mouth  and  ending  at  the  opening  of  the  stomach, 
is  comparatively  straight,  and  measures  about  fifteen  or  eighteen 
inches  in  length.  This  part  of  the  tube  is  found  in  the  head,  neck, 
and  thorax,  ending  just  below  the  transverse  muscular  wall  of  the 
trunk,  the  diaphragm. 

The  stomach  is  the  muscular  pouch  in  which  occur  some  of  the 
chemical  changes  of  the  food,  converting  it  into  a  grayish-brown  soup- 
like mass.  From  thence  it  passes  into  the  small  intestine,  where  the 
nutrient  materials  are  separated  from  the  waste-residue;  the  latter 
is  passed  on  into  the  large  intestine  to  be  later  expelled  from  the  body. 

The  stomach  and  the  large  and  small  intestines  are  located  in  the 
abdomen  and  pelvis,  differing  from  that  part  of  the  canal  above  the 
diaphragm  in  that  the  intestines  are  much  folded  and  convoluted  in 
their  course ;  so  that  the  major  portion  of  the  entire  length  of  the 
canal  is  contained  here. 

In   the   mucous   membrane   and    submucosa    are    located   micro- 


DIGESTION.  47 

scopical  glands  whose  ducts  open  directly  upon  the  lining,  interior 
surface.  Outside  the  canal,  their  secretions  emptying  into  the  canal 
by  small  ducts,  are  the  larger  glands,  salivary,  liver,  and  pancreas. 
The  ducts  of  the  salivary  glands  open  into  the  mouth ;  the  common 
duct  of  the  liver  and  pancreas  opens  into  the  first  fold  of  the  small 
intestine,  the  duodenum. 

Although  digestion  in  its  entirety,  as  it  occurs  in  the  alimentary 
canal,  is  in  its  nature  very  complex,  yet  there  are  three  natural  divi- 
sions of  the  whole  process  based  upon  the  changes  as  they  occur  (1) 
in  the  mouth  (including  the  pharynx  and  oesophagus),  (2)  in  the 
stomach,  and  (3)  in  the  intestines. 

It  is  the  intention  to  consider  the  changes  and  alterations  of  the 
foodstuffs,  whether  mechanical  or  chemical,  in  each,  together  with 
the  anatomy  of  the  parts  of  each  division  and  the  structure  of  the 
accessory  glands,  with  their  secretions  and  the  functions  they  bear  to 
the  completion  of  the  entire  work.  However,  the  fact  must  not  be 
lost  sight  of  that  these  divisions  are  only  arbitrary  and  for  conve- 
nience, as  no  real  line  can  be  drawn  at  the  various  stages,  since  all 
parts,  structures,  and  functions  work  in  harmony,  on  the  plan  of 
division  of  labor :  having  in  mind  one  common  end — the  dissolving 
of  the  food  so  that  it  can  become  a  part  of  the  circulation. 

PREHENSION. 

Before  the  processes  of  digestion  can  begin,  it  is  essential  that 
the  food  should  be  brought  to  and  placed  in  the  mouth,  the  beginning 
of  the  alimentary  canal,  for  only  in  some  of  the  infusoria  does  diges- 
tion of  the  food  take  place  outside  the  organism,  due  to  the  influence 
of  ferments  secreted  by  the  organism  to  be  nourished.  The  act  of 
bringing  the  food  to  the  mouth  has  been  termed  prehension. 

Nature  has  admirable  contrivances  for  this  act  wherever  we  look 
among  the  lower  animals.  The  monkey,  squirrel,  rat,  etc..  usually 
make  use  of  their  anterior  extremities  for  grasping  and  bringing  to 
their  mouths  the  food,  while  they  sit  upon  their  haunches.  The 
horse  makes  use  of  his  teeth  and  lips;  indeed,  his  upper  lip  is  very 
movable,  long,  and  endowed  with  extreme  sensibility.  It  is  his  means 
of  gathering  together  his  grain  and  bringing  it  to  the  incisors  which 
cut  it  up,  then  to  be  passed  along  by  tlie  tongue  to  the  molars  for 
grinding.  In  the  cow,  the  tongue,  in  the  cat  and  dog.  the  teetli  and 
jaws,  are  the  main  organs  of  prehension.  The  frog,  by  protruding 
his  long,  thin  tongue,  the  surface  of  which  is  covered  with  a  viscid 
mucus,  catches  insects   as  they  fly. 


48  PHYSIOLOGY. 

By  far  the  most  complicated  and  best  developed  prehensile  instru- 
ment in  animal  mechanics  is  that  employed  by  iiuin — the  human 
upper  limb.  The  extreme  perfection  of  all  its  parts,  and  particularly 
of  its  terminal  portion.,  the  hand,  makes  it  admirably  fitted,  not  only 
for  the  prehension  of  food,  but  also  for  the  execution  of  all  the  various 
caprices  and  designs  of  the  human  will.  Thus  it  not  only  simply 
raises  the  food  to  the  mouth  (prehension),  but  also,  with  the  human 
intelligence  as  the  real  potent  factor,  aids  in  the  preparation  of  food 
by  means  of  fire  (cooking). 

Thus  we  learn  that  the  first  real  step  in  digestion  is  prehension: 
bringing  the  food  to  the  mouth. 

THE  MOUTH. 

The  space  included  between  the  lips  in  front,  the  pharynx  behind, 
and  the  cheeks  at  the  side  is  the  mouth.  Above  the  roof  of  the  mouth 
we  have  the  palate;  below,  its  floor,  upon  which  rests  the  tongue. 
The  cavity  of  the  mouth,  excepting  the  teeth,  is  everywhere  invested 
with  a  highly  vascular  mucous  membrane,  with  an  investment  of 
squamous  epithelium.  Conical  papillae,  for  the  larger  part  minute 
and  concealed  beneath  the  epithelium,  are  found.  The  lips  are 
separated  by  the  oral  fissure.  They  are  composed  of  various  muscles 
converging  to  and  surrounding  the  oral  fissure.  The  cheeks  have  a 
composition  similar  to  the  lips,  and  their  principal  muscle  is  the  buc- 
cinator. At  their  back  part  they  include  the  ramus  of  the 
jaw  and  its  muscles,  and  usually  between  these  aud  the  buccinator 
muscle  is  a  mass  of  soft,  adipose  tissue. 

Beneath  the  mucous  memljrane  of  the  lips  and  cheeks,  there  are 
a  number  of  small,  racemose  glands,  with  ducts  which  open  into  the 
mouth.  These  glands  are,  in  the  lips,  called  labial  and.  in  the 
cheeks,  buccal.     They  secrete  mucus. 

There  are  two  parts  to  the  palate:  a  hard  and  a  soft  palate. 
The  hard  palate  is  deeply  vaulted  and  lined  with  a  smooth  mucous 
membrane,  except  at  its  anterior  part,  where  it  is  roughened  l)y  trans- 
verse ridges.  The  soft  palate  is  a  doubling  of  the  mucous  membrane, 
inclosing  a  fibromuscular  layer,  also  containing  racemose  glands.  It 
hangs  down  obliquely  from  the  hard  palate  between  the  mouth  and 
posterior  nasal  orifices.  It  is  a  freely  movable  partition.  The  uvula 
is  an  appendage  like  a  tongue  projecting  from  the  middle  of  the  soft 
palate,  and  consists  of  a  pair  of  muscles  inclosed  in  a  pouch  of  mucous 
membrane. 

Palate. — The  palate  has  two  crescentic  folds  of  mucous  mem- 


DIGESTION.  49 

brane  inclosing  muscular  fasciculi  and  diverging  from  the  base  of  the 
uvula,  on  each  side  of  the  palate  outward  and  downward,  one  to  the 
side  of  the  tongue,  the  other  to  the  side  of  the  pharynx.  These  folds 
are  known  as  the  half -arches  of  the  palate.  The  one  in  front  is  known 
as  the  anterior  palatine  arch,  the  one  posterior  as  the  posterior  pala- 
tine arch. 

The  Fauces. — The  fauces  is  the  strait,  or  passage,  leading  from 
the  mouth  to  the  pharynx,  and  corresponds  with  the  space  included 
between  the  half-arches  of  the  palate. 

The  Tongue. — The  tongue  is  composed  of  muscle  and  is  covered 
with  a  mucous  membrane.  It  is  composed  of  two  symmetrical  halves 
joined  in  the  middle  line.  By  the  freedom  of  its  movements  it  aids 
in  mastication  and  deglutition ;  it  is  also  a  great  help  in  articulation, 
and  by  the  papillas  on  its  surface  forms  an  organ  of  taste.  The 
root,  or  base,  is  the  posterior  part,  where  it  is  attached  to  the  hyoid 
bone  and  inferior  maxilla.  The  body  is  the  great  bulk  of  the  organ. 
Its  tip  is  the  anterior  free  extremity.  On  the  anterior  two-thirds  of 
the  upper  surface  of  the  tongue,  we  find  a  mucous  membrane,  which 
adheres  most  intimately  to  the  muscles  beneath.  Its  surface  is  rough- 
ened by  the  presence  of  a  number  of  little  papilla.  On  the  surface 
of  the  tongue  there  are  many  mucous  glands. 

Papillae. — The  papillse  are  the  fungiform,  filiform,  and  circum- 
vallate.  These  are  more  minutely  described  in  the  section  on  the 
sense  of  taste. 

Nerves. — The  nerves  of  the  tongue  are  the  lingual  of  the  fifth 
pair,  the  glosso-pharATigeal,  and  the  hypoglossal. 

THE  TEETH. 

In  form,  structure,  and  number,  the  teeth  vary  very  considerably 
in  different  animals :  this  is  markedly  shown  in  the  classes,  car- 
nivora  and  herbivora.  In  most  animals  the  teeth  are  worn  down 
by  use  and  eventually  decay.  The  exception  is  found  in  that  class 
of  animals  that  constantly  nibble ;  their  incisors  are  peculiar  in  that 
there  are  deposits  of  fresh  dentine  within  and  upon  the  pulp  and 
of  enamel  upon  the  anterior  surface,  thus  giving  a  continuous  growth. 
They  are  the  rodentia. 

Among  mammalia,  and  particularly  in  man,  the  teeth  are  devel- 
oped in  two  sets:  (1)  the  frst,  less  numerous  and  smaller  set.  called 
the  Umpomry.  or  mWk.  teeth;  (2)  the  second  set.  larger  and  more 
numerous,  called  the  permanent  teeth. 

The  temporary,  or  millc.  teetli  are  usually  20  in  number.  10  in 

4 


50  PHYSIOLOGY. 

each  jaw.  In  each  jaw  there  are  Jf.  incisors,  2  canines,  and  k  molars. 
When  the  milk  teeth  drop  out  they  are  followed  by  the  permanent 
teeth. 

The  permanent  teeth  are  32  in  number,  16  in  each  jaw,  consisting 
of  Jf.  incisors,  2  canines,  1^  bicuspids,  and  6  molars. 

There  are  three  distinct  parts  in  a  tooth :     crown,  root,  and  neck. 

The  crown,  or  body,  is  the  protruding  portion  of  the  tooth;  the 
portion  inserted  in  the  alveolus  of  the  jaws  is  the  root,  or  fang.  The 
slightly  constricted  part  enveloped  by  the  gum,  is  the  neck.  The  fang 
is  firmly  fastened  to  the  sides  of  the  alveolus,  in  which  it  is  inserted 
by  fibrous  tissue,  which  is  continuous  with  the  periosteum  of  the  jaws. 
When  the  jaws  are  closed  the  under  incisors  are  inclosed  by  the  upper 
ones.  Init  the  grinding  surfaces  of  the  molars  are  in  contact. 

Temporary  Teeth. — There  are  20  milk  teeth,  10  in  each  jaw,  or 
5  on  each  side  of  the  jaw;  that  is,  2  incisors,  1  canine,  and  2  molars. 
The  temporary  set  resembles  the  permanent  in  form  and  structure. 
The  teeth  are,  however,  fewer  in  number,  smaller  in  size,  and  charac- 
terized by  the  bulging  out  of  the  crown  close  to  the  neck,  making  the 
latter  very  sharply  defined.  Lower  central  incisors  are  the  first  to 
appear.     They  appear  about  the  seventh  month. 

The  milk  teeth  die  off  and  so  give  room  for  the  second  and  more 
permanent  set.  They  die  partly  in  accordance  with  the  rule  of  epi- 
thelial tissues  and  drop  off,  since  all  such  tissues  are  expelled  after 
their  death ;  then,  too,  the  jaws  grow  as  the  being  passes  from  infancy 
to  adult  life,  when  larger  and  more  numerous  teeth  must  replace  the 
smaller  ones,  so  as  not  to  impair  the  efficiency  necessary  to  masticate 
quantities  of  food  proportionate  to  the  demands  of  the  growing  body. 

Permanent  Teeth. — They  are  32  in  number.  There  are  8  in- 
cisors and  they  form  the  4  front  teeth  in  each  jaw,  and  are  named 
incisors  because  they  divide  the  food.  The  upper  incisors  are  the 
larger.  The  lower  molar  is  the  first  to  appear  in  the  permanent 
set.     It  appears  about  the  sixth  year. 

The  canine  teeth  are  4  in  number,  larger  than  the  incisors.  The 
upper  canines  are  usually  called  the  eye  teeth,  and  they  are  longer 
and  larger  than  the  canine  teeth  in  the  lower  jaw.  In  the  carnivorous 
animals,  like  the  dog,  the  canine  teeth  are  usually  large;  hence  the 
name  of  canine.  The  lower  canines  are  popularly  known  by  the  name 
of  stomach  teeth.  There  are  4  premolars,  or  bicuspids,  in  each  jaw. 
They  are  shorter  and  smaller  than  the  canines.  The  bicuspids  of  the 
upper  jaw  are  larger  than  those  of  the  lower  jaw.  The  functions  of 
the  bicuspids  are  to  cut  and  grind  the  food.     The  molars  are  12  in 


DIGESTION. 


51 


Fig.  7. — Longitudinal  Section  of  a  Molar  Tooth  of  Man. 

( SOBOTTA. ) 


X  8. 


The  figure  gives  a  general  view  of  the  structure  of  the  tooth.  The  pulp 
cavity  is  not  cut  its  whole  length  in  the  two  roots  seen  in  the  section.  We 
recognize  the  three  main  elements  of  the  tooth— dentine,  enamel,  and  cemen- 
tum— and  their  division  into  crown  and  root.  On  account  of  the  low  magnifica- 
tion, the  interglobular  spaces  appear  only  as  a  dark  zone  on  the  surface  of  the 
dentine.     C,  Cementum.     D,  Dentine.     P,  Pulp  cavity.     8.  Enamel. 


52 


PHYSIOLOGY. 


number,  3  on  each  side  above  and  below.  Their  large  crown  and 
their  groat  width  are  the  chief  distinguishing  characteristics.  The 
u])per  molars  have  3  conical  fangs,  the  lower  ones  3.  Tlie  last  molar 
is  the  wisdom  tooth,  so  called  because  it  appears  about  the  twentieth 
year,  when  the  individual  is  assumed  to  have  acquired  wisdom.  The 
molars  are  intended  for  the  grinding  of  food. 

Structure  of  the  Teeth. — If  a  tooth  is  split  in  its  long  axis  the 
surface  exhibits,  besides  the  pulp-cavity,  th^-ee  different  kinds  of 
materials.     Dentine  forms  the  greater  part  of   the  yellowish-white 

So  Dk 


Fig.  8. — Portion  of  the  Crown  of  a  Longitudinal   Section  of  a  Human 
Premolar.      X  200.      (Sobotta.  ) 

The  figure  shows  the  structure  of  a  tooth  at  the  border  of  enamel  and  dentine. 
In  the  region  of  the  dentine  two  larger  and  two  smaller  interglobular  spaces 
are  shown.  The  dentinal  fibers  branch  and  fork  and  with  their  processes  pass 
beyond  the  limits  of  the  enamel.  In  the  figure,  the  enamel  prisms  show  partly 
wavy  curves  and  partly  alternating  stripes  of  darker  and  brighter  prisms  (the 
parallel  stripes  of  Retzius).  D,  Dentine.  Dk,  Dentinal  tubules.  J<J,  Inter- 
globular spaces.    8,  Enamel.    Sp,  Enamel  prisms. 

substance;  the  capping  of  the  crown  is  enamel;  and  the  translucent, 
thin  investment  on  the  fang  is  cement,  or  crusta  petrosa. 

The  inain  bulk  of  the  tooth  is  composed  of  dentine,  giving  it 
shape  and  containing  the  pulp-cavity.  It  consists  of  about  28  parts 
of  organic  matter  and  73  of  earthy  material.  Dentine  resembles  bone 
both  physically  and  in  chemical  constitution.  When  subjected  to 
microscopical  examination  we  find  the  dentine  penetrated  throughout 


DIGESTION. 


63 


by  fine  tubes  called  dentinal  tubules.  The  inner  ends  of  these  tubules 
open  into  the  pulp-cavity,  whence  they  radiate  in  every  part  of  the 
dentine  toward  the  surface  of  the  tooth.  They  have  a  direction  gen- 
erally parallel,  with  a  wavy,  undulating  course.  In  the  pathway 
toward  the  periphery  they  subdivide  into  several  parallel  branches 
which  anastomose  with  each  other.  The  average  diameter  of  the 
tubule  is  ^Aeoo  inch.  Near  the  end  of  the  tubule  the  arrangement  is 
in  globular  spaces  which  communicate  with  each  other  and  are  known 
as  the  interglobular  spaces  of  Purkinje,  or  Tomes  granular  sheath. 


Fig.   9. — Portion 


of  a   Longitudinal    Section   of   the   Root   of   a 
Molar  Tooth.      X  200.      (  Sobotta.  ) 


Human 


The  figure  shows  the  structure  of  the  boundary  between  dentine  and  cemen- 
tum.  In  the  cementum  distinct  bone  spaces  with  bone  canaliculi  are  seen. 
The  dentinal  tubules  here  show  especially  numerous  divisions  and  lateral 
branches.  The  granular  layer  shows  small,  irregular  interglobular  spaces.  C. 
Cementum.  D,  Dentine.  Dk,  Dentinal  tubules.  K,  Granular  layer  (small 
interglobular    spaces).       KH,    Bone   spaces    of   the    cementum. 

Enamel. — The  hardest  of  all  organized  substances  is  known  as 
enamel.  It  is  a  bluish-white  material  capping  the  crown  of  the  tooth. 
It  is  thickest  on  the  triturating  surface  of  the  tooth.  Chemically  it 
consists  of  3  parts  of  organic  matter  and  97  of  earthy  matters,  prin- 
cipally calcium  phosphate.  Under  the  microscope  the  enamel  appears 
in  the  form  of  hexagonal  columns  about  ^/sooo  i^^ch  in  diameter. 

The  Cement,  or  Crusta  Petrosa. — This  substance  covers  the 
fang  of  the  tooth,  gradually  becoming  thicker  toward  its  extremity. 


54 


PHYSIOLOGY. 


It  is  like  true  bone,  and  contains  lacunae  and  canaliculi.  Externally 
it  is  covered  by  dental  periosteum.  In  old  age  the  cement  grows 
thicker  and  may  close  up  the  entrance  to  the  pulp-cavity. 

THE  SALIVARY  GLANDS. 

The  parotid  gland  is  named  from  its  position  near  the  ear.  It 
is  the  largest  of  the  salivary  glands.  It  extends  upward  as  far  as  the 
zygoma,  downward  as  far  as  the  angle  of  the  lower  jaw,  and  inward 
between  the  ramus  of  the  jaw  and  the  mastoid  process.  The  duct  of 
the  parotid,  called  Stenos,  has  the  diameter  of  a  crow-quill,  is  two 
inches  in  length,  and  runs  across  the  masseter  to  open  into  the  mouth 
opposite  the  second  molar  tooth 


Fig.    10. — Histology  of  the   Salivary  Glands.      (Landois.) 

B,  Alveoii  of  the  rested  submaxiUary  of  the  dog.  c.  The  distended,  glistening 
mucous  cells,  d,  Gianuzzi's  crescents.  C,  The  alveoli  after  active  secretion, 
showing    the   connective    tissue    of    the    alveoli    isolated   at   D. 

The  parotid  has  a  full  supply  of  blood-vessels,  which  run  through 
it.  The  nerves  of  the  parotid  are  the  auriculo-temporal  and  the 
cervical  sympathetic.  In  the  dog  and  cat  the  parotid  derives  its 
nerve-supply  from  the  glosso-pharyngeal  through  the  small  petrosal 
and  the  otic  ganglion,  the  fibers  finally  running  into  a  branch  of  the 
auriculo-temporal. 

The  submaxillary  gland  is  separated  from  the  parotid  by  a  pro- 
cess of  the  deep  cervical  fascia.  It  is  beneath  the  mylohyoid  muscle, 
is  below  the  curve  of  the  digastric  muscle,  and  on  the  outside  is 
covered  by  the  subcutaneous  cervical  muscle  and  skin.  It  is  about  one- 
third  the  size  of  the  parotid,  and  its  duct  of  Wharton  is  about  two 


DIGESTION.  55 

inches  in  length.  The  duct  opens  on  the  side  of  the  lingual  fraenum. 
The  blood-vessels  are  branches  of  the  facial  and  lingual.  The  nerves 
are  those  from  the  submaxillary  ganglion,  and  through  this,  from  the 
chorda  tympani.     The  sympathetic  also  supplies  this  gland. 

The  sublingual  gland  rests  on  the  floor  of  the  mouth  and  is  seen 
beneath  the  side  of  the  tongue  as  a  ridge.  It  has  a  half-dozen  ducts 
called  the  Eivinian.  which  open  on  the  ridge  that  marks  the  position 
of  the  gland  on  the  side  of  the  fraenum. 

STRUCTURE  OF  THE  SALIVARY  GLANDS. 

These  glands  are  of  the  compound  racemose  variety.  The  alveo- 
lus has  a  duct  ending  in  it.  The  alveoli  are  united  by  the  blood- 
vessels and  a  small  amount  of  loose  connective  tissue  with  lobules. 
The  alveoli  of  the  salivary  glands  are  divided  into  two  classes,  accord- 
ing to  the  kind  of  secretion,  one  kind  giving  a  secretion  containing 
mucin,  and  the  other  kind  secreting  a  more  watery  fluid  containing  a 
large  amount  of  serum-albumin ;  hence  the  alveoli  are  mucous  or 
serous.  The  sublingual  chiefly  secretes  mucus,  the  parotid  chiefly 
serum-albumin.  The  submaxillary  secretes  both  kinds.  In  most  of 
the  alveoli  of  the  glands,  there  are  found  cells  of  a  kind  differing  from 
the  mucin-cells,  as  in  the  submaxillary  of  the  cat,  where  they  form 
an  almost  complete  outer  layer,  next  to  the  base  membrane  and  inclos- 
ing the  mucin-cells,  and  are  called  "marginal  cells."  In  the  dog's 
submaxillary  they  are  seen  only  as  semilunar  masses  known  as  the 
half-moons  of  Gianuzzi.  The  lymphatics  lie  closer  to  the  alveoli  than 
the  capillary  network  of  blood-vessels.  The  lymphatics  begin  in  the 
form  of  lacunae,  between  and  around  the  alveoli.  The  nerves  pierce 
the  basement  membrane  and  arborize  between  and  around  the  cells 
of  the  alveoli. 

PHARYNX. 

The  phar^mx  is  a  funnel-like  cavity  running  from  the  under  sur- 
face of  the  skull  down  to  the  level  of  the  fifth  cervical  vertebra,  where 
it  ends  in  the  oesophagus.  There  are  7  openings  communicating  with 
it:  the  2  posterior  nares.  the  2  Eustachian  tubes,  the  mouth,  the 
larynx,  and  the  oesophagus.  The  walls  of  the  pharynx  are  musculo- 
membranous.  The  interior  is  lined  with  a  soft,  red,  mucous  mem- 
brane containing  many  glands.  Squamous  cells  are  the  chief  variety 
of  epithelium  lining  the  mucous  membrane.  Xext  is  a  fibrous  coat, 
then  a  muscular  coat,  and  outside  of  this  a  fibrous  investment  which 
attaches  it  to  the  skull.     The  muscular  coat  includes  the  superior. 


56  PHYSIOLOGY. 

middle,  and  inferior  constrictors  of  the  pharynx,  which  are  concerned 
in  deglutition.  Lymphoid  tissue  is  very  abundant  at  the  upper  back 
part  of  the  pharynx,  and  a  number  of  lympli-follicles  lie  between  the 
orifices  of  the  Eustachian  tubes,  forming  the  pharyngeal  tonsil. 

(ESOPHAGUS. 

This  tube  extends  from  the  fifth  cervical  down  to  the  ninth  dorsal 
vertebra.  It  is  about  nine  inches  long  and  less  than  an  inch  in 
diameter.  It  is  narrowest  at  its  commencement  and  gradually  en- 
larges. It  has  three  coats :  the  outside,  muscular ;  a  middle  coat, 
fibrous;  and  an  internal,  or  mucous,  coat.  The  muscular  coat  has 
a  layer  of  longitudinal  fibers  and  a  layer  of  circular  fibers ;  the  upper 
end  of  the  oesophagus  has  striated  fibers,  while  the  lower  half  has 
plain,  unstriped  fibers.  The  mucous  coat  is  paler  than  that  of  the 
pharynx  and  mouth.  In  ordinary  circumstances  the  mucous  mem- 
brane is  in  longitudinal  folds.  It  contains  minute  papillae  and  a 
squamous  epithelium.  The  nerves  of  the  oesophagus  are  the  vagus 
and  the  sympathetic. 

THE  MECHANICAL  PROCESSES  OF  DIGESTION  OCCURRING 
IN  THE  MOUTH,  PHARYNX,  AND  (ESOPHAGUS. 

MASTICATION. 

This  is  a  voluntary  act  whereby  the  food  is  comminuted  by  the 
teeth,  jaws,  and  muscles  concerned  in  this  act,  aided  by  the  tongue, 
palate,  cheeks,  and  lips.  The  bulk  of  the  work  is  accomplished  by 
the  biting  and  grinding  movements  of  the  lower  teeth  against  the 
upper  ones. 

From  the  manner  of  its  articulation  with  the  skull  the  lower  jaw 
is  capable  of  performing  three  primary  movements,  together  with 
combinations  of  these  same,  viz. :  up  and  down,  side  to  side,  with 
projection  and  retraction.  The  muscles  concerned  in  producing  these 
movements  are  the  masseter,  temporal,  and  internal  pterygoids,  which 
raise  the  lower  jaw;  the  inferior  maxillary  division  of  the  fifth  nerve 
innervates  them.  The  depression  of  the  jaw  is  accomplished  mainly 
through  the  action  of  the  digastric,  aided  considerably  by  gravity. 
The  side-to-side,  or  lateral,  movements  are  due  to  the  separate  action 
of  the  external  pterygoids.  Their  united  contraction  gives  projection 
of  the  lower  mandible,  to  be  retracted  by  a  part  of  the  temporal 
muscle.  The  innervation  of  the  pterygoids  is  also  by  the  inferior 
division  of  the  fifth. 


DIGESTION.  57 

Mastication  is  particularly  important  when  solid  and  fibrous  foods 
are  eaten,  to  prepare  them  by  comminution  for  the  fermentative 
action  of  the  various  digestive  fluids.  When  improperly  performed 
repeatedly,  a  severe  form  of  dyspepsia  ensues. 

During  mastication  there  is  performed  a  separate  and  distinct 
act,  insalivation,  or  the  mixing  of  the  food  with  saliva.  By  means  of 
it,  the  dry.  hard  portions  of  food  are  moistened  and  softened  the  better 
to  fit  them  for  swallowing;  at  the  same  time  the  mucous  membrane 
is  lubricated  to  allow  free  movement  of  the  food  over  its  surface,  and 
the  surfaces  of  the  teeth  are  freed  from  accumulations  of  food  dur- 
ing mastication,  which  otherwise  would  collect  and  impede  its  pro- 
gress. A  fever  patient  attempting  to  swallow  a  dry  cracker  afi^ords 
ample  illustration  of  the  mechanical  value  of  the  saliva  during  mas- 
tication. 

DEGLUTITION. 

The  swallowing  of  the  food,  which  has  been  named  the  act  of 
deglutition,  is  performed  by  the  aid  of  the  tongue,  fauces,  pharynx, 
and  the  oesophagus  or  gullet.  For  the  purpose  of  description  only, 
since  the  process  in  reality  admits  of  no  lines  of  distinction,  this  act 
is  usually  said  to  comprise  three  stages:  first,  that  in  which  the  food 
is  forced  backward  from  the  mouth,  through  the  fauces  into  the 
pharynx.  This  act  is  voluntary,  though  usually  performed  uncon- 
sciously, being  ascribed  to  the  movements  of  the  tongiie  itself.  The 
second  stage  is  that  in  which  the  bolus  is  made  to  travel  along  the 
middle  and  lower  part  of  the  pharynx  to  the  oesophagus.  This  sec- 
ond act  is  more  complicated  and  requires  quicker  movements,  because 
the  nasal  and  laryngeal  orifices  are  open,  but  past  which  the  food  must 
go  without  entering.  The  main  motive  power  for  this  performance 
is  gained  l^y  the  contractions  of  the  three  constrictors,  aided  by  the 
synchronous  action  of  other  muscles,  whose  duty  is  to  occlude  tem- 
porarily the  nasal  and  laryngeal  openings.  The  opening  into  the 
nasal  cavity  is  closed  by  the  elevation  of  the  soft  palate,  uvula,  and 
the  contraction  of  the  posterior  pillars  of  the  fauces.  Just  above  the 
larATigeal  opening  and  at  the  base  of  the  tongue  is  a  small,  leaf- 
shaped  piece  of  cartilage,  the  epiglottis.  It  was  formerly  believed  that 
the  laryngeal  orifice  was  guarded  during  deglutition  by  the  retraction 
of  the  tongue  pressing  down  the  epiglottis  to  fit  it  firmly.  But,  as 
removal  of  the  epiglottis  did  not  interfere  with  normal  swallowing,  it 
was  learned  that  the  real  safeguard  was  the  contraction  of  the  arijteno- 
epiglottic  folds.     The  third  stage  is  that  in  which  the  bolus  descends 


58  PIIYSIOLOOY. 

along  the  oesophagus  to  enter  the  stomach.  This  stage  is  performed 
by  the  intrinsic  contractions  of  the  muscular  fibers  of  the  oesophagus- 
walls.  As  is  known,  its  muscular  fibers  are  arranged  in  two  layers: 
one  circular,  the  other  longitudinal.  The  upper  third  is  composed  of 
striated  muscle-fibers,  the  lower  two-thirds  of  plain,  or  unstriped, ' 
variety.  Accordingly  in  the  upper  third  the  movement  of  the  bolus 
is  more  rapid  than  in  the  lower  two-thirds.  The  movement  through 
the  cesophagus  is  that  known  as  peristaltic^,  or  vermicular.  The  sec- 
ond and  third  stages  of  deglutition  are  involuntary.  When  the  death- 
rattle  occurs  it  is  caused  by  the  pharynx  not  contracting  around  the 
bolus. 

Swallowing  of  Fluids. 

From  what  has  been  said  previously  it  will  be  readily  perceived 
that  the  act  of  deglutition  of  both  liquids  and  solids  is  a  muscular 
act,  and  not.  therefore,  dependent  upon  gravity.  Thus,  horses  and 
many  other  animals  drink  with  their  heads  low,  so  that  the  fluid  must 
needs  be  forced  up  an  inclined  plane  to  reach  their  stomachs.  Some- 
times jugglers,  while  standing  upon  their  heads,  perform  the  feat  of 
drinking. 

The  deglutition  of  boli  or  food  was,  for  convenience,  divided 
into  three  stages,  but  so  quickly  is  the  passage  of  liquids  accomplished 
that  physiologists  are  able  to  recognize  but  one  movement.  We  are 
indebted  to  the  experiments  and  observations  of  Kronecker  and 
Meltzer  for  an  explanation  of  this  process;  according  to  them,  there 
is  an  action  resembling,  in  the  main,  that  of  a  force-pump,  whereby 
the  mass  of  liquid  is  propelled  with  extreme  rapidity  through  the 
pharynx  and  oesophagus. 

It  is  by  the  contraction  of  the  two  mylohyoids  that  the  liquid 
is  put  under  high  pressure  and  shot  along  in  the  direction  of  least 
resistance:  through  the  pharynx  and  oesophagus.  This  pair  of  mus- 
cles is  greatly  aided  by  the  simultaneous  action  of  the  two  hyoglossi 
muscles.  These  two  pairs  of  muscles,  by  acting  in  unison,  form  a 
sort  of  diaphragm  to  push  the  root  of  the  tongue  backward  and  down- 
ward, at  the  same  time  performing  a  force-pump  action  upon  the 
liquid  to  be  swallowed.  So  quickly  is  the  passage  of  the  liquid  accom- 
plished that  the  pharyngeal  and  oeso])hageal  muscles  have  not  time  to 
contract  about  the  mass  of  liquid ;  in  fact,  they  are  inhibited  during 
the  passage  of  liquids  through  their  respective  channels.  After  the 
liquids  arrive  in  the  stomach  the  act  of  deglutition  ensues  for  the  pur- 
pose of  removing  the  liquids  adhering  to  the  walls  of  oesophagus. 


DIGESTION.  59 

This  statement  is  substantiated  very  strikingly  in  cases  of  poison- 
ing by  carbolic  acid  and  other  corrosive  substances.  The  mouth  and 
tongue,  from  longer  contact,  are  always  burned,  while  the  pharynx 
and  oesophagus  may  escape  altogether,  or,  at  most,  are  but  slightly 
burned.  The  escape  of  the  latter  is  due  to  the  rapid  transit  of  the 
corrosive  substance  through  them.  However,  the  cardiac  entrance 
of  the  stomach  is  always  very  much  corroded  before  the  sphincter 
relaxes  for  admission  into  the  stomach. 

When  the  ingested  food  has  been  thoroughly  insalivated  or  is 
semisolid,  there  begins  to  be  a  departure  from  the  three-stage  act 
toward  the  force-pump  action  of  liquids.  When  the  food  is  very 
much  liquefied  the  latter  action  is  very  prominent;  so  that  any  fixed 
line  for  the  swallowing  of  food  or  liquids  does  not  exist. 

Nervous   Control    of    Deglutition. 

Deglutition  is  a  reflex  act.  Every  reflex  act  requires  an  afferent 
set  of  sensory  nerves,  a  reflex  center,  and  an  efferent  set  of  motor 
nerves,  that  of  swallowing  no  less  so  than  any  other.  The  sensory 
nerves  have  their  terminations  in  the  mucous  membrane  of  the 
pharynx  and  oesophagus,  including  branches  of  the  glosso-phavyngeal 
to  the  tongue  and  pharynx,  branches  of  the  fifth  to  the  soft  palate, 
and  the  superior  laryngeal  branch  of  the  vagus  innervating  the  glottis 
and  epiglottis.  The  reflex  center  lies  somewhere  forward  in  the 
medulla.  The  efferent  nerves  are:  branches  of  the  fiftli,  which  sup- 
ply the  digastric,  mylohyoid,  and  muscles  of  mastication;  the  facial, 
which  supplies  the  levator  palati ;  the  glosso- pharyngeal  supplies  the 
muscles  of  the  pharynx.  Stimulation  of  central  end  of  the  superior 
laryngeal  calls  out  an  act  of  deglutition.  Stimulation  of  central  end 
of  the  glosso-pharvngeal  arrests  it.  The  inferior  laryngeal  branch 
of  the  vagus  innervates  the  muscles  of  the  lar}Tix,  while  the  hypo- 
glossal is  distributed  to  the  intrinsic  muscles  of  the  tongue.  Division 
of  the  two  vagi  is  followed  by  paralysis  of  both  oesophagus  and 
stomach,  with  a  very  firm  contraction  of  the  circular  band  of  fibers 
guarding  the  cardiac  orifice.  Therefore  these  nerves  send  motor  fibers 
to  the  oesophagus  and  stomach,  but  inhibitory  ones  to  the  cardiac 
sphincter.  So  firm  is  the  tetanic  contraction  of  the  sphincter  that  if 
food  is  swallowed  after  division  of  the  vagi  it  accumulates  within  the 
oesophagus,  no  part  of  it  passing  into  the  stomach. 

The  act  of  swallowing  inhibits  the  vagus  center,  for  a  single  act 
of  deglutition  increases  the  pulse-rate.  This  influence  upon  the  heart- 
beat is  dependent  upon  neither  the  amount,  character,  nor  temperature 


60  PHYSIOLOGY. 

of  the  bolus  swallowed.  It  is  influenced  only  by  the  reflex  act  and 
the  summation  of  other  aets.  It  also  has  an  inhibitory  influence  upon 
the  respiration.  'J'liis  is  very  evident  during  rapid  drinking  in  an 
animal  with  a  tracheotomy  tube.  For  increasing  the  activity  of  the 
heart's  action  a  tablespoonful  of  water  taken  in  a  large  number  of 
swallows  is  more  beneficial  than  a  glass  of  wine  taken  in  one  swallow. 

THE  CHEMICAL  CHANGES  OCCURRING  IN  THE  MOUTH 
DURING  DIGESTION. 

As  before  stated,  the  chief  aim  of  digestion  in  the  animal  econ- 
omy is  the  reduction  of  the  alimentary  substances  into  a  soluble  and 
absorbable  condition,  so  they  can  pass  through  the  various  animal 
membranes  and  become  components  of  the  tissues  and  blood  of  the 
body.  Xo  matter  how  soft,  through  the  influence  of  insalivation,  or 
finely  divided  and  triturated  by  reason  of  mastication,  the  food  may 
be,  it  cannot  become  a  constituent  of  the  body  until  it  has  been  acted 
upon  chemically  and  dissolved  by  the  various  ferments  present  in  the 
different  digestive  fluids. 

When  food  enters  the  mouth,  the  commencement  of  the  digestive 
tract,  the  first  digestive  fluid  that  it  comes  in  contact  with  is  the 
saliva.  Besides  its  mechanical  functions  of  moistening  and  softening 
the  food  to  render  easier  the  task  of  swallowing  it  in  the  form  of  boli, 
it  performs  other  duties  of  a  chemical  nature. 

First,  by  reason  of  its  watery  base,  it  has  the  power  to  dissolve 
saline  substances,  the  organic  acids,  alcohols,  sugars,  and  a  few  other 
substances  soluble  in  water. 

Secondly,  it  has  the  power  to  transform  certain  materials,  as 
starches,  into  maltose,  a  form  of  sugar.  The  starch  must  have  its 
cellulose  coat  dissolved  by  boiling,  however,  for  the  ferment  in  saliva 
will  not  act  readily  upon  cellulose.  The  active,  transforming  prin- 
ciple in  saliva  is  an  unorganized  ferment,  or  enzyme,  to  which  the 
name  ptyaJin  has  been  given.  The  conversion  of  starch  into  dextrin 
find  maltose  by  it  is  known  as  the  nmylolytic  action  of  saliva.  Its 
action  is  by  mere  contact,  for  no  appreciable  change  in  quantity  or 
character  is  noted  in  it  after  its  functions  are  performed,  and  so  active 
is  it  that  it  is  able  to  convert  two  thousand  times  its  own  weight  of 
starch  into  dextrin  and  maltose. 

The  word  "ase"  is  given  to  an  enzyme,  and  this  is  preceded  by 
the  name,  or  its  root,  of  the  substance  upon  which  it  acts.  Thus, 
ptyalin,  an  amylase  (amylum,  starch),  breaks  up  starch  into  maltose. 
Thus,  saccharase  or  invertase  of  the  small  intestines  acts  on  saccha- 


DIGESTION.  61 

rose  and  produces  glucose  and  fructose,  which  can  be  absorbed  and 
-assimilated. 

The  bacillus  coli  communis,  a  normal  denizen  of  the  large  intes- 
tine, secretes  lactase,  which  breaks  up  lactose. 

Lipase  or  steapsin  breaks  up  fats  into  fatty  acid  and  glycerin. 

We  have  proteases  which  break  up  the  proteids  into  peptones, 
and  the  peptones  into  amino-acids.  The  proteases  are  pepsin,  trypsin, 
erepsin,  and  enterokinase. 

We  have  the  coagulases.  such  as  rennin  and  the  fibrin  ferment 
(thrombase). 

Certain  fungi  (Russula  and  Boletus),  when  cut,  have  a  blue  or 
black  color  on  their  surface,  due  to  a  melanin  formed  by  an  enzyme, 
tyrosinase,  acting  on  tyrosin.  Both  these  bodies  are  free  in  the  plant, 
hut  come  in  contact  when  the  tissues  are  injured.  Tyrosinase  exists 
in  animal  tissues.  Within  recent  times  it  has  been  found  that  malt- 
ase,  when  added  to  a  40  per  cent,  solution  of  glucose,  reverses  its 
action  and  builds  up  maltose  until  1-i  per  cent,  of  maltose  is  formed, 
when  it  stops.  This  resembles  a  chemical  action — constant  breaking 
down  of  maltose,  but  constant  building  up  at  the  same  rate.  Lipase 
has  a  similar  reversing  action,  but  it  has  not  been  found  true  for 
other  enzymes.  Hence  maltase  and  lipase  are  destructive  and  con- 
structive, and  may  be  agents  by  which  the  cell  maintains  its  nutri- 
tive balance  between  its  protoplasm  and  the  surrounding  extracellular 
lymph. 

The  hydrolytic  action  of  enzymes  upon  the  sugars  depends  upon 
their  stereo-isomeric  form.  From  glucose  and  methyl-alcohol  there 
results  Alpha-methyl-glucoside  and  Beta-methyl-glucoside.  If  the 
enzymes  of  yeast  are  tested  on  these  two  compounds,  which  differ  only 
in  stereo-chemical  relationship,  it  is  found  that  only  the  Alpha-modi- 
fication is  hydrolyzed.  The  Beta  one  is  quite  resistant.  Hence,  accord- 
ing to  Fischer's  statement,  the  ferment  and  its  substance  must  fit  like 
the  lock  and  key,  or  the  reaction  does  not  occur. 

The  action  of  ferments  is  to  quicken  a  process  of  hydrolysis 
which,  without  their  presence,  would  take  a  long  time  for  its  accom- 
plishment. 

Ferments  do  not  initiate  a  chemical  action,  Init  alter  the  velocity 
of  reaction,  which  occurs  in  their  absence,  only  then  much  more 
slowly  or  much  more  quickly. 

Saliva,  as  it  appears  in  the  mouth,  is  a  thick,  glairv,  generally 
frothy  and  turbid  fluid.  It  is  a  mixed  fluid,  its  secretions  being 
derived    from    the    parotid,    sulunaxillary,    and    sublingual    salivary 


62  PHYSIOLOGY. 

glands,  and  contains  mucin  procured  from  the  labial,  lingual,  and 
buccal  glands.  Then,  too,  it  contains  some  debris  of  food,  bacteria, 
and  the  so-called  salivary  corpuscles.  Its  thick,  ropy  nature  is  due 
to  the  presence  of  the  mucin  in  it.  Normal  saliva  is  alkaline  in 
reaction,  but  in  some  forms  of  dyspepsia  it  becomes  somewhat  acid. 
The  specific  gravity  ranges  from  1.002  to  1.006. 

The  amylolytic  action  of  saliva  is  sensitive  to  changes  of  tem- 
perature, a  low  temperature  either  retarding  its  action  or  stopping  it 
altogether,  while  increased  temperature  causes  greater  activity  until 
40°  C.  is  reached,  which  is  considered  the  optimum  point.  Above 
that  mark  the  heat  becomes  injurious. 

During  the  proper  mastication  and  insalivation  of  a  mouthful 
of  food,  there  occurs,  to  the  starches  present,  a  splitting  up  into  dex- 
trin and  maltose;  the  dextrin  is  later  converted  into  maltose  also. 
This  occurs  more  quickly  with  erythrodextrin.  which  gives  a  charac- 
teristic red  color  Avith  iodine,  than  with  achroodextrin.  which  gives  na 
color  with  iodine. 

The  amylolytic  action  of  saliva  is  best  favored  by  a  neutral 
medium,  although  it  can  take  place  when  the  environment  is  slightly 
alkaline  or  acid.  The  slightest  quantity  of  free  acid  in  excess  stops 
its  action  at  once.  Its  normal  condition  in  the  mouth  is  slightly 
alkaline  or  neutral.  In  these  media  the  splitting-up  process  takes 
place  quickly ;  but,  since  the  food  is  usually  held  in  the  mouth  for  so' 
short  a  time,  all  the  starches  cannot  be  transformed  during  the  period 
of  mastication.  As  the  gastric  juice  contains  free  hydrochloric  acid, 
it  has  been  generally  thought  that  immediately  the  bolus  of  food  comes 
in  contact  with  the  gastric  juice  the  ptyalin  of  the  saliva  is  killed  and 
its  amylolytic  action  stopped.  Eecent  researches  have  proved  that  the 
transforming  continues  in  the  stomach  for  some  time  after  its  entry, 
the  time  ranging  from  fifteen  to  thirty  minutes.  That  is,  -until  (a) 
the  alkalinity  of  the  saliva  has  been  neutralized  and  (&)  until  a  trace 
of  free  hydrochloric  acid  remains  in  excess.  According  to  Veldin, 
free  hydrochloric  acid  does  not  occur  in  the  stomach  until  about 
three-fourths  of  an  hour  after  a  meal. 

The  action  of  saliva  upon  starch  is  very  readily  seen  by  test-tube 
experimentation.  In  a  tube  is  placed  a  quantity  of  boiled  starch, 
which  is  viscid  and  gelatinous  in  nature  and  rather  turbid  in  appear- 
ance. That  it  is  true  starch  may  be  shown  by  the  iodine  test,  a  blue 
color  resulting.  With  the  starch  in  the  tube  is  mixed  a  quantity  of 
saliva.  Soon  there  is  a  marked  change:  the  solution  becomes  more 
watery  and  thinner  and  the  turbidity  disappears.     On  boiling  a  por- 


DIGESTION. 


63 


tion  of  this  transparent  solution  with  Fehling's  sohition  a  cuprous 
oxide  is  precipitated,  showing  the  presence  of  sugar  in  the  form  of 
dextrose  or  maltose.  The  saliva  also  contains  traces  of  an  inorganic 
substance,  potassium  sulphocyanide.  Tincture  of  iron  stains  it  red. 
In  the  resting  serous  gland  when  stained  with  carmin  it  is  found 
that  the  cells  are  pale,  with  but  little  color,  and  contain  a  few  minute 
granules.  The  nucleus  is  small  sized,  without  a  nucleolus;  in  shape, 
irregular,  and  red  stained.  The  shrinking  of  the  nucleus  is  well 
marked.  In  the  active  stage  the  cells  are  smaller,  the  nuclei  are 
round,  with  sharp  walls  containing  nucleoli.  The  contents  of  the  cell 
are  turbid,  due  to  the  lessening  of  the  clear  substance  and  an  increase 
of  granules.     The  carmin  stains  the  cells  deeper. 

B 


^fe. 


Fig.  11.— Parotid  of  Cat.      (L.  MfLLER.)       (From  Tigerstedt's  "Human 
Physiolog}',"  copyright.  1906,  by  D.  Appleton  and  Company.) 

A,    After    fasting   24   hours.    B,    During    activity. 


The  salivary  glands  are  greatly  influenced  by  nervous  activity. 
The  submaxillary  is  supplied  by  the  chorda  tympani,  which  contains 
two  kinds  of  fibers:  the  secretory  and  the  vasodilator.  If  you  give 
atropine  you  can  paralyze  the  endings  of  the  secretory  fibers  while 
the  vasodilator  still  continue  their  activity.  Injection  of  sodium 
bicarbonate  into  the  duct  of  Wharton  arrests  the  action  of  the  secre- 
tory fibers  and  leaves  intact  the  vasodilators.  Pilocarpine  and  mus- 
carine increase  the  flow  of  saliva  by  stimulating  the  endings  of  the 
chorda  t}Tnpani  and  will  remove  the  paralysis  caused  by  atropine. 
Opium  makes  the  mouth  dry  by  acting  on  the  center  of  salivation. 
The  salivation  by  mercury  is  due  to  excessive  metabolism  of  the  gland- 
cells  themselves.  When  the  chorda  is  stimulated  by  electricity,  the 
pressure  in  the  excretory  duct  is  greater  than  tlie  blood-pressure  of  the 


64 


PHYSIOLOGY. 


animal.  During  this  stimulation  the  temperature  is  elevated.  When 
the  chorda  tymijani  is  stimulated  the  blood-vessels  of  the  gland  dilate 
and  the  veins  are  red  and  pulsate  because  the  arterial  blood  rushes 
rapidly  through  them.  The  antagonistic  nerve  which  slows  the  secre- 
tion of  saliva,  both  in  the  submaxillary  and  parotid  gland,  is  the  cer- 
vical sympathetic.  At  the  same  time,  owing  to  its  vasoconstrictors, 
the  blood-vessels  are  contracted.  Hence  in  the  submaxillary  we  have 
as  a  secretory  nerve  the  chorda  tympani ;  in  the  parotid  the  auriculo- 
temporal. The  nerve  playing  against  them  both  is  the  cervical  sympa- 
thetic. 


m    ^P^ 


B 


Fig.  12. — Parotid  of  a  Rabbit  in  Fresh  State.  (Langley.)  (From 
Tigerstedt's  "Human  Pliysiology/'  copyright,  1906,  by  D.  Appleton  and 
Company. ) 

A,  Resting  gland.     B,   Gland  after  a  small   dose  of  pilocarpin.     C,   Irritation 
of   cervical   sympathetic.     D,   After  strong   irritation   of  cervical   sympathetic. 


Trophic  and  Secretory  Fibers. 

There  are  two  kinds  of  fibers  going  to  the  salivary  glands.  If 
the  chorda  be  stimulated,  it  is  found  that  the  saliva  contains  more 
water  and  salts  in  proportion  to  the  organic  matter  than  existed 
before.  If  previous  to  the  stimulation,  the  gland  was  at  rest  and 
not  exhausted,  the  increase  of  the  stimulation  at  first  causes  a  rise 
in  the  percentage  of  organic  constituents,  and  this  rise  is  more  notable 
than  in  the  case  of  the  salts.  Hence  Heidenhain  held  that  two  kinds 
of  nerve-fibers  were  distributed  to   the  salivary  glands.     One  gov- 


DIGESTION.  65 

ems  the  secretion  of  water  and  salts,  the  other  governs  the  formation 
of  the  organic  constituents  of  the  saliva;  the  former  he  called  secre- 
tory fibers,  the  latter  trophic.  The  sympathetic  mainly  has  trophic 
fibers,  the  chorda  chiefly  secretory  fibers. 

Pawlow  has  shown  in  the  dog  that  the  submaxillary  gland  reacts 
to  a  great  number  of  stimuli,  such  as  the  sight  of  food  (psychical 
secretion),  chewing  of  meats,  and  acids.  The  parotid  reacts  only 
when  dry  food,  dry  bread  or  dry  meat,  is  placed  in  the  mouth.  Foods 
with  a  large  amount  of  water  excite  a  little  flow  of  saliva,  whilst  dry 
foods  cause  a  more  abundant  flow.  Here  is  an  adaptive  capacity  of 
the  nerves  of  the  salivary  glands  to  the  character  of  the  food  chewed. 
The  reflex  center  for  the  salivary  secretion  is  situated  in  the  medulla 
oblongata,  near  the  origin  of  the  ninth  and  seventh  cranial  nerves. 
The  afferent  nerves  are  the  nerves  of  taste,  the  chorda  tympani  and 
the  glofeso-phar}Tigeal  and  sensory  branches  of  the  trigeminus;  the 
efferent  nerves  are  the  auriculo-temporal  and  chorda  tympani. 

GASTRIC  DIGESTION     (DIGESTION  IN  THE  STOMACH). 

The  stomach  is  the  principal  organ  of  digestion.  As  we  know, 
digestion  has  for  its  aim  the  rendition  of  the  organic  and  inorganic 
substances  ingested  from  the  external  world  into  such  a  condition 
that  they  can  readily  mix  with  the  blood  and  so  be  introduced  into  the 
living  tissues  of  the  body.  For  no  animal  can  exist  which  does  not 
receive  materials  for  its  support  from  the  environing  media.  To 
accomplish  this  aim  both  chemical  and  mechanical  changes  are  closely 
interwoven.  In  the  stomach,  as  one  of  the  principal  organs,  is  per- 
formed a  large  and  important  share  of  the  whole  digestive  process ;  as 
it  were,  it  is  one  of  the  large  departments  of  a  mechanical  and  chem- 
ical laboratory  or  establishment  in  which  every  department  is  working 
toward  a  definite  end :  the  digestion  of  the  food.  Unlike  the  amylo- 
lytic  changes  of  the  saliva,  which  best  occur  in  an  alkaline  solution, 
stomachic  digestion  is  an  acid  digestion. 

The  stomach  is  the  first  organ  into  which  the  food  passes  as  it 
leaves  the  oesophagus.  It  is  the  most  enlarged  or  dilated  portion  of 
the  entire  alimentary  canal,  being  located  in  the  left  hypochondriac, 
epigastric,  and  right  hypochondriac  regions.  It  is  a  large  muscular 
pouch,  and  extends  from  the  oesophagus  to  the  small  intestine.  The 
greater  extremity  of  the  stomach  is  to  the  loft  and  communicates 
with  the  oesophagus  by  the  cardiac  orifice.  The  pyloric  end  is  the 
lesser  extremity,  and  at  the  right  communicates  with  the  small  intes- 
tine by  the  pyloric  orifice. 

5 


m 


physiol()(;y. 


The  fundus  is  the  greater  extremity  of  the  stomacli,  and  projects 
several  inches  to  the  left  of  the,  oesophagus.  The  lesser  extremity  for 
about  two  inches  of  its  length'  is  slightly  constricted,  and  is  called  the 
pyloric  antrum.  The  pyloric  orifice  is  the  entrance  to  the  duodenum, 
and  is  about  a  half-inch  in  diameter.  It  contains  the  pyloric 
sphincter,  or  valve. 

STRUCTURE  OF  THE  STOMACH. 

The  stomach  has  four  coats:  from  the  outside,  serous,  muscular, 
fibrous,  and  mucous.     The  serous  coat  is  derived  from  the  peritoneum. 

11 


Fig.   13. — Human  Stomach.      (After  Sappey.)       (From  Mills's  "Animal 
Physiologj^,"  copyright,   1889,  by  D.  Appleton  and  Company.) 

1,  CEsophagus.  2,  Circular  fibers  at  oesophageal  opening.  3,  3,  Circular 
fibers  at  lesser  curvature.  4,  4,  Circular  fibers  at  the  pylorus.  5,  5,  6,  7,  8, 
Oblique  fibers.  9,  10,  Fibers  of  this  layer  covering  the  greater  pouch.  11,  Por- 
tion of  the  stomach  from  which  these  fibers  have  been  removed  to  show  the 
subjacent  circular  fibers. 

The  muscular  coat  contains  three  layers  of  unstripod  muscular 
fibers.  The  layer  of  longitudinal  fibers  is  continuous  with  that  of 
the  oesophagus,  from  which  it  radiates  over  the  stomach. 

The  middle  laj^er  is  composed  of  circular  fibers.  These  circular 
fibers  gradually  accumulate  toward  the  pyloric  extremity  and  form  a 
thick  band  known  as  the  pyloric  sphincter.  The  internal  layer  con- 
sists of  oblique  fibers.  The  submucous  coat  is  made  up  of  areolar 
tissue  and  forms  an  extensible  layer  upon  which  the  strength  of  the 


DIGESTION. 


67 


stomach  mainly  depends.  The  mucous  membrane  of  the  stomach  is 
soft  to  the  touch  and  of  a  pale-pinkish  color.  Under  excitement  it 
becomes  reddened.  During  digestion  and  when  inflamed  it  has  a 
deep-red  hue.     It  is  thin  at  the  fundus  and  gradually  thickens  toward 


Fig.    14. — Vertical   Section   through   the  Gastric  Mucous 
Membrane.      (  Landois.  ) 

g,  g.  The  crypts  of  the  surface,  p.  The  mouths  of  the  peptic  tubules  (fundus 
glands)  with  parietal  cells  (J")  and  chief  cells  (y).  a,  v,  c,  c.  Artery,  vein,  and 
capillaries  of  the  mucous  membrane,  i.  Capillary  network  for  the  passage  of 
the  mouth  of  the  gland-duct.  (/,  '/,  The  lymphatic  vessels  of  the  mucous  mem- 
brane, passing  over,  at  e,  into  a  large  trunK  (semidiagrammatic  representation). 

the  pyloric  extremity.  In  this  place  it  ordinarily  is  in  a  state  of 
wrinkles  or  rugae,  which  are  longitudinal  in  great  part.  At  the 
pyloric  orifice  a  thick  circular  fold  acts  as  a  part  of  a  valve  called  the 
pyloric  valve. 


68  PHYSIOLOGY. 

Structure  of  Mucous  Membrane. 

Upon  an  examination  with  a  feeble  niagni lying  power  there  is 
found  on  the  mucous  membrane  a  great  number  of  depressions  about 
V200  inch  in  diameter,  which  are  the  openings  of  the  glands  of  the 
stomach.  The  mucous  membrane  is  lined  with  a  columnar  epithe- 
lium. The  tubular  glands  of  the  stomach  are  placed  side  by  side  and 
number  several  millions.  These  glands  have  a  basement  membrane, 
which  separates  the  glands  from  one  another  and  in  which  the  capil- 
laries spread  a  fine  network  over  the  tubules.  They  have  also  a  blind 
end.  There  are  two  kinds  of  gastric  glands:  the  cardiac  and  the 
pyloric.  The  pyloric  glands  have  at  their  mouth  an  epithelium  which 
is  a  continuation  of  the  columnar  epithelium  of  the  stomach.  In  the 
tubules  the  epithelium  is  shorter  and  more  cubical  and  granular.  In 
the  fundus  glands  and  cardiac  glands  the  epithelium  is  composed  of 
short  columnar  cells,  and  these  cells  have  coarser  granules  than  the 
pyloric  glands.  These  are  the  central,  or  adelomorphous,  cells.  Be- 
tween these  cells  and  the  basement  membrane  there  is  another  cell, 
oval  in  shape,  with  a  distinct  oval  granular  nucleus,  called  the 
parietal,  or  delomorphous  or  oxyntic,  cells. 

The  blood-vessels  of  the  stomach  are  derived  from  the  three  divi- 
sions of  the  coeliac  axis.  The  veins  are  the  tributaries  of  the  portal 
vein,  and  contain  numerous  valves.  The  nerves  are  the  vagus  and 
sympathetic.  Numerous  small  gangliated  plexuses  are  found:  those 
of  Meissner  in  the  submucous  coat,  like  those  in  the  intestine;  and 
Auerbach's,  between  the  muscular  fibers,  also  found  in  the  intestine. 

Movements  of  the  Stomach. 

Dr.  Beaumont,  in  experiments  upon  a  human  stomach,  ascertained 
that  a  very  feeble  peristaltic  condition  begins  at  the  cardiac  orifice,  to 
proceed  toward  the  pjdorus  by  way  of  the  greater  curvature,  for  only 
along  it  is  any  movement  apparent.  The  wave  grows  stronger  until 
the  special  band  separating  the  antrum  from  the  fundus  is  reached, 
when  the  contraction  becomes  so  strong  that  the  stomach  presents 
an  hour-glass  appearance.  Immediately  the  entire  antrum  contracts 
at  one  time  as  a  unit ;  so  that,  if  the  contents  are  properly  acted  upon 
by  the  gastric  secretion,  they  are  propelled  by  this  movement  through 
the  pylorus  into  the  duodenum.  If,  as  very  frequently  happens,  the 
semi-liquid  mass  contains  solid  portions  of  too  great  bulk  to  pass 
through  the  opening,  a  muscular  wave  is  set  up  in  the  opposite  direc- 
tion.    The  direct  result  of  this  is  to  force  into  the  fundus  through  the 


DIGESTION. 


69 


now  relaxing  temporary  sphincter  the  food-mass,  and  there  the  whole 
process  is  begun  again.  These  movements  occur  with  a  certain  degree 
of  regularity  and  rhythm,  once  in  about  every  two  or  three  minutes; 
the  time  and  regularity  are,  however,  much  influenced  by  the  quan- 
tity and  quality  of  the  food  ingested.  As  a  result  of  these  combined 
movements,  not  only  is  the  •  chymified  food  propelled  into  the  duo- 
denum, but  there  are  set  up  regular  currents  among  the  contents. 

Dr.  Cannon  has  studied  the  movements  of  the  stomach  in  cats 
by  means  of  the  Eoentgen  rays.     He  states  that  the  stomach  consists 


Fig.   15. — Gastric   Contents.      Collective  Microscopic   Picture. 
X  350.      (Leniiartz.  ) 

a,  Air-bubble.  6,  Oil-droplet,  c,  Muscle-fiber,  nearly  digested,  d,  potato 
starcb.  e,  Swollen  rye-starch,  f.  Leguminous  starch,  g.  Various  vegetable 
cells.    /(,   Vegetable  hair,     i,   Sarcina.     fc,   Yeast  fungi.     I,   Gastric  gland-cells. 


of  two  physiologically  distinct  parts :  the  pyloric  part  and  the  fundus. 
Over  the  pyloric  part  while  food  is  present  constriction  waves  are  seen 
continually  coursing  toward  the  pylorus.  The  fundus  is  an  active 
reservoir  for  the  food,  and  squeezes  out  its  contents  gradually  into  the 
pyloric  part.  The  stomach  is  emptied  by  the  formation  between  the 
fundus  and  the  antrum  of  a  tube  along  which  the  constrictions 
pass.  The  contents  of  the  fundus  are  pressed  into  the  tube  and  the 
tube  and  antrum  slowly  cleared  of  food  by  the  waves  of  constriction. 
The  constriction  waves  have  three  functions :  the  mixing,  trituration, 
and  expulsion  of  the  food.  The  stomach  movements  are  inhibited 
when  the  cat  shows  anxiety,  rage,  or  distress.     Cannon  has  observed 


70  PHYSIOLOGY. 

in  cats  that  carl)o]iydrate  food  appeared  in  the  intestine  in  ten  min- 
utes, wliilo  proteid  did  not  leave  for  an  hour.  Proteids  also  remained 
in  tli.e  stomach  twice  as  long  as  the  fats. 

CLOSURE  OF  THE  PYLORUS. 

Each  time  the  acid  chyme  escapes,  it  sets  up  a  reflex  act  which 
temporarily  occludes  the  pyloric  orifice,  and,  at  the  same  time,  inhibits 
the  propulsive  movements  of  the  organ.  The  acid  mass  of  chyme 
escaping  the  pylorus,  excites  an  increased  secretion  of  pancreatic  juice 
and  the  acid  is  gradually  neutralized.  "When  this  is  accomplished 
the  escape  of  further  acid  chyme  is  permitted.  This  regulatory 
action  prevents  disorder  in  the  progress  of  digestion  and  at  the  same 
time  insures  regularity  in  the  transition  from  the  acid  gastric  diges- 
tion to  the  alkaline  intestinal  one.  — 

THE  NERVOUS  CONTROL  OF  THE  STOMACH. 

As  known  to-day,  the  nerve-supply  to  the  stomach  is  from  both 
the  cereljro-sjjinal  system  and  the  sympathetic;  its  connection  with 
the  former  is  through  the  medium  of  the  vagi,  with  the  latter  by  the 
splanchnics  through  the  solar  plexus.  The  fibers  of  both  systems  as 
distributed  to  the  gastric  muscles  are  nonmedullated.  The  functions 
of  the  vagi  have  been  conclusively  proved  to  be  motor,  for  when  they 
are  stimulated  by  chemical,  thermal,  or  other  irritants,  there  results 
a  peristalsis  throughout  the  whole  viscus.  On  the  contrary,  the  fibers 
from  the  sympathetic  system  are  inhibitory;  when  they  are  stimu- 
lated, peristalsis  is  stopped  and  there  is  dilatation  of  the  sphincter 
pylori.  The  stomach  also  has  movements  of  its  own  independent  of 
the  central  nervous  system. 

THE  GASTRIC  JUICE. 

Gastric  juice  mixed  with  food  and  water  can  readily  be  obtained 
by  the  gastric  sound  or  stomach-pump.  Pure  gastric  juice  cannot  be 
procured  thus,  for  when  the  stomach  is  empty  the  flow  of  gastric  juice 
ceases  and  any  surplus  remaining  in  the  stomach  seems  to  be  reab- 
sorbed. Its  flow  is  begun  again  only  as  the  result  of  stimuli;  the 
natural  ones  and  those  producing  what  alone  may  be  termed  normal 
gastric  juice,  are  food  and  drink. 

ISTormal  gastric  juice  has  been  procured  by  feeding  an  animal 
a  fictitious  meal.  In  this  process  the  food  swallowed  does  not  reach 
the  stomach,  but  passes  out  of  the  oesophagus  through  a  fistula.  The 
eating  has  the  power  to  excite  reflexly  the  flow  of  the  secretion. 


DIGESTION.  71 

Gastric  juice  thus  ol)taine(l  from  a  dog  is  a  "clear,  colorless, 
limpid  fluid,  very  acid,  and  peptic  in  nature.  The  liquid  is  prac- 
tically odorless;  if  there  is  any  odor  at  all  present  it  is  characteristic 
of  the  animal.  Its  specific  gravity  differs  very  little  from  that  of 
water"  (1002.5). 

The  quantity  of  gastric  juice  secreted  daily  is  about  one-tenth 
the  weight  of  the  body. 

The  largest  constituent  of  the  gastric  juice  is  water.  In  man  and 
animals  it  is  remarkable  to  note  the  small  quantities  of  solid  matters 
present  and  then  view  the  immense  amount  of  work  done  by  them  in 
the  digestive  processes.  Of  the  solids  present,  about  half  are  inor- 
ganic salts;  the  remaining  portion  comprises  the  organic  ferment,  or 
enzyme,  present  in  gastric  juice — pepsin. 

The  reaction  of  gastric  juice  is  undoubtedly  acid,  caused  by  the 
presence  of  free  hydrochloric  acid  (0.2  per  cent.).  In  the  pure  secre- 
tion, free  from  food,  it  has  been  demonstrated  that  the  only  acid  is 
hydrochloric.  Acid  is  necessary,  for  pepsin,  the  active  ferment  of 
gastric  juice,  can  act  only  in  an  acid  medium.  During  digestion, 
lactic,  acetic,  butyric,  and  other  acids  are  often  present,  due  to  putre- 
factive changes  and  the  presence  of  liacteria.  Pepsin  can  act  in  the 
presence  of  these  acids  as  media,  but  not  very  well, 

Schmidt's  analysis  of  the  composition  of  gastric  juice  is  as 
follows : — 

Water 994.40 

Solid  residue  5.60 

1000.00 

Organic  matter : 

Pepsin    3.19 

Inorganic  matter: 

Chloride  of  sodium    1.46 

Chloride  of  potassium 0.55 

Chloride  of  calcium   0.06 

Free   hydrochloric   acid    0.20 

Phosphate  of  calcium    ^ 

Phosphate  of  magnesium L  0.12 

Phosphate  of  iron   I 

Secretion   of  the   Gastric  Juice. 

Imbedded  in  the  mucous  membrane  of  the  walls  of  the  stomach 
are  two  sets  of  secretory  apparatus:  the  cardiac  and  pyloric  glands. 
Naturally  the  products  of  these  glands  differ  somewhat  in  their  char- 
acters ;  so  that  the  gastric  secretion  as  a  unit  is  a  mixed  body,  or  solu- 


72  PHYSIOLOGY. 

tion.  This  "mixed"  gastric  juice  is  a  secretion  compound  of  a  very 
small  percentage  of  free  hydrochloric  acid  together  with  the  proteo- 
lytic ferment,  pepsin,  in  a  rather  saline  solution.  We  know  that  the 
pepsin,  for  instance,  of  the  gastric  juice,  is  not  found  as  such  in  the 
blood,  requiring  only  to  be  filtered  from  the  same  for  use,  but 
that  it  is  the  result  of  the  activity  of  the  cells  and  yielded  by  them. 

A  characteristic  microscopical  feature  of  the  cells  of  secretory 
glands  in  general  is  that  the  protoplasmic  portions  are  crowded  with 
fine  granular  bodies  before  secretion,  but  that  during  and  particularly 
after  secretion  their  numbers  are  very  perceptibly  diminished.  From 
this  it  was  inferred  that,  while  the  granules  might  not  in  themselves 
represent  the  important  ingredients  of  the  various  secretions,  yet  they 
were  responsible  and  directly  concerned  in  their  manufacture. 

The  cardiac  glands  are  composed  of  two  distinctive  types  of  cells : 
columnar  epithelium  lining  the  lumen  and  tlie  large  spherical  or 
oval  cells  located  on  the  periphery.  The  former  are  termed  cliief,  or 
central,  the  latter  parietal,  cells. 

The  pyloric  glands  are  constructed  of  but  the  one  kind,  epithelial 
in  nature,  similar  to  those  found  in  the  cardiac  cells  and  termed 
cliief,  or  central. 

The  central  cells  of  both  the  cardiac  and  pyloric  glands  are  found 
to  be  heavily  charged  with  minute  granules  before  digestion ;  in  fact, 
such  numbers  are  present  as  to  interfere  with  the  staining  of  the  cells 
with  aniline  dyes,  because  of  the  protoplasm  being  obscured.  During 
secretion  some  of  the  granules  are  discharged  into  the  lumen,  pre- 
sumably through  the  protoplasmic  movements  of  the  cells  as  agents 
or  media.  After  digestion,  therefore,  the  cells  show  a  difference, 
principally  in  that  there  is  a  decrease  in  the  number  of  granules 
present,  manifested  by  either  a  clear  path  along  the  periphery  or  by  a 
shrunken  appearance  of  the  cells  with  fewer  granules.  The  material 
for  the  formation  of  these  granules  is  taken  by  the  cells  from  the 
lymph  which  constantly  bathes  them,  and  through  the  influence  of  the 
protoplasm  is  manufactured  into  granules. 

The  central  are  the  cells  which  are  directly  concerned  in  yielding 
the  very  important  and  proteolytic  element  of  the  gastric  juice,  the 
pepsin.  Without  its  presence  in  an  acidulated  medium,  the  normal 
processes  of  proteolysis  are  unable  to  be  accomplished  in  the  stomach. 
These  granules  are  not  pure  pepsin  to  be  passed  along  the  lumen  and 
so  enter  the  composition  of  the  gastric  juice,  but  are,  rather,  a  zymo- 
gen substance  acting  as  a  precursor,  which  is  readily  converted  into 


DIGESTION.  73 

pepsin   through   the    influence   of   the   acid.     To    this   intermediate 
substance  has  been  given  tlie  name  pepsinogen. 

The  hirge  oval  or  parietal  cells  also  contain  granules  which  are 
very  few  in  number  and  small  in  size,  though  quite  distinct.  These 
are  very  constant  in  quantity,  the  cells  showing  mainly  differences  in 
size.  Thus,  before  secretion,  they  are  swollen;  afterward,  shrunken. 
They  are  frequently  termed  oxyntic,  as  they  are  thought  to  secrete 
hydrochloric  acid,  one  of  the  essential  compounds  of  the  gastric  secre- 
tion. The  exact  process,  however,  is  still  shrouded  in  mystery.  It 
is  thought  to  result  from  a  simple  process  of  diffusion  in  the  parietal 
cells  of  chlorides  taken  from  the  blood,  for  during  secretion  the 
quantity  of  chlorides  leaving  the  blood  through  the  kidneys  is  dimin- 
ished. Maly's  theory  with  regard  to  this  is  very  satisfactory.  In  it 
he  claims  that  the  acid  originates  by  the  interaction  of  the  calcium 
chloride  with  the  disodium  hydrogen  })hosphate  of  the  blood.  The 
interaction  is  simplified  by  the  following  equation  of  Maly's: — 

2NaoHP0,  +  3CaCL  =  Ca3(P0,),  +  -^lUVX  +  2HC1 


Disodium 

Calcium 

Calcium 

Sodium 

Hydro- 

hydrogen 

chloride. 

phosphate. 

chloride. 

chloric 

phosphate. 

acid. 

The  stimulus  to  the  secretion  of  HCl  is  the  presence  of  free 
chlorine  ions  on  the  inner  side  of  the  stomach's  glands.  If  chlorine 
ions  are  absent  in  the  stomach  then  no  HCl  is  formed.  If  the  ani- 
mal be  fed  on  bromides  instead  of  chlorides,  then  hydrobromic  acid 
is  formed  in  place  of  HCl.  The  glands  of  the  stomach  do  not  permit 
chlorine  ions  to  go  through  them,  whilst  free  hydrogen  ions  which 
exist  in  the  blood  go  through  the  glands  into  the  stomach  and  HCl 
is  formed. 

Formed  in  the  central  cells  is  another  zymogen  than  pepsinogen, 
which,  when  mixed  with  acid,  produces  an  enzyme,  or  ferment,  known 
as  rennin.  This  ferment  has  the  power  to  coagulate  milk,  forming 
casein.  Eennin  is  found  wherever  pepsin  is  manufactured,  although 
distinctly  different  in  character  and  action. 

The  fluid  is  not  poured  out  at  the  same  rate  from  the  beginning 
to  the  end  of  digestion.  The  Mett  method  of  preparing  the  proteid  is 
to  fill  a  glass  tube,  one  to  two  millimeters  in  diameter,  with  egg- 
albumin  and  coagulate  it  at  95°  C.  The  tube  is  then  cut  into  small 
pieces  and  placed  in  1  or  3  cul)ic  centimeters  of  the  juice  to  be  investi- 
gated. The  law  of  Schuetz  is  as  follows :  the  quantity  of  pepsin  in 
the  compared  liquids  is  proportionate  to  the  square  of  the  rapidity  of 
digestion;  that  is,  the  square  of  the  column  of  proteid  in  a  Mett  tube 


74 


PHYSIOLOGY. 


expressed  in  millimeters  which  ihe  juices  are  capable  of  digesting  in 
the  same  period  of  time.  If  one  of  the  fluids  digest  a  column  of  2 
millimeters  of  proteid  and  the  other  a  column  of  3  millimeters,  the 
relative  quantity  of  pepsin  in  each  is  not  expressed  by  the  figures  3 
and  3,  respectively,  but  by  the  squares  of  them ;  that  is,  4  and  9 ; 
so  that  the  second  liquid  is  two  and  one-fourth  times  stronger  than 
the  first. 

Not  only  the  quantity  of  the  secretion  varies,  but  the  secretion 
varies  in  composition  with  a  greater  or  less  quantity  of  ferment. 
Other  properties  of  the  juice  are  likewise  varied.     In  one  and  the 


Meat. 

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read. 

Milk 

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Fig.  IG. — Hourly  Variations  of  the  Secretion  of  C4astric  Juice  in  the  Dog 
after  a  Meal  of  Meat,  Bread,  and  Milk.      (Pawlow.) 

same  juice  the  dilferont  ferments  nuiy  suffer  variations,  running 
courses  independently  of  each  other,  a  fact  which  undoubtedly  shows 
that  the  pancreas,  which  has  a  complex  chemical  activity,  is  able  to 
furnish,  during  given  periods  of  its  secretory  work,  now  one  pro- 
duct and  now  another.  That  which  may  be  said  of  the  ferments 
may  also  be  applied  to  the  quantities  of  the  salts  in  the  juices.  The 
gastric  juice  always  has  the  same  acidity  as  poured  out  by  the  glands, 
but  on  leaving  the  glands  and  running  over  the  walls  of  the  stomach, 
the  mucus  can  neutralize  25  per  cent,  of  it.  The  food  also  neutralizes 
the  acid. 

At  the  beginning  of  digestion,  when  the  quantity  of  food  is  large 
and  its  external  structure  still  coarse,  the  strongest  juice  should  be 
poured  out  when  most  needed.  The  greatest  digestive  power  belongs 
to  the  juice  poured  out  on  bread,  which  mio;ht,  for  brevity,  be  called 


DIGESTION. 


75 


"bread-juice";  the  next  strongest  is  "flesh-juice/'  and  then  comes 
"milk-juice."  In  other  words,  "bread-juice"  contains  four  times  as 
much  ferment  as  "milk-juice."  Xot  alone  the  digestive  power,  but 
likewise  the  total  acidity,  varies  according  to  the  nature  of  the  diet. 
Comparing  equivalent  weight,  flesh  requires  the  most  and  milk  the 
least  gastric  juice;  but  taking  equivalents  of  nitrogen,  bread  needs 
the  most  and  flesh  the  least.  The  hourly  intensity  of  gland  work  is 
almost  equal  in  the  case  of  milk  and  flesh  diets,  but  far  less  with 
bread.  The  bread,  however,  exceeds  all  others  in  the  time  required 
for  its  digestion,  and  the  duration  of  the  secretion  is  correspondingly 
protracted. 


s  .^ 


1^ 


Fig.  17. — Hourly  Variations  of  the  Digestive  Power  of  the  Gastric 
Juice  in  the  Dog  after  a  Meal  of  Meat,  Bread,  and  Milk.  (Pawlow, 
Gley.  ) 


M 

cnf 

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id. 

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Each  separate  kind  of  food  corresponds  to  a  definite  hourly  rate 
of  secretion,  and  calls  forth  a  characteristic  alteration  of  the  proper- 
ties of  the  juice.  Thus,  with  flesh  diet,  the  maximum  of  secretion 
occurs  during  the  first  or  second  hour,  and  in  both  the  quantity  of 
juice  furnished  is  approximately  the  same.  With  bread  diet  we  have 
always  a  sharply  indicated  maximum  in  the  first  hour,  and  with  milk 
a  similar  one  during  the  second  or  third  hour.  On  the  other  hand, 
the  most  active  juice  occurs  with  flesh  in  the  flrst  hour,  with  bread 
in  the  second  and  third  hours,  and  with  milk  in  the  last  hour  of  secre- 
tion. The  point  of  maximvim  outflow  as  well  as  the  whole  curve  of 
secretion  is  always  characteristic  for  each  diet.  On  proteid  in  the 
form  of  bread,  five  times  more  pepsin  is  poured  out  than  on  the  same 
quantity  of  proteid  in  the  form  of  milk,  and  the  flesh-nitrogen  re- 
quires 25  per  cent,  more  pepsin  than  that  of  milk.     These  different 


7(3  PHYSIOLOGY. 

kinds  of  protoid  receive,  therefore,  quniitities  of  ferment  correspond- 
ing to  the  dilferences  in  llieii-  digestil)ility,  which  we  already  know 
from  experiments  in  pliysiological  chemistry. 

Excitants  of  Flow  of  Gastric  Juice. 

Before  the  dog  adapted  for  sham  feeding,  Pawlow  cut  up  meat 
and  sausage,  when  he  obtained  a  great  flow  o,f  gastric  juice,  more  so 
than  when  he  fed  the  dog  with  them ;  they  escaped  by  the  oesophagus. 
Here  is  a  psychic  excitation  of  the  gastric  secretion,  which  plays  a 
considerable  part  in  the  production  of  gastric  juice  in  the  sham  feed- 
ing experiment. 

The  appetite  is,  then,  the  first  and  mightiest  exciter  of  the  secre- 
tory nerves  of  the  stomach.  A  good  appetite  in  eating  is  equivalent 
from  the  outset  to  a  vigorous  secretion  of  the  strongest  gastric  juice. 
Sham  feeding  of  five  minutes  does  not  call  forth  a  secretion  for  longer 
than  three  to  four  hours. 

Mechanical  excitation  of  the  mucous  membrane  of  the  stomach 
does  not  cause  the  flow  of  gastric  juice.  Sodium  bicarbonate  in  the 
stomach  inhibits  its  secretion.  Liebig's  extract  or  meat-broth  intro- 
duced into  the  stomach  increases  the  secretion  of  gastric  juice.  Fat 
in  the  stomach  inhibits  the  psychic  secretory  action  of  the  stomach 
upon  meat.  The  fat  of  milk  can  inhibit  its  digestion  to  a  certain 
extent. 

The  secretory  activity  of  the  stomach  depends  on  nervous  pro- 
cesses. In  the  immense  majority  of  cases  gastric  digestion  begins  by 
a  strong  central  excitation  of  the  secretory  and  trophic  fibers  of  the 
glands. 

Popielski  has  shown  that  a  stomach  with  all  nervous  connections 
severed  will  secrete  gastric  juice,  if  extracts  of  meat  are  placed  in  the 
stomach.  Edkins  believes  this  secondary  secretion  of  gastric  juice 
to  be  due  to  the  action  of  the  products  of  digestion  on  the  pyloric 
mucous  membrane.  They  produce  in  the  membrane  a  chemical  sub- 
stance, which  is  absorbed  into  the  circulation,  and,  conveyed  to  the 
glands  of  the  stomach,  it  acts  as  a  specific  excitant  of  their  secretory 
activity.  Starling  calls  it  a  gastric  secretion  or  gastric  hormone, 
similar  to  the  secretin-exciting  pancreatic  secretion. 

Secretory  Nerves  of  the  Stomach. 

In  a  dog  with  a  cannula  in  the  stomach  and  the  oesophagus 
opened  so  that  food  leaving  the  mouth  goes  through  the  opening  in 
the  oesophagus,  and  not  into  the  stomach  ("sham  feeding"),  the  swal- 


DIGESTION. 


lowing  of  food  caused  a  great  increase  of  flow  of  gastric  juice.  If, 
now,  the  pulmonary  and  abdominal  vagi  are  divided  on  both  sides, 
then  sham  feeding  causes  no  flow  of  gastric  juice.  These  experiments 
show  that  the  gastric  glands  receive  their  normal  impulses  to  activity 
by  means  of  nerve-fibers  in  the  vagi.  Pawlow  believes  that  secretory 
nerves  of  the  stomach  run  in  the  vagi.  Pawlow  also  excited  the  vagi 
after  a  previous  section  for  some  days  and  obtained  an  increase  of 


Pylorns 

Plexus  gastricui 
Anterior  vagi 


CEsophagns 


II. 


Fig.   18. — Dog's  iStomaeh.      (Pawlow.) 

I.    A-B,     Line  of  incision.     C,   Flap  for  forming  stomach-pouch   of  Pawlow. 
II.     1',  Cavity  of  large  stomach.    S,  Pawlow's  pouch,  or  small  stomach.    A,  A, 
Abdominal   wall. 

gastric  secretion.  Atropine  paralyzes  the  secretory  nerves  of  the 
stomach.  By  the  secretory  fibers  we  mean  those,  according  to  Heid- 
enheim,  which  stir  up  the  secretion  of  water  and  inorganic  salts  of 
the  gastric  juice.  The  trophic  fibers  are  concerned  in  the  secretion  of 
the  ferment  of  the  gastric  juice.  Sooner  or  later  after  the  taking  of 
food  the  influence  of  the  reflex  excitant  comes  into  play,  while  the 


78  PHYSIOLOGY. 

psychic  effect  dies  out.  If  meat  has  been  eaten,  the  secretory  center 
will  still  be  strongly  excited  in  a  reflex  manner  from  the  stomach  and 
intestine,  while,  at  the  same  time,  the  trophic  center  receives  only 
weak  impulses  from  the  peripheral  terminations  of  the  nerves  in  ques- 
tion. When  bread  is  eaten  the  reverse  happens.  After  the  cessa- 
tion of  the  psychical  stimulus,  the  secretory  fibers  are  now  only  weakly 
excited  through  the  end-apparatus;  the  trophic,  on  the  other  hand, 
are  strongly  influenced.  In  the  case  of  fat  foods  reflex  inhibitory 
impulses  proceed  to  the  centers  which  affect  the  activity  of  both  secre- 
tory and  trophic  nerves. 

ACTION  OF  AGENTS  ON  THE  STOMACH. 

When  absolute  alcohol  or  a  strong  emulsion  of  oil  of  mustard  was 
introduced  in  the  small  stomach  (Pawlow),  there  was  an  enormous 
secretion  of  mucus. 

Ice-cold  water  in  the  large  stomach  (Pawlow)  causes  the  secre- 
tion, which  is  subsequently  produced  by  an  ordinary  meal,  to  be  less 
than  normal,  more  especially  in  the  first  hour;  here  is  a  special 
inhibitory  reflex. 

When  alcohol  is  poured  into  the  large  stomach  (Pawlow)  an 
extremely  free  secretion  of  gastric  juice  Ijegins  in  the  small  stomach 
(Pawlow).  The  secretion  in  the  small  stomach  was  compensatory 
for  the  arrested  secretion  in  the  large  stomach. 

In  hypersecretion  of  the  stomachs  of  dogs  he  found  sodium  bicar- 
bonate to  have  a  good  effect.  In  hyposecretion  he  found  water  a 
good  agent. 

Borrisow  has  shown  that  bitter  substances,  such  as  gentian,  excite 
the  flow  of  gastric  juice. 

Hydrochloric  acid,  when  secreted  in  considerable  quantity,  pre- 
vents further  secretion  of  gastric  juice.  Phosphoric  acid  does  not 
inhibit.     Butyric  acid  strongly  excites  gastric  secretion. 

ACTION  OF  THE  GASTRIC  JUICE. 

The  amylolytic  action  of  the  saliva,  the  conversion  of  starch  into 
maltose,  is  dependent  upon  the  presence  of  ptyalin,  an  organic  fer- 
ment whose  actipn  is  best  carried  on  in  a  neutral  or  alkaline  medium. 
The  proteolytic  action  of  the  gastric  juice  is  due  to  the  presence  of  its 
organic  ferment,  or  enzyme, — pepsin, — in  an  acid  medium.  A  par- 
tial digestion  of  certain  foodstuffs  can  be  accomplished  in  an  acid 
solution,  if  given  sufficient  time  and  the  proper  temperature.  There 
is,  however,  a  strong  tendency  toward  putrefaction  during  the  pro- 


DIGESTION. 


79 


cess.  On  the  other  hand,  pepsin  alone  is  unable  to  perform  any  dis- 
solution or  digestion  of  the  foods  with  which  it  comes  into  contact. 
But,  if  to  it  a  0.2-per-cent.  solution  of  hydrochloric  acid  is  added, 
proteolysis  proceeds  quickly  and  energetically.  The  powers  of  the 
gastric  juice  cannot  ])e  attributed  to  the  presence,  then,  of  its  acid  or 
pepsin  alone,  but  to  a  combination  which  may  be  termed  pepsin-acid. 
Thus  gastric  digestion  is  an  acid  digestion,  and  demands  a  knowledge 


Fig.  19. — Dogs  to  whom  a  Fictitious  Meal  is  Given.  They  have  a 
fistula  in  the  ossophagus  and  a  fistula  in  the  stomach.  After  a  photo- 
graph taken  in  the  laboratory  of  Pawlow.      (Gley.  ) 

of  chemistry,  for  it  is  in  many  respects  a  chemical  act.  The  result 
of  the  action  of  gastric  juice  on  food  is  essentially  the  same  whether 
the  act  takes  place  within  the  body  or  outside  of  it.  Life  has  nothing 
to  do  with  it,  for  it  is  a  chemical  action  on  the  protcids  of  the  food. 
In  the  stomach,  then,  the  main  process  of  digestion  is  the  conversion 
of  the  proteids,  through  intermediate  stages,  into  peptones,  for  pro- 


80  PHYSIOLOGY. 

teids  are  incapable  of  diffusion  through  animal  meml>ranes  in  the 
act  of  absorption. 

Thus  it  can  safely  be  stated  tliat  tlie  prime  and  essential  func- 
tion of  the  gastric  secretion  is  to  dissolve  the  proteids  present  and 
convert  them  inio  peptones. 

Gastric  juice  exercises  no  amylolytic  influences  upon  any  starch 
present;  in  fact,  three-fourths  of  an  hour  after  a  meal,  the  action 
going  on  due  to  the  saliva  swallowed  with  the  food  is  stopped  alto- 
gether by  reason  of  traces  of  free  hydrochloric  acid  secreted  by  the 
oxyntic  cells. 

There  is  a  fat-splitting  ferment  in  the  gastric  juice  of  the  fundus. 

Those  mineral  matters  which  can  be  dissolved  in  hydrochloric 
acid  of  the  strength  of  that  found  in  the  gastric  juice  are  also  dis- 
solved in  the  stomach.  The  degree  of  solubility  and  efficiency  at- 
tained by  the  gastric  secretion  far  surpasses  that  of  simple,  diluted 
acid,  probably  because  of  the  pepsin  found  in  the  former. 

Although  the  amylolytic  action  of  the  saliva  on  starch  takes  place 
for  a  definite  interval,  the  gelatinous  envelopes  of  the  fat-globules  and 
mineral  substances  are  dissolved  within  the  receptacle  of  the  stomach, 
yet  the  essential  and  characteristic  feature  of  the  work  to  be  done 
there  is  on  the  proteids:  converting  them  into  peptone  through  the 
action  of  proteolysis. 

The  proteids  found  in  Nature  are  very  complex  and  as  yet  not 
thoroughly  known.  However  much  they,  as  individuals,  may  difEer 
in  composition,  reactions,  etc.,  yet  they  all  possess  an  inherent  ten- 
dency to  undergo  hydrolytic  decomposition  when  conditions  are  favor- 
able. Hydration  and  cleavage  can  be  induced  by  simple  heating  in 
water  alone  raised  to  the  temperature  of  100°  C,  for  there  results  par- 
tial solution  of  the  proteids  during  the  process.  The  proteolytic  pro- 
cess of  the  gastric  secretion  in  its  converting  proteids  into  peptones 
is  also  one  of  Jiydration  and  cleavage.  The  final  products  are  not  the 
result  of  one  simple  step,  not  the  formation  of  one  simple  body  or 
substance,  as  when  the  proteids  are  acted  on  by  heated  water  alone. 
The  acid  in  gastric  digestion  induces  a  row  of  chemical  changes  and 
products,  each  separate  and  distinct,  and  capable  of  being  recognized 
by  certain  reagents. 

By  the  action  of  pepsin-acid  the  proteid  is  first  changed  into  (1) 
syntonin,  or  acid-alhumin.  By  further  action  of  the  ferment,  the 
acid-albumins  are  changed  into  (2)  proteoses,  with  their  divisions  into 
primary  and  secondary  proteose.  The  proteoses  are  the  intermediate 
products  between  acid-albumins  and  peptones.     These  are  found  un- 


DIGESTION.  81 

der  various  names  in  this  group;  as,  the  proteoses  may  be  derived 
from  albumin,  when  they  are  called  albumoses;  or  from  globulin, 
when  the  name  globuloses  is  used.  The  proteoses  are  soluble  in  warm 
water,  acids,  and  the  alkalies.  They  are  only  slightly  diffusible  and 
not  coagulated  by  the  action  of  heat.  Nitric  acid  produces  a  white 
precipitate,  which  is  colored  yellow  by  heat  and  dissolved  again. 
When  cool,  the  precipitate  occurs  again ;  this  recurrence  of  the  pre- 
cipitate upon  cooling  is  a  distinctive  feature  of  proteoses.  Ammo- 
nium sulphate  precipitates  proteoses  and  leaves  the  peptones  in 
solution. 

By  the  continued  proteolytic  action  of  the  gastric  juice,  the 
proteoses  are  changed  into  (;3)  peptones,  the  final,  diffusible  products 
of  gastric  digestion.  They  are  simply  the  result  of  a  process  of 
hydration. 

The  peptones  are  very  diffusible,  particularly  in  acid  solution. 
The  utility  and  benefit  to  be  derived  from  that  characteristic  is  very 
evident  when  we  keep  in  mind  the  chief  aim  of  digestion,  which  is  to 
render  foodstuffs  into  soluble  conditions  so  that  they  may  be  readily 
absorbed  and  so  become  a  component  of  the  blood  and  eventually  of 
the  tissues. 

The  peptones  are  soluble  in  water,  but  not  precipitated  from 
their  aqueous  solutions  by  the  addition  of  acids  or  alkalies,  or  by  boil- 
ing. In  fact,  peptones  are  never  coagulated  by  heat.  They  are  not 
precipitated  by  nitric  acid,  copper  sulphate,  ammonium  sulphate,  and 
a  number  of  other  reagents  usually  held  as  precipitants  of  proteids. 

To  differentiate  albumoses  from  peptones,  add  a  few  drops  of 
salicyl-sulphonic  acid  to  several  cubic  centimeters  of  the  original  fluid. 
A  white  precipitate  may  indicate  native  proteid  or  proteoses.  Boil, 
then  the  proteoses  dissolve,  whereas  the  native  proteid  becomes 
coagulated.  Filter  hot.  If  a  precipitate  forms  in  the  filtrate  on 
cooling,  it  indicates  proteoses.  Filter  off  this  precipitate  and  apply 
the  biuret  test  to  filtrate.     A  rose-pink  coloration  indicates  peptone. 

However,  the  chief  and  striking  feature  of  peptones  is  their  great 
diffusibility.  Other  forms  of  proteid  matter  pass  through  animal 
membranes  with  very  great  difficulty,  if  at  all. 

When  the  proteids  have  lieen  reduced  to  peptones,  they  are  ready 
for  absorption  into  the  blood  through  the  capillary  walls.  However, 
proteoses,  the  intermediate  products,  although  less  diffusible  than 
peptones,  find  their  way,  to  souie  extent,  also,  through  the  capillary 
walls.  Experiment  has  demonstrated  that  pure  proteoses,  or  even 
peptones,  introduced  directly  into  the  blood  are  more  or  less  toxic, 

6 


82  PHYSIOLOGY. 

and  the  system  behaves  toward  them  as  foreign  bodies,  striving  to  get 
rid  of  them  as  speedily  as  possible.  From  this  it  is  evident  that 
there  must  be  some  transformation  in  the  very  act  of  diffusion  through 
the  capillary  walls,  else  the  nutritions  proteid  matters  are  not  used  in 
constructive  metamorphosis,  but  expelled  as  foreign  matters.  The 
agencies  which  act  upon  these  proteoses  and  peptones,  in  some  manner 
destroy  their  toxic  tendencies  and,  probably,  convert  them  into  the 
serum-albumin,  or  globulin,  of  the  blood.  The  fact  that  peptones  are 
not  found  in  the  blood  and  lymph  during  or  directly  after  digestion 
confirms  this  idea,  since  peptones  are  absorbed  as  soon  as  manu- 
factured. An  excess  of  peptone  in  the  stomach-contents  would  have 
the  power  to  arrest  proteolysis  by  its  mere  presence.  A  preparation 
on  the  market  is  somatose,  a  mixture  of  albumoses  produced  by  the 
action  of  a  ferment  on  meat.  It  is  a  predigested  beef,  and  readily 
absorbed.  It  dispenses  with  the  large  amount  of  fluid  which  is  neces- 
sary in  peptonized  milk. 

Weinland  has  shown  that  the  epithelium  of  the  stomach  and  of 
the  intestines  forms  antipepsin  and  antitrypsin,  which  prevent  diges- 
tion of  the  stomach  itself  or  of  the  intestine,  by  the  ferments,  pep- 
sin and  trypsin. 

Antiseptic  Action  of  the  Hydrochloric  Acid  in  Gastric  Juice. 

Besides  the  function  which  hydrochloric  acid  exercises  as  a  com- 
ponent of  the  gastric  secretion. — namely:  of  rendering  the  pepsin 
in  it  active, — it  possesses  another  very  powerful  property  as  a  dis- 
infectant and  germicide  in  that  it  can  kill  many  bacteria  that  are 
taken  in  with  the  food.  By  means  of  it  the  bacteria  producing 
putrefaction  are  killed,  and  thus  disorders  in  the  entire  constitution 
as  a  result  of  abnormal  digestion  are  prevented.  Even  when  putre- 
faction has  occurred  in  the  food  previous  to  its  entrance  into  the 
stomach,  upon  reaching  this  receptacle  it  is  stopped. 

Many  pathological  bacteria  are  likewise  destroyed  by  the  acid  in 
the  juice,  although  some,  as  the  bacillus  of  tuberculosis  and  that  of 
splenic  fever,  are  unaffected.  It  is  interesting  to  note  that  experi- 
ment has  shown  that  just  about  the  amount  and  strength  of  hydro- 
chloric acid  as  that  in  the  stomach  is  needed  outside  the  body  to  ac- 
complish the  death  of  putrefactive  and  many  pathological  germs. 
Acetic  and  lactic  fermentations  are  arrested  by  mere  traces  of  hydro- 
chloric acid. 

To  epitomize:     The  general  action  of  gastric  juice  is  to  convert 


DIGESTION.  83 

the  proteids  into  peptones  by  various  stages.  The  fats  are  split  up 
b}^  a  gastric  lipase.     Starch  is  unaffected. 

The  general  result  is  the  formation  of  a  pouplike  mass  in  the 
stomach.  This  undigested  food  is  passed  through  the  pylorus  into 
the  duodenum  of  the  small  intestine,  and  is  called  chyme.  The 
average  time  that  food  remains  in  the  stomach  is  about  three  hours. 

Giinzburg's  Test  for  Hydrochloric  Acid. — With  a  solution  of 
phlorogluciu  and  vanillin  in  alcohol  mix  a  drop  of  a  solution  of 
hydrochloric  acid.  0.2  per  cent. ;  evaporate  slowly  in  a  porcelain  cap- 
sule, when  a  red  color  will  appear. 

TJffelmann's  Test  for  Lactic  Acid. — Add  a  trace  of  solution  of 
ferric  chloride  to  a  1-per-cent.  solution  of  carbolic  acid.  This  ame- 
thyst-colored solution  will  change  to  canary  yellow  on  the  addition 
of  lactic  acid. 

VOMITING. 

Vomiting  is  a  spasmodic  rejection  of  food  from  the  stomach,  and 
is  usually  a  sign  of  some  malady.  The  ease  with  which  animals  vomit 
is  dependent  upon  the  conformation  of  the  stomach,  particularly  with 
regard  to  the  fundus,  as  well  as  the  condition  of  its  contents.  Thus, 
a  child  vomits  easily,  since  its  fundus  is  not  very  well  developed; 
with  the  adult  the  act  is  one  of  great  difficulty. 

When  the  person  is  conscious,  vomiting  is  usually  preceded  by  a 
sensation  of  nausea,  during  which  the  saliva  flows  very  freely  into 
the  mouth.  While  the  food  is  being  swallowed  considerable  air  enters 
the  stomach,  and  later  assists  actual  vomiting  by  helping  to  dilate  the 
cardiac  orifice.  Before  the  real  expulsion  occurs,  and  during  the 
efforts  to  accomplish  the  same,  a  very  deep  inspiration  is  taken  just 
as  in  the  act  of  coughing.  Immediately  the  glottis  closes,  and  the 
muscles  of  the  abdomen  commence  to  contract  very  actively.  In- 
stead of  the  glottis  opening  to  permit  an  expiration,  it  remains  tightly 
closed,  thereby  holding  the  diaphragm  immovably  fixed,  and  so 
furnishing  an  unresisting  plane  against  which  the  stomach  is  pressed. 
Immediately  preceding  the  pressure  brought  to  bear  upon  the 
stomach  by  the  contraction  of  the  abdominal  muscles,  there  occurs 
a  shortening  of  the  longitudinal  fibers  of  the  oesophagus,  thereby 
bringing  the  cardiac  orifice  of  the  stomach  nearer  the  diaphragm, 
to  form  a  straight  passageway  for  the  vomit  to  the  phar}Tix.  The 
muscles  of  the  sphincter  at  the  cardiac  orifice  are  rather  suddenly 
dilated,  forming  a  funnel-shaped  opening  at  the  beginning  of  escape, 
since   the  pylorus  usually  remains   closed.     By  the  abdominal   con- 


84  PHYSIOLOGY. 

tractions  and  slightly  assisted  by  gastric  movements  also,  some  of  the 
contents  of  the  stomach  is  forced  into  the  opening  of  the  oesophagus, 
where  its  movement  toward  the  pharynx  and  mouth  is  aided  by  con- 
tractions of  the  oesophageal  circular  fibers :  the  reverse  of  what  occurs 
when  a  bolus  of  food  is  swallowed. 

Thus  there  are  two  separate  and  distinct  acts  occurring  during 
vomiting:  (a)  the  dilating  of  the  cardiac  sphincter  and  (b)  the 
expulsive  movements  of  the  abdominal  muscles.  The  absence  of 
either  act  is  detrimental  to  the  accomplishment  of  vomiting.  The 
pyloric  gate  is  usually  closed  during  vomiting;  so  that  little  or  no 
substances  find  their  way  into  the  duodenum.  However,  when  the 
gall-bladder  is  very  full,  the  movements  of  the  surrounding  organs 
force  its  contents  into  the  duodenum  and  very  frequently  some  of  the 
bile  finds  its  way  into  the  stomach,  from  whence  it  passes  out  through 
the  oesophagus,  pharynx,  and  mouth  in  bilious  vomiting, 

That  the  expulsive  impetus  is  mainly  given  by  the  contractions 
of  tlie  abdominal  walls  and  not  the  gastric  movements  alone  has  been 
proved  by  experiment.  The  stomach  of  an  animal  was  excised  and 
replaced  with  a  bladder  filled  M'ith  water  and  attached  to  the  oesoph- 
agus by  means  of  a  rubber  tul)e.  When  tlie  wound  was  closed  and 
an  emetic  injected,  the  contents  of  the  bladder  were  immediately 
expelled  through  the  mouth. 

Vomiting  is  normally  considered  to  be  a  reflex  action,  although 
in  some  instances  vomiting  may  proceed  at  will  or  be  acquired  after 
some  practice.  The  afferent  nerves  are  principally  the  fiftJi.  the 
glosso-pharyngeal,  and  the  vagus.  The  center  of  vomiting  is  located 
in  the  medulla  oblongata.  The  efferent  impulses  are  conveyed  by  the 
vagi  to  the  stomach,  phrenics  to  the  diaphragm,  and  various  spinal 
nerves  to  the  abdominal  muscles.     Thus  vomiting  may  arise: — 

1.  From  irritation  of  the  stomach,  as  when  this  organ  is  too  full. 

2.  From  tickling  the  vault  of  the  palate. 

3.  From  intestinal  irritation  by  worms. 

4.  From  irritation  of  the  uterine  mucous  membrane  during  the 
first  three  months  of  pregnancv. 

5.  The  remembrance  or  siglit  of  disgusting  sights,  or  pathological- 
disorders  of  the  brain  may  cause  it,  which  proves  that  the  brain  is 
united  to  a  vomiting  center. 

6.  The  use  of  emetics,  which  do  not  all  act  alike. 

Thus,  some  emetics,  as  copper  sulphate,  mustard,  etc.,  produce 
emesis  because  of  their  irritating  effects  upon  the  peripheral  nerves 


DIGESTION.  85 

in  the  mucous  membrane  lining  the  stomach.  Others,  like  tartar 
emetic,  apomorphine,  etc.,  attain  the  same  results  by  reason  of  their 
•  stimulating  the  vomiting  center  in  the  medulla. 

DIGESTION  IN  THE  INTESTINES. 

When  the  food  is  converted  into  chyme  and  partially  dissolved 
by  the  gastric  juice,  it  passes  into  the  small  intestine,  where  it  is 
subjected  to  new  reagents:  the  bile,  pancreatic  juice,  and  intestinal 
juices.  Here  the  food  is  prepared  for  absorption,  forming  what  is 
called  chyle,  which  is  rapidly  taken  up  by  the  chyliferous  vessels. 

Because  of  the  small  and  large  calibers  of  the  two  parts  of  the 
intestinal  tract,  the  portions  have  received  the  names  of  sinall  and 
large  intestines,  respectively.  The  small  intestine,  the  continuation 
of  the  stomach,  opens  into  the  large  intestine  by  an  orifice  which  is 
guarded  by  the  ileo-ccecal  valve.  Under  ordinary  and  normal  condi- 
tions this  valve  allows  the  passage  of  the  remnants  of  active  digestion 
to  pass  through  from  the  small  into  the  large  intestine;  very  rarely 
does  the  reverse  occur,  except  in  some  cases  of  hernia  and  other  ob- 
structions in  the  large  intestine. 

THE  SMALL   INTESTINE. 

This  tube  is  cylindrical  and  much  convoluted.  It  occupies  the 
umbilical  region  and  is  suspended  from  the  vertebral  column  by  the 
mesentery.  It  measures  about  twenty-five  feet  in  length,  and  its 
diameter  is  about  one  and  three-fourths  inches.  As  it  continues  to 
join  the  large  intestine  it  becomes  slightly  narrower.  It  consists  of 
three  parts:    the  duodenum,  jejunum,  and  ileum.. 

The  duodenum  is  twelve  fingers'  breadth  in  length,  and  it  is 
the  widest  part  of  the  small  intestine.  It  commences  at  the  pyloric 
end  of  the  stomach  and  opposite  the  second  lumbar  vertebra;  it 
terminates  in  the  jejunum.  The  common  bile-duct  and  the  pan- 
creatic duct  perforate  the  inner  side  of  the  duodenum. 

The  jejunum  constitutes  about  two-fifths  of  the  small  intestine. 
It  is  wider  than  the  ileum  and  is  characterized  by  the  absence  of  the 
agminated  glands.  The  ileum  constitutes  three-fifths  of  the  small 
intestine,  and  terminates  in  the  right  iliac  region  by  joining  the  large 
intestine  at  a  right  angle. 


8G  PHYSIOLOGY. 

Structure   of   the   Small    Intestine. 

Like  the  stomach,  the  intestine  has  four  coats:  (1)  the  external 
serous,  (2)  the  muscular,  (3)  the  submucous,  and  (4)  the  mucous 
coat.  The  serous  coat  is  furnished  by  the  peritoneum.  The  mus- 
cular coat  is  composed  of  two  layers  of  pale,  unstriped  fibers,  the  ex- 
ternal layer  of  longitudinal  fibers,  and  the  internal  layer  of  circular 
fibers.  The  submucous  coat  is  thinner  than  that  in  the  stomach,  but 
is  also  extensible. 

The  mucous  coat  is  thinner  and  redder  than  that  of  the  stomach, 
and,  like  it,  has  a  columnar  epithelium.  It  has  folds  of  mucous  and 
submucous  tissue,  running  in  a  transverse  direction  and  in  the  shape 
of  a  crescent,  which  are  called  the  valvule  conniventes.  These  valv- 
ulse  are  more  abundant  in  the  upper  part  of   the  small   intestine. 


Fig.   20. — Portion   of   the   Wall   of   the   Small   Intestine,   Laid   Open   to 
Show  the  ValvultB  Conniventes.     (Brinton,  Raymond.) 

where  they  overlap  the  edges.  As  you  go  down  the  small  intestine 
you  find  the  numl)er  of  the  valvule  gradually  lessen,  and  in  the  ileum 
they  disappear.  These  folds  are  permanent.  The  minute  elevations 
called  villi  beset  the  mucous  membrane  of  the  small  intestine  and 
even  the  valvulre  conniventes.  They  give  a  velvety  appearance  to 
the  surface  of  the  small  intestine.  In  the  upper  part  of  the  small  in- 
testine the  villi  appear  as  fine  folds,  but  farther  down  the  intestine 
they  appear  as  flattened,  conical  projections.  The  villi  are  V40  inch 
in  height,  and  in  structure  are  appendages  of  the  intestinal  mucous 
membrane. 

Villi.* 

Upon  the  surface  of  the  villi  you  find  an  epithelium  of  regular 
cylindrical  cells.  The  border  cells  of  the  epithelium  of  the  villi  have 
a  broad,  finely  striated  border  which  spreads  over  their  ends  like  a 
cuticle  or  mosaic.     The  other  end  of  the  cell  often  ends  in  a  point 


*  Szymonowics's   Histology   has   been  drawn  upon  in   the   description  of 
the  villi. 


DIGESTION. 


87 


and  is  separated  from  the  underlying  tissues  by  a  thin  basal  mem- 
brane. Each  cell  consists  of  a  granular  protoplasm  containing  an 
oval,  well-defined  nucleus  lying  in  its  lower  half,  in  which  a  distinct 
nucleolus  appears.  The  epithelial  cells  are  joined  together  in 
bridges  of  a  protoplasmic  nature,  with  spaces  between  the  bridges 
filled  with  cement  substance.  In  cholera  and  in  poisoning  by  arsenic 
these  cells  are  shed.  Between  the  epithelial  cells  roundish  structures, 
either  single  or  in  small  groups,  and  of  a  diameter  greater  than  the 
epithelial  cells,  appear.     They  are  quite  transparent,  have  no  true 


Fig.  21. — Blood-vessels   of   an    Intestinal    Villii.g.       (Landois.) 

Un,  Capillaries.     A,   Artery,     CI,   Cylindrical  epithelium.     O,   Surface  of  the 
epithelium.     V,  Vein. 


cell-membrane,  and  only  a  thickened  ectoplasm,  which  undergoes  no 
mucoid  change.  These  cells  are  goblet-shaped,  full  of  protoplasm, 
containing  a  compressed  nucleus.  It  is  generally  considered  that 
these  two  kinds  of  cells,  the  cylindrical  and  the  goblet,  are  separate 
in  origin ;  that  is,  a  young  epithelial  cell  cannot  become  changed  into 
a  goblet  cell.  The  goblet  cells  discharge  mucin,  which  goes  to  form 
the  mucus.  Fasting,  active  digestion,  and  excessive  doses  of  pilo- 
carpin  increase  their  number. 

Going  inward  from  these  cells  we  meet  in  the  villus  a  base- 
ment membrane,  immediately  beneath  it  the  blood-vessels,  then  the 


88  PHYSIOLOGY. 

fibers  of  the  muscularis  mucosa  and  a  single  lacteal  or  lymphatic 
vessel.  The  body  of  the  villus  is  composed  of  adenoid  tissue,  closely 
invested  with  small  and  numerous  bundles  of  smooth  muscular  fibers 
arranged  in  a  longitudinal  and  in  an  oblique  direction,  and  derived 
from  the  muscularis  mucosa.  The  longitudinal  fibers,  when  they 
contract,  shorten  the  villus  and  with  the  valves  in  the  lacteal  empty 
it,  whilst  the  oblique  fibers  keep  the  lacteal  open.  These  muscular 
fibers  are  attached  to  the  sub-epithelial  basal  membrane.  The 
lymph-spaces  in  the  adenoid  tissue  form  a  network  of  channels  com- 
municating with  each  other,  and  contain  leucocytes  and  fine  globules 
of  fat,  which  have  passed  through  the  spaces  between  the  epithelial 


Fig.  22. — Mucous  Membrane  of  the  .Jejunum,  Highly  Magnified, 
(schematic).      (Testut,  Raymond.) 

1,  1,  Intestinal  viUi.     2,  2,  Closed  or  solitary  follicles.     3,  3,  Orifices  of  the 
follicles  of  Lieberkiihn. 

cells  on  the  border,  then  through  the  basal  membrane,  through  the 
lymph-spaces  of  the  parenchyma  of  the  villus,  and  finally  enter  the 
lacteal.  The  lymph-vessels  end  in  the  upper  part  of  the  villus,  in 
a  blind  extremity,  and  show  a  certain  degree  of  anastomosis,  and  when 
joined  form  the  central  chyle-vessel  or  lacteal.  The  lacteal  lies 
in  the  center  of  the  villus,  whilst  the  artery  enters  to  one  side  of  it 
and  spreads  out  into  a  network  of  capillaries,  like  an  umbrella,  over 
the  lacteal  immediately  underneath  the  epithelium  of  the  villus.  The 
number  of  the  villi  has  been  estimated  to  be  about  four  millions. 


DIGESTION.  89 


Glands  of  the  Small   Intestine. 


There  are  four  kinds  of  glands  in  the  mucous  membrane  of  the 
small  intestine.  They  are:  duodenal,  or  Brunner's;  glands  of 
Lieberkuhn ;  solitary ;  and  agminated  glands,   or   Peyer's  patches. 

Brvmner's  glands  are  small,  racemose  glands  situated  in  the  sub- 
mucous tissue  of  the  duodenum.  Toward  the  end  of  the  duodenum 
they  gradually  disajjpear. 

The  glands  of  Lieberkiihn  are  the  most  numerous  of  all  the 
glands  of  the  small  intestine,  and  they  exist  from  the  pyloric  end  to 
the  ileo-c£ecal  valve.  They  are  placed  in  a  vertical  direction  in  the 
thickness  of  the  mucous  membrane  and  open  between  the  villi.  They 
are  about  Vioo  inch  in  length.  They  have  thin  walls  lined  with  a 
columnar  epithelium. 

The  solitary  glands  are  found  in  all  parts  of  the  mucous  mem- 
brane of  the  small  intestine.  They  are  minute,  whitish,  oval  or 
rounded  bodies  scattered  singly  in  the  intestine.  They  are  closed 
vesicles,  and  are  situated  in  the  submucous  tissue.  They  are  lymph- 
nodules  composed  of  retiform  tissue  and  lymphocytes. 

The  agminated  glands  (Peyer's)  are  formed  of  solitary  glands, 
disposed  in  oval  patches.  Usually  there  are  fifteen  to  thirty  of  these 
patches,  from  one-half  to  two  inches  in  length,  and  one-half  inch  in 
breadth.  The  ileum  is  their  usual  habitat,  and  they  are  seated  oppo- 
site the  attachment  of  the  mesentery.  In  the  neighborhood  of  the 
ileo-csecal  valve  they  are  larger  and  more  numerous.  As  the  duo- 
denum is  approached  they  are  smaller  and  fewer.  In  youth  they  are 
distinct,  less  so  in  adult  life,  and  in  old  age  may  disappear.  They  are 
the  seat  of  ulceration  in  typhoid  fever.  The  arteries  of  the  small 
intestine  are  the  superior  mesenteric  and  pyloric.  The  lymphatics 
are  numerous.  The  nerves  are  given  off  by  the  solar  plexus.  Be- 
neath the  mucous  coat  in  the  areolar  tissue  of  the  small  intestine  are 
Meissner's  ganglia.  Between  the  muscular  coats  the  ganglia  of  Auer- 
bach  can  be  found. 

THE  LARGE  INTESTINE. 

This  is  a  cylindrical  tube  differing  from  the  small  intestine  in 
having  a  greater  capacity  and  a  sacculated  appearance.  It  is  about 
five  feet  in  length  and  extends  from  the  ileo-csecal  valve  to  the  anus. 
It  nearly  encircles  the  abdomen  in  its  course.  Like  the  small  intes- 
tine, it  is  divided  into  three  parts:  the  caecum,  colon,  and  rectum. 
The  head  of  the  colon,  the  c»cum,  is  a  wide,  blind  pouch,  or  cul-de- 


90  PHYSIOLOGY. 

sac,,  about  two  and  one-half  inches  in  length  and  breadth.  Toward 
its  bottom  it  curves  inwardly  and  backward  and  is  abruptly  reduced 
to  a  wormlike  prolongation — the  vermiform  appendix.  The  small 
intestine  opens  into  the  csecum,  the  orifice  being  guarded  by  the  ileo- 
ca3cal  valve.  The  second  and  largest  part  of  the  large  intestine  is 
the  colon,  and  it  extends  from  the  caecum  to  the  rectum.  It  consists 
of  four  parts :  the  ascending,  transverse,  and  descending  colon,  with 
the  sigmoid  flexure.  Its  diameter  is  greatest  at  its  commencement, 
being  about  two  and  one-half  inches;  but  it  gradually  lessens  to  an 
inch.  The  sigmoid  flexure  is  shaped  like  the  letter  S.  It  is  the  nar- 
rowest part  of  the  colon.  The  rectum  extends  from  the  sigmoid  flex- 
ure to  the  anus.  It  is  about  seven  inches  in  length.  When  distended 
the  rectum  is  club-shaped,  being  narrow  above  and  expanded  just 
before  it  contracts  to  the  anus.  The  anus  is  completely  surrounded 
by  a  sphincter  muscle. 

Structure  of  the  Large  Intestine. 

The  caecum  and  colon,  like  the  small  intestine,  have  four  coats : 
the  (1)  serous,  (2)  muscular,  (3)  submucous,  and  (4)  mucous.  The 
mucous  membrane  contains  two  kinds  of  glands:  the  glands  of  Lie- 
berkiihn  and  the  solitary  glands.  The  glands  of  Lieberkiihn  are 
closely  set  together  and  give  a  peculiar  sievelike  appearance  to  the 
surface  of  the  mucous  membrane. 

Experiments  upon  the  CECcum  of  the  cadaver  prove  that  the 
action  of  the  ileo-caecal  valve  is  not  dependent  upon  muscular  con- 
traction, for  fluid  forced  through  the  large  intestine  rarely  passes 
into  the  ileum.  When  the  cscum  is  filled  the  dilatation  of  the  same 
presses  upon  the  folds  of  the  valve  so  as  to  press  them  tightly 
together  and  thus  prevent  any  reflux  into  the  small  intestine. 

MOVEMENTS  OF  THE  INTESTINES. 

As  was  the  case  with  the  oesophagus,  the  intestines  are  com- 
posed of  two  muscular  coats :  an  outer  longitudinal  one  and  an  inner 
circular  one.  Movements  in  them  are  caused  by  alternate  contrac- 
tions and  relaxations  of  adjoining  portions  of  the  tube.  To  the 
characteristic  movements  of  the  intestines  two  names  have  been 
given  to  describe  two  separate  forms:  (1)  peristaltic  and  (2)  pendular. 

Peristalsis. — By  this  term  is  implied  the  alternate  contractions 
and  dilatations  of  adjoining  segments  to  produce  a  wavelike  motion 
which  proceeds  from  its  point  of  origin  anywhere  along  the  intestinal 
tract  aivay  from  the  stomach.     "Antiperistalsis"  is  the  term  used  to 


DIGESTION.  91 

designate  the  movements  running  in  an  exactly  opposite  direction: 
that  is,  toward  the  stomach. 

Pendular  Movements. — These  are  the  very  slight  swinging  to- 
and-fro  oscillations,  probably  caused  by  the  contractions  of  the  longi- 
tudinal fibers. 

Cannon  has  shown  that  in  the  cat,  when  fed,  a  portion  of  the 
small  intestine  may  be  seen,  with  its  continuous  contents,  to  sud- 
denly be  divided  into  segments.  These  segments  are  then  also  sub- 
divided. This  segmentation  of  the  intestinal  contents  does  not  move 
the  food  along.  A  peristaltic  wave  does  that.  These  movements  incor- 
porate the  food  with  the  ferments.  When  a  peristaltic  wave  reaches 
the  ileo-colic  sphincter,  it  relaxes  and  permits  the  intestinal  con- 
tents to  pass  into  the  colon.  If  a  reflux  wave  of  the  colon  takes 
place,  it  contracts,  when  the  proximal  part  of  the  colon  is  distended - 
Then  contractions,  an  antiperistaltic  wave,  travel  from  the  point  of 
union  of  the  ascending  and  transverse  colon  tow^ards  the  caecum. 
Then  peristaltic  Avaves  drive  the  contents  into  the  distal  colon. 

In  the  large  intestine,  the  distal  part  of  the  colon  and  its 
adjacent  sigmoid  flexure  are  a  resting  place  for  the  faeces,  and  are 
concerned  in  defecation.  The  chief  point  about  the  distal  colon  is 
its  complete  subordination  to  the  spinal  cord.  The  ileo-colon,  the 
transverse  colon,  and  the  descending  colon  are  a  place  for  the  pro- 
pulsive peristalsis,  as  the  descending  colon  is  never  distended. 

NERVE=SUPPLY  OF  THE  INTESTINES. 

The  small  intestine  receives  fibers  from  the  greater  and  smaller 
splanchnic  nerves,  which  pass  through  the  semilunar  and  superior 
mesenteric  ganglia,  and  then  pass  along  the  mesenteric  arteries  to 
their  destination.  The  right  vagus  also  supplies  the  intestine  with 
fibers. 

The  sympathetic  ganglia  of  Auerbach  lie  between  the  two  mus- 
cular coats  and  extend  from  the  oesophagus  down  throughout  the 
small  and  large  intestine.  Meissner's  ganglia,  also  belonging  to  the 
sympathetic  system,  lie  in  the  submucous  coat.  The  vagi  convey 
motor  impulses  to  the  intestine,  while  the  sympathetics  mainly  con- 
vey inhibitory,  although  they  also  carry  motor,  impulses.  Slight 
stimulation  of  the  splanchnic  ealls  out  motion,  strong  stimulation 
inhibition  of  the  intestinal  movements.  I  have  found  that,  when 
the  right  vagus  is  divided  in  a  rabbit  and  the  cardio-inhibitory  fibers 
are  allowed  to  degenerate  for  five  days,  electric  stimulation  of  the  cut 
vagus  slows  the  pendular  movement. 


92 


PHYSIOLOGY. 


Stimulation  of  any  portion  of  the  intestine  causes  contraction 
above  the  place  of  irritation,  and  inhibition  or  relaxation  below  the 
point  of  irritation.  This  causes  the  food  to  move  onward,  and  is 
due  to  Auerbach's  plexus.  This  is  the  "kw  of  the  intestines,"  accord- 
ing to  Bayliss  and  Starling. 


^m^^ki^-^^^'^''' 


mm 


w'vm:wmMi}BM!ESSmmm 


Fig.  23. — Effect  of  Albumose,  increasing  Peristalsis. 

The  descending  colon  has  its  nerve-supply  from  two  sources: 
(1)  fibers  from  lumbar  nerves  to  sympathetic  chain  and  mesenteric 
ganglia,  and  from  the  mesenteric  ganglia,  by  fibers  running  in  the 
hypogastric  nerves  and  plexus;  (2)  fibers  from  sacral  nerves,  run- 
ning in  the  nervi  erigentes  and  entering  the  pelvic  plexuses,  which 
are  motor  and  antagonize  the  preceding  fibers,  which  are  inhibitory. 
When  the  small  or  large  intestine  is  excised,  it  has  peristaltic  move- 
ments, which  are  due  to  Auerbach's  plexus  acting  as  a  reflex  center. 


DIGESTIOX. 


93 


I  have  found  that  albiimoses  and  peptones  increase  peristalsis.  This 
has  been  confirmed  by  Eoger.  Atropin  increases  the  peristaltic 
movements,  probably  by  an  action  on  the  post-ganglionic  fibers. 
Langley  believes  that  nicotine  and  curare,  in  intestinal  peristalsis, 
act  on  a  substance  intervening  between  the  nerve-ends  and  the 
muscle,  a  mvoneural  substance. 


Fig.  24. — The  Pancreas.     (Posterior  View. 


[  BOURGERY. ) 


1,  Duodenum. 


2,  Duct,  choledicus.     3,  Duct  of  Wirsung.     5,  Union  of  the  two 
ducts.     7,  Accsssory  duct. 


The  distension  of  the  al)domen,  in  many  diseases  of  this  region, 
is  probably  due  to  a  reflex  inhibition  by  the  way  of  the  splanchnic 
nerve,  which  has  power  over  the  tonus  of  the  caliber  of  the  intes- 
tine. 

Salines  are  supposed  to  act  as  aperients  by  their  presence  in  the 
blood,  causing  an  increased  secretion  to  be  poured  out  by  the  blood- 
vessels into  the  intestinal  canal.  The  theory  of  endosmosis  has  been 
abandoned. 


94 


PIIYSIOLOCY. 


PANCREAS. 

The  pancreas  is  a  long  gland,  of  a  reddish-cream  color,  and  is 
situated  behind  the  stomach.  Its  pointlike  extremity  comes  in  con- 
tact with  the  spleen.  It  closely  adheres  to  the  duodenum.  It  is 
about  seven  inches  in  length,  its  width  about  one  and  one-half 
inches,  and  its  thickness  about  one-half  inch.  The  right  and  large 
end  is  the  head;  its  left  free  end  is  its  tail.  The  duct  of  Wirsung, 
or  the  pancreatic  duct,  the  size  of  a  goose-quill,  runs  the  entire 
length  of  the  gland.  Upon  leaving  the  pancreas  the  duct  penetrates 
the  wall  of  the  duodenum,  opening  in  conjunction  with  the  common 
biliary  duct,  about  three  inches  from  the  pylorus. 


7  (> 

Fig.  25. — Schematic  Section  of  Pancreas.      (Vialletox.) 

1,  Origin  of  excretory  canal.  2,  Centro-acinar  cell.  3,  Pancreatic  cell. 
4,  Granular  internal  zone,  zymogen  granules.  5,  External  zone,  clear  part  of 
cell.     6,  Nucleus.    7,  Accessory  nucleus. 

Structure. 

In  structure  the  pancreas  is  an  acino-tubular  gland,  resembling 
the  salivary  glands.  In  fact,  it  has  very  frequently  been  called  the 
abdominal  salivary  gland.  The  lobes  are  composed  of  ducts  which 
have  been  convoluted,  terminating  in  alveoli  or  sacs  and  which  unite 
with  other  tubules  so  as  to  communicate  with  the  main  duct.  The 
small  ducts  are  lined  with  short  columnar  epithelial  cells  which  are 
smaller  than  those  of  the  salivary  glands.  The  secretory  cells  of 
the  pancreas  are  large  and  rounded,  being  distinctive  in  that  they 
possess  an  outer  portion  which  is  nearly  or  quite  homogeneous,  stain- 
ing readily  with  dyes,  and  an  inner  portion,  very  granular,  which 
does  not  stain  easily.  The  latter  forms  about  two-thirds  of  the  cell. 
When   the   gland  is   inactive   the   cells   are   heavily   charged   with 


DIGESTION.  95 

granules  and  the  lumen  is  almost  invisible.  When  active,  the  cells 
first  swell  up  and  press  outward  against  the  basement  membrane; 
later  they  diminish  in  size  as  the  granules  pass  out  through  the  now 
opened  lumen,  and  so  leave  a  large,  clear  zone.  The  presence  of 
these  numerous  small  granules  marks  the  presence,  in  tlie  cells,  of 
a  zymogen,  termed  tnjpsinogen,  which  is  the  precursor  of  trypsin, 
the  active  ferment  of  the  pancreatic  juice.  In  the  interalveolar 
tissue  are  islets  of  small  cells  permeated  with  a  close  network  of 
convoluted  capillaries.  These  cells  are  also  met  with  in  the  carotid 
and  coccygeal  glands.  In  the  pancreas  they  are  called  cells  of  Lan- 
gerhans,  centro-acinar  cells,  and  are  often  degenerated  in  pancreatic 
diabetes. 


A  B 

Fig.  26. — Pancreas  of  Ral)bit  Observed  During  Life.  (KuHJfE  and 
Lea.)  (From  Tigerstedt's  "Human  Physiology-,"  copyright,  1906,  by  D. 
Appleton  and  Company.) 

A,    Resting    glaud.      B,    Secreting    gland. 

The  pancreatic  blood-vessels  are  derived  from  the  splenic  and 
branches  of  the  hepatic  and  superior  mesenteric.  Its  nervous  suppl}'' 
comprises  networks  of  fibers  from  the  splenic  plexus. 

Pancreatic  Secretion  (Pawlow). 

Each  kind  of  food  determines  the  secretion  of  a  definite  quan- 
tity of  pancreatic  juice,  while  the  result  as  regards  ferments  is  truly 
striking.  The  greatest  amount  of  proteid  ferment  is  foun<i  in 
"milk-juice,^'  less  in  "bread-juice"  and  "flesh- juice,'''  The  most 
amylolytic  ferment  occurs  in  "liread-juice,"  less  in  "milk-juice"  and 
"flesh-juice."     On   the  other  hand,   "bread-juice""  is  extraordinarily 


96 


PHYSIOLOGY. 


poor  in  fat-splitting  ferment;  "milk-juiee,"'  on  the  contrary,  is  very 
rich,  "flesh-juice"  taking  an  intermediate  position.  It  is  clear  that 
as  regards  the  two  latter  ferments  the  properties  of  the  juice  corres- 
pond with  the  requirements  of  the  food.  The  starch-holding  diet 
receives  a  juice  rich  in  amylolytic  ferment,  the  fat  a  juice  rich  in 
fat-splitting  ferment. 

The  behavior  of  the  proteid  ferment  may  puzzle  the  student. 
In  the  work  of  the  gastric  glands  we  saw  the  weakest,  here  in  the 
pancreatic  juice  the  strongest,  ferment  poured  out  on  milk.  When, 
however,  we  take  the  quantity  of  juice  into  consideration   we  find  here 


sz 

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hretxcL 

m/lfc.    ; 

J 

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it 

f 

1  '  '* 

Zn 

3  « 

3 

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1 

■ 

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- 

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\ 

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1 

s 

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\ 

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Xr^ 

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2 

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5 

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t    3 

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Fig.  27. — Hourly  Variations  of  the  Pancreatic  Secretion  after  a 
Meal  of  Meat,  Bread,  and  Milk.  (After  a  curve  obtained  in  the  lab- 
oratory of  Pawlow  by  one  of  his  pupils,  A.  Waltheb.  ) 

also  that  administration  of  like  quantities  of  proteid  in  the  form 
of  bread,  flesh,  and  milk  calls  forth  a  secretion  as  regards  the  first 
of  1978,  as  regards  the  second  of  1503,  and  as  regards  the  third  of 
1085  ferment  units ;  that  is  to  say,  vegetable  proteid  likewise  demands 
from  the  pancreas  the  most,  milk  and  milk  proteid  the  least,  ferment. 
The  difference  between  the  stomach  and  the  pancreas  is  limited  to  this : 
that  the  former  pours  out  its  ferment  in  very  concentrated  form 
upon  bread,  the  latter  in  a  very  dilute  condition.  This  fact 
strengthens  the  supposition  that  in  the  digestion  of  bread  a  large 
accumulation  of  hydrochloric  acid  has  to  be  avoided. 


DIGESTION.  97 

When  in  feeding  animals  the  kind  of  food  is  altered  and  the  new 
diet  maintained  for  a  length  of  time,  it  is  found  that  the  ferment- 
content  of  the  juice  becomes  from  day  to  day  more  and  more  adapted 
to  the  requirements  of  the  food.  If,  for  example,  a  dog  has  been  fed 
for  weeks  on  nothing  but  milk  and  bread  and  is  then  put  on  an 
exclusive  flesh  diet,  which  contains  more  proteid,  but  scarcely  any 
carbohydrate,  a  continuous  increase  of  the  proteid  ferment  in  the 
juice  is  to  be  observed.  The  capability  of  digesting  proteid  waxes 
from  day  to  day,  while,  on  the  contrary,  the  amylolytic  power  of  the 
juice  continuously  wanes. 

When  under  the  influence  of  a  given  diet  this  or  that  condition 
of  the  pancreas  had  been  established  in  experiment-animals  in  char- 
acteristic form,  Pawlow  was  al)le,  by  altering  the  feeding,  to  reverse 
it  several  times  in  the  same  animal.  It  seems  then  that  the  gastric 
and  pancreatic  glands  have  what  may  be  called  a  form  of  instinct. 
They  pour  out  their  juice  in  a  manner  which  exactly  corresponds 
both  qualitatively  and  quantitatively  to  the  amount  and  kind  of  food 
partaken  of.  Besides,  they  secrete  precisely  that  quantity  of  fluid 
which  is  most  advantageous  for  the  digestion  of  the  meal. 

Hydrochloric  acid  of  gastric  juice  acts  on  pro-secretin  in  the 
epithelium  of  duodenal  mucous  membrane,  producing  secretin,  a 
hormone^  which,  when  absorbed,  greatly  excites  pancreatic  secretion. 
Fats  in  the  stomach  retard  stomachic  secretion,  but  increase  pan- 
creatic secretion,  chiefly  by  a  reflex  action  through  the  duodenum,  and 
not  from  the  mucous  membrane  of  the  stomach.  Sleep  does  not 
arrest  pancreatic  secretion. 

Psychical  effect,  strong  craving  for  food  and  water,  are  common 
excitants  for  both  gastric  and  pancreatic  secretion.  The  extractives 
of  meat  excite  the  gastric  secretion,  while  acids  and  fats  excite  the 
pancreas. 

Sodium  bicarbonate  and  alkalies  inhibit  pancreatic  secretion. 

Secretory  Nerves  of  Pancreas. 

In  nonnarcotized  dogs  whose  vagus  was  divided  four  days  pre- 
viously and  whose  cardio-inhibitory  fibers  had  lost  their  irritability. 
Pawlow  irritated  the  vagus  without  pain  and  obtained  an  increased 
pancreatic  secretion.  He  found  that  vasoconstriction  of  the  pan- 
creatic vessels  prevented  the  action  of  the  vagus  on  the  pancreas,  as 
did  compression  of  the  aorta  and  pain.     He  also  found  in  the  vagus 


^Hormone  is  derived  from  a  Greek  word,  meaning  to  excite. 

7 


98  PHYSIOLOGY. 

inhibitory  fibers  of  the  secretion,  as  well  as  secretory.  He  believes 
that  secretory  fibers  also  run  in  the  symj^athetic,  not  only  for  the 
pancreas,  but  also  for  the  stomach. 

The  usual  method  of  obtaining  pancreatic  juice  for  experimental 
purposes  is  by  insertion  of  a  cannula  or  by  a  fistula  into  the  duct  of 
Wirsung.  By  this  method  practically  normal  secretion  is  procured, 
whose  composition  is  variable  at  difEerent  times,  depending  upon 
whether  the  fluid  is  collected  three  or  four  hours,  or  two  or  three 
days,  after  the  operation.  The  secretion  examined  shortly  after  the 
operation  is  meager  in  quantity,  though  rich  in  solids;  that  collected 
a  day  or  two  later  is  more  copious,  but  contains  a  smaller  proportion 
of  solid  constituents.  This  is  })robably  due  to  inflammatory  changes 
in  the  pancreas  as  a  result  of  the  operation.  The  pancreatic  juice 
examined  is  usually  obtained  from  dogs,  human  secretions  of  the 
gland  having  been  but  rarely  analyzed,  and  it  has  never  been  obtained 
under  quite  normal  conditions.  Most  experiments  are  performed 
with  the  aid  of  an  artificial  juice  made  by  mixing  a  weak  solution  (1 
per  cent,  sodium  carbonate)  with  a  glycerin  extract  of  pancreas.  It 
is  usual  to  treat  the  pancreas  with  a  dilute  acid  several  hours  previous 
to  its  being  mixed  with  glycerin  to  convert  the  zymogen,  or  mother- 
substance,  trypsinogen,  into  the  ferment,  trypsin. 

Normally,  the  pancreatic  juice  is  colorless,  viscid,  and  gummy; 
it  flows  in  large,  pearl-like  drops,  which  become  foamy  on  agitation. 
The  fluid  is  without  odor,  and  gives  to  the  tongue  an  impression  of  a 
viscid  liquid  and  a  taste  like  that  of  salt.  The  reaction  is  always 
alkaline;  its  specific  gravity  about  1.030. 

In  consequence  of  the  removal  of  a  pancreatic  tumor  Zawadski 
obtained  human  pancreatic  juice  through  the  fistula  remaining,  whx'h 
possessed  powerful  digestive  properties,  and  found  it  to  be  made  up  of 
the  following  composition  in  a  thousand  parts:  135.9  parts  were  of 
solid  nature,  the  remaining  ones  being  water.  Of  the  solid  portions, 
92  were  proteids.  3.4  parts  were  inorganic  in  nature,  while  the  re- 
mainder were  organic  substances  soluble  in  alcohol.  The  figures  rep- 
senting  the  quantities  of  secretion  in  twenty-four  hours  are  very 
various  as  given  by  difl^erent  observers,  but  it  has  been  roughly  esti- 
mated to  average  about  8  ounces. 

The  flow  of  pancreatic  juice  is  somewhat  as  follows :  Before  the 
meal  is  finished  there  begins  the  secretion,  wliich  reaches  its  maximum 
point  at  about  the  third  hour.  After  this  the  secretion  sinks  till  about 
the  sixth  or  seventh  hour,  when  it  increases  to  the  ninth  or  eleventh 
hour,  only  to  sink  gradually  to  the  eighteenth  or  twentieth.     When 


DIGESTION.  99 

the  quantity  is  greatest  the  quality  is  poorest,  and  vice  versa.  Thus 
the  function  of  the  jiancreas  in  man  is  intermittent.  During  secre- 
tion the  ghmcl  is  very  red,  and  its  vessels  dilated,  and  the  venous  blood 
red.  During  repose  the  gland  is  flat  and  of  a  pale-yellow  color,  while 
its  blood-vessels  are  contracted.  The  secretion  is  probably  caused  by 
secretin  and  the  reflex  action  due  to  the  contact  of  the  foods.  The 
pancreatic  secretion  can  be  moderated  or  suppressed  equally  by  reflex 
action,  notably  in  vomiting. 

Of  the  3.4  parts  of  an  inorganic  nature,  the  most  abundant  is 
sodium  chloride,  with  alkaline  and  earthy  phosphates  and  alkaline 
carbonates.  The  alkalinity  of  the  Juice  is  due  principally  to  the 
phosphates  of  sodium.  Pilocarpine  increases  the  secretion,  while 
atropine  diminishes  it. 

The  organic  matters  of  the  pancreatic  juice  comprise  four  prin- 
cipal enzymes  or  ferments.  They  are:  (1)  trypsin,  (2)  amylopsin, 
(3)  steapsin,  and  (4)   a  mill: -curdling  ferment. 

Trypsin,  a  very  important  constituent  of  the  pancreatic  secretion, 
is  much  like  pepsin  of  the  gastric  juice,  in  that  it  is  a  proteolytic 
enzyme  acting  on  the  proteids  and  transforming  them  into  peptones 
through  intermediate  stages.  However,  its  fermentative  powers  are 
much  stronger  and  its  range  of  activity  extends  over  more  space  than 
do  those  of  pepsin.  Atlhough  pepsin  and  trypsin  possess  many  prop- 
erties in  common,  yet  they  are  distinctly  different  and  separate  bodies. 
The  main,  characteristic  difference  is  that  pepsin  requires  an  acid 
medium  for  its  activity,  while  trypsin  acts  and  performs  its  functions 
best  in  an  alkaline  solution  whose  strength  ranges  from  0.5  to  1 
per  cent.  Experiment  has  proved  that  trypsin  can  act  in  a  neutral 
or  very  slightly  acid  medium. 

A  remarkable  feature  of  trypsin  is  the  large  and  rapid  transfor- 
mation of  proteid  matter  of  any  kind  into  peptone.  This  it  produces 
when  in  only  a  moderately  strong  solution.  Thus,  it  is  a  very  capable 
body  to  take  up  the  work  of  proteolysis  where  the  pepsin  of  the 
gastric  juice  left  it.  since  it  is  particularly  a  peptone-forming  ferment. 
As  the  final  products  of  proteolysis,  there  result  peptones.  When 
these  come  into  contact  with  the  pancreatic  juice,  they  are  quickly 
broken  down  into  simple,  crystalline  bodies,  as  leucin.  tyrosin,  aspartic 
acid,  arginin,  and  a  polypeptid. 

Like  pepsin,  the  proteolytic  action  of  trypsin  is  one  of  contact 
also,  only  it  displays  its  powers  more  remarkably  an<l  energetically, 
in  that  it  needs  no  environing  bodies  to  set  it  in  action  other  than 
water,  the  proteid   matters,   and  temperature   equal   to   that   of   the 


100  PHYSIOLOGY. 

body.  Trypsin  displays  no  digestive  ])o\vers  on  nuclein,  keratin,  or 
starches.  There  are  vegetable  trypsins  like  papain  of  Carica  papaya, 
and  bromelin  of  pineapple  juice. 

Hydrochloric  acid  quickly  destroys  trypsin  unless  there  is  great 
excess  of  proteid  substances  present,  which  means  that  the  acid  is  com- 
bined with  them  and  rendered  less  active.  When  a  filled  pancreas-cell 
is  examined,  the  little  granules  within  are  found  not  to  be  active 
trypsin,  but  the  precursor,  or  mother  of  the  ferment.  This  zymogen, 
trypsinogen,  is  readily  converted  into  the  ferment  l\v  the  presence  of 
a  trace  of  acid,  since  a  great  quantity  will  immediately  kill  the  newly 
formed  ferment  as  soon  as  generated. 

Amylopsin, — This  starch-splitting  ferment  converts  starch  partly 
into  dextrin,  but  chiefly  into  isomaltose  and  maltose.  During  the 
first  month  of  life  it  is  thought  that  no  amylopsin  is  formed;  hence 
children  of  that  age  should  not  be  fed  starches.  Amylopsin  difi:ers 
from  ptyalin  in  that  it  can  digest  cellulose,  so  that  it  is  capable  of 
acting  on  unboiled  starch.  In  many  cases  the  failure  of  digestion  of 
the  carbohydrates  by  the  amylopsin  is  associated  with  drowsiness  after 
meals  and  slight  headache. 

The  Steapsin,  or  Fat-splitting  Ferment,  decomposes  the  neutral 
fats  into  fatty  acid  and  glycerin.  It  also  emulsifies  the  fats:  an 
activity  which  is  assisted  by  the  bile.  One  part  of  the  fatty  acids  set 
free  by  the  steapsin  combines  with  alkalies  in  the  intestine  to  form 
soap.  This  soap  favors  the  emulsification  of  the  fats.  Another  part 
of  the  fatty  acid  is  absorbed  as  such  and  combines  with  glycerin  in 
the  intestinal  wall  again  to  form  a  fat.  Kastle  and  Loevenhart  have 
shown  that  lipase  also  has  a  reversible  action :  that  is,  it  can  make  the 
fatty  acids  and  glycerin  reunite  after  they  have  been  separated  by  it. 
The  steapsin  acts  best  in  an  alkaline  medium,  for  acids  stop  it. 
Glycerin  does  not  dissolve  steapsin;  so  that  a  glycerin  extract  is  not 
suitable  for  an  experiment. 

The  Fourth  Ferment  present  in  the  pancreatic  juice  is  an  un- 
named one,  w^iich,  like  rennin,  has  the  power  to  coagulate  milk.  It 
is  hardly  possible  that  its  powers  are  exercised  extensively,  if  at  all, 
since  the  milk  is  probably  coagulated  in  the  stomach  by  the  rennin 
found  there  before  it  ever  reaches  the  duodenum.  The  so-called 
"peptonizing  powders"  are  composed  of  pancreatin  and  sodium  bicar- 
bonate. 

From  the  nature  of  the  resulting  precipitates  in  the  transforma- 
tion of  the  caseinogen  into  casein,  it  is  evident  that  the  two  ferments 
• — rennin  of  the  stomach   and  that   found   in   pancreatic   juice — are 


DIGESTION.  101 

markedly  distinct  and  dare  not  be  confounded.  Eennin  seems  to  re- 
quire the  presence  of  calcium  salts  before  it  can  produce  coagula- 
tion, which,  when  it  does  occur,  presents  the  casein  in  the  form  of  a 
coherent  clot  entangling  in  it  the  fats  present.  There  is  squeezed  out, 
as  it  were,  from  the  closely  formed  curd  a  clear,  yellowish  liquid, 
Icnown  as  the  whey,  containing  some  proteids  with  the  salts  and  sugar 
of  the  milk. 

On  the  other  hand,  experimentation  shows  that  the  ferment  in 
pancreatic  juice  does  not  require  the  presence  of  the  calcium  salts  for 
precipitation  of  caseinogen;  further,  that  the  precipitate  which  does 
occur  is  very  finely  granular  in  nature;  at  the  same  time  the  milk 
seems  to  undergo  no  change  in  its  fluidity,  as  far  as  can  l^e  dis- 
tinguished by  the  naked  eye.  The  presence  of  certain  salts,  which 
entirely  check  the  action  of  rennin,  l)ut  slightly  hinder  the  action  of 
the  pancreatic  ferment.  It  is  Ijelieved  that  this  pancreatic  casein  is 
not  a  true  casein,  for  rennin  placed  in  its  presence  has  the  power  to 
change  it  still  further,  the  resultant  product  being  identical  with 
true  casein. 

Effects  Resulting  Upon  Removal  of  Pancreas. 

It  was  in  1889  that  von  Mering  and  Minkowski  by  experiment 
upon  the  lower  animals  proved  that  removal  of  the  pancreas  was  in 
every  case  followed  by  the  appearance  of  dextrose  in  the  urine,  a  con- 
dition known  as  diabetes,  plus  those  symptoms  marking  the  alisence 
of  pancreatic  secretion  in  the  intestinal  canal  during  digestion.  In 
the  blood  there  was  as  much  as  0.5  per  cent.,  while  in  the  urine  the 
8-per-cent.  mark  was  reached.  These  investigators  found  that  animals 
presented  the  identical  characteristics  as  do  human  beings  suffering 
from  the  same  disease,  namely :  an  abnormal  excretion  of  water  with 
the  appearance  in  the  urine  of  dextrose,  acetone,  and  aceto-acetic  acid. 
Another  step  was  determining  that  this  condition  is  not  due  to  want 
of  the  pancreatic  secretion  in  the  intestine  by  tying  the  duct  of  AYir- 
sung  or  else  plugging  it  and  its  branches  with  paraffin,  but  allowing 
the  organ  to  remain  in  its  proper  position  in  the  l)ody.  The  pres- 
ence of  a  certain  proportion  of  the  whole  gland,  even  though  its  secre- 
tion be  not  allowed  to  reach  the  intestines,  will  prevent  diabetes; 
absence  of  this  diseased  condition  is  still  maintained  though  a  portion 
of  the  gland  be  removed  from  its  normal  position  to  be  transplanted 
elsewhere. 

From  these  data  it  would  seem  that  the  pancreas  possesses  virtues 
in  the  general  economy  other  than  merely  producing  pancreatic  juice. 


102  PHYSIOLOGY. 

Any  disturbance  to  these  functions  is  felt,  not  only  in  the  gland 
itself,  but  throughout  the  entire  body,  since  then  its  metabolism  is 
disturbed.  Thus  is  very  clearly  establislied  one  other  instance  show- 
ing the  intimate  rehition  that  each  and  every  organ  or  part  bears  to 
the  general  mechanism  of  the  entire  body  as  a  unit,  and  the  conse- 
quent general  disturbances  following  its  disease. 

The  transfusion  of  diabetic  blood  into  a  normal  animal  fails  to 
produce  within  the  recipient  any  diabetic  symptoms.  From  this  we 
learn  that  there  was  no  accumulation  in  the  bloocl  of  poisonous  matter 
which  the  pancreas  was  supposed  to  remove.  From  the  facts  noted  it 
is  apparent  that  removal  of  the  pancreas  produces  diabetes,  not  from 
any  influence  upon  surrounding  sympathetic  ganglia  or  hindrance 
to  passage  of  its  secretions  into  the  intestinal  canal,  but  is  caused  by 
the  removal  from  the  system  of  something,  which  something  pos- 
sesses powers  aside  from  those  employed  in  digestion.  The  salivary 
glands,  whose  structure  is  similar  to  that  of  the  pancreas,  when  re- 
moved give  no  untoward  results.  When  the  structures  of  these  two 
glands  are  minutely  and  carefully  examined,  it  is  found  that  there  is 
but  one  difference :  in  the  parenchyma  of  the  pancreas  there  are  pres- 
ent little  cells, — of  Langerhans, — epithelial  in  appearance,  richly 
supplied  with  l)lood-vessels,  but  having  no  connection  with  the  alveoli 
or  ducts  of  the  gland. 

Cohnheim  found  a  body  in  the  pancreas  which  he  calls  the  acti- 
vator, which  resembles  an  internal  secretion  like  adrenalin.  When 
this  activator  is  added  to  muscle-extract,  it  breaks  up  the  sugar  in  the 
blood.  Consequently  the  removal  of  the  pancreas  or  its  activator  lets 
the  sugar  appear  in  the  urine.  Seventy-five  grams  of  muscle  and 
about  .08  gram  of  pancreas  are  the  best  proportions  to  destroy  the 
greatest  amount  of  glucose.  The  pancreatic  activator  is  not  injured 
by  boiling,  and  is  soluble  in  alcohol,  which  facts  show  that  it  is  not 
a  ferment.  It  is  now  believed  that  there  is  some  internal  secretion 
manufactured  by  these  patches  of  Langerhans  cells  in  the  pancreas, 
which  is  a  very  powerful  factor  in  the  disintegration  of  carl^ohydrates, 
but  whose  removal  allows  the  abnormal  production  in  the  blood  and 
urine  of  dextrose.  According  to  several  observers,  the  islets  of 
Langerhans  are  not  independent  structures  of  separate  origin,  but 
are  formed  liy  certain  definite  changes  in  the  arrangements  of  the 
secreting  cells  of  the  pancreatic  tissue.  Secretin  exhausts  the  pan- 
creatic cells,  and  thus  converts  the  greater  part  of  the  secreting  tis- 
sue into  islet  tissue. 

The    embr3'ological    evidence    furnished   by    Laguesse    and    Dale 


DIGESTION.  103 

shows  that  pancreatic  growth  is  a  function  of  the  islet-tissue  cell, 
multiplication  being  ol)served  only  in  the  islet.  As  the  islets  are 
formed  from  the  alveoli,  there  must  be  a  constant  disappearance  of 
islets  and  a  new  formation  of  the  alveoli. 

In  j)ancreatic  diabetes  the  proportion  of  dextrose  to  nitrogen 
(D  :  ]S[)  excreted  in  starvation  is  3  to  1.  In  this  kind  of  diabetes, 
the  sugar  is  derived  from  the  glycogen;  and  when  the  glycogen  is 
used  up,  it,  like  the  nitrogen,  comes  from  the  proteid.  In  ordinary 
states,  after  the  removal  of  the  pancreas  the  sugar  comes  from  the 
dextrose  in  the  food,  and  from  the  proteid  of  the  food  and  of  the 
tissues.  The  cause  of  accumulation  of  sugar  in  hyperglyca3mia  is 
the  removal  from  the  organism  of  some  influence  necessary  to  oxidize 
the  dextrose.     Lsevulose  can  still  be  oxidized  and  also  form  glycogen. 

Continued  Action  of  Trypsin. 

The  proteid  molecule  is  more  thoroughly  broken  up  by  trypsin 
when  it  has  been  previously  acted  upon  by  pepsin,  than  when  attacked 
by  trypsin  alone.  When  the  action  of  trypsin  is  continued  for  a  long 
time,  it  acts  like  an  acid,  hydrolyzing  the  proteid  product  and  form- 
ing mainly  amino-acids,  that  is,  organic  acids  containing  one  or  more 
amido  groups  in  direct  union  with  carbon.  The  amido-acids  are 
chiefly  as  follows: — 

1.  Moxo-AMiNO  Acids. — Glycocoll,  alanin  or  amino-propionic 
acid,  phenyl  alanin,  amino-butyric  acid,  and  leucin,  which  crystallizes 
in  the  form  of  spheroidal  crystals. 

Leucin  (CeH^gKOo)  is  an  a-amido-isobutylacetic  acid,  belonging 
to  the  fatty  acid  series.  It  is  always  formed  in  any  profound  decom- 
position of  proteid,  such  as  boiling  with  dilute  acids,  or  alkalies,  in 
tryptic  digestion,  or  putrefaction.  It  has  been  found  in  nearly  every 
tissue  of  the  body  in  some  proportion,  being  particularly  common  in 
pathological  conditions  of  the  tissues.  It  may  be  produced  syntheti- 
cally in  the  chemical  laboratory. 

(a)  The  mono-amins  of  dibasic  acids: — Aspartic  acid,  gluta- 
minic  acids. 

2.  The  Diamino  Acids. — The  so-called  hexone  bases,  arginin, 
lysin,  histidin. 

Arginin  is  a  product  of  hydrolysis  of  all  proteids.  being  the 
most  abundant  of  the  basic  substances.  It  is  especially  found  in  the 
proteid  of  certain  seeds  and  in  the  protamins.  Salmin,  a  protamin 
of  the  spermatozoa  of  salmon,  contains  80  per  cent,  of  arginin.     This 


104  PIIYSIOLOCY. 

is  changed  into  urea  in  the  liver  hy  a  ferment,  arginase.  Drechsel 
has  estimated  tliat  about  one-ninth  of  the  urea  excreted  could  arise 
from  this  source  alone. 

(a)  Other  diamino  acids: — Diamino-glutaric  acid,  diamino- 
adipic  acid. 

3.  Hydrox-amino  Acids. — Serin,  tyrosin,  found  also  in  elder- 
berries, in  potatoes  and  germinating  cucumbers. 

Tyrosin  (CoHi^NOg)  belongs  to  the  aromatic  group,  and  is 
known  as  oxyphenyl-amido-propionic  acid.  It  is  a  constant  associate 
of  leucin.  It  is  from  tyrosin,  however,  that  cresol  and  phenol  are 
formed. 

4.  A-Pyrrolidincarboxylic  Acid,  or  prolin. 

5.  Caseanic  Acid. — Caseinic  acid. 

6.  Tryptophane  or  Indol-amino-propionic  Acid. — This  crys- 
talline body  gives,  on  distillation,  indol  and  skatol.  When  the  amido 
bodies  are  formed  from  the  proteid  molecule  by  the  trypsin,  a  nucleus 
of  the  proteid  molecule  remains,  which  is  a  polypeptid. 

7.  The  Sulphur  Bodies. — Albumin,  when  treated  with  lead 
salts  in  the  presence  of  caustic  alkali,  yields  a  black  coloration,  indi- 
cating the  presence  of  sulphur  in  the  molecule.  One  of  these  bodies 
is  cystin. 

8.  The  Carbohydrate  Group. — There  are  certain  proteids, 
amongst  which  are  mucins  and  cartilage,  which  readily  yield 
a  carbohydrate  group  on  hydrolysis.  Serum-albumin  and  egg-albu- 
min contain  a  carbohydrate  group  which  forms  no  small  part  of  the 
whole  molecule  of  albumin.  Thus  egg-albumin  contains  glycosamin — 
this  last  fact  is  important  in  the  consideration  of  diabetes ;  the  sugar 
comes  from  the  proteid. 

Gl3'cosamin  injected  into  the  circulation  is  in  great  part  elimi- 
nated as  such.  Proteids  containing  glycosamin  are  completely  oxi- 
dized.    One-twelfth  of  egg-albumin  is  glycosamin. 

It  has  been  shown  by  Giselt  that  alcohol,  when  given  either  by 
the  stomach  or  rectum,  increases  the  secretion  of  the  pancreatic  Juice 
by  an  action  through  the  vagi.  The  vagi  contain  the  secretory  nerves 
of  the  pancreas.  However,  alcohol  reduces  the  digestive  activity  of 
the  trypsin,  the  amylopsin,  and  the  steapsin. 

I  have  found  that  an  infusion  of  the  pancreas,  when  injected  per 
jugular,  decreases  the  pulse  and  the  arterial  tension;  afterward  the 
tension  rises. 


DIGESTION. 


105 


LIVER. 

The  largest  gland  in  the  body  is  the  liver.  Its  shape  is  that  of 
a  triangular  prism  or  ovoidal,  with  its  long  diameter  transverse.  Its 
convex  surface  is  against  the  diaphragm.  Its  concave  surface  is  in 
contact  with  the  stomach,  colon,  and  right  kidney.  The  right  and  left 
lateral  ligaments,  with  the  suspensory  ligament,  hold  it  in  position. 
It  weighs  from  three  to  four  pounds.  The  right  portion  of  the  liver 
is  much  larger  than  the  left.  It  is  also  thicker  and  extends  lower  in 
the  abdomen  and  higher  in   the  thorax.     It  is  of  a  firm  structure. 


13  H, 


1,  Left  lobe.  2,  Right  lobe.  6,  Lobus  quadratus.  7,  Lobus  Spigelii.  9,  Gall- 
bladder. 10,  Cystic  duct.  11,  Hepatic  duct.  12,  Common  biliary  duct.  13,  Portal 
vein.     14,   15,    Hepatic   veins.     16,    Inferior  vena  cava.     19,    Hepatic  artery. 


smooth  on  the  surface,  and  of  a  reddish-brown  color.  The  liver  has 
five  lobes,  five  fissures,  five  ligaments,  and  five  vessels.  The  chief 
fissure  to  remember  is  the  transverse  fissure,  which  is  the  point  where 
the  blood-vessels  and  nerves  enter  the  liver  and  where  the  lymphatics 
and  excretory  duct  emerge.  The  lobes  are  the  quadrate,  caudate,  right 
and  left,  and  lobus  Spigelii.  the  most  important  being  the  right  and 
left.  The  vessels  are  the  hepatic  artery,  vein,  and  duct,  the  portal 
vein,  and  lymphatics.     The  nerves  are  derived  from  the  solar  plexus 


106  PHYSIOLOGY. 

and  the  left  vagus  lias  some  (ihcrs  <;()ing  to  it.  The  wliole  organ  is 
insheatlied  in  a  very  line  coat  of  areolar  tissue  known  as  Olisson's 
capsule. 

Structure. 

The  hepatic  substance  is  readily  torn  and  has  a  granular  appear- 
ance; these  coarse  granules,  corresponding  with  the  distinct  spots 
seen  on  the  surface,  are  polyhedral,  and  are  the  lobules  of  the  liver. 
These  lobules  are  V12  ii^ch  in  diameter.  In  stud}dng  the  relation  of 
these  lobules  to  the  blood-vessels  and  duets  of  the  liver,  it  is  found 
that  an  extreme  branch  of  the  hepatic  vein  commences  in  the  axis 
of  every  lobule  and  emerges  at  its  base  to  join  a  larger  branch.  This 
connection  of  veins  and  lobules  reminds  one  of  the  attachment  of  the 
leaves  by  their  midribs  and  stems  to  the  branches  of  trees. 

The  capsule  of  Glisson  divides  the  liver-substance  into  these 
lobules,  for  the  areolar  tissue  enters  the  transverse  fissure  of  the  liver. 

Microscopically,  each  lobule  is  made  up  of  epithelial  cells,  natur- 
ally spheroidal,  but  because  of  compression  are  more  or  less  polygonal. 
These,  the  true  liver-cells,  are  about  ^/^ooo  i^ch  in  diameter,  contain- 
ing protoplasm  with  large,  round  nuclei  which  have  one  or  more 
nucleoli.  The  cells  are  held  together  by  an  albuminous  cement-sul)- 
stance ;  in  it  are  fine  channels  containing  the  bile-capillaries. 

The  portal  vein  also  has  its  course  in  the  portal  canals,  where  it 
divides  and  subdivides.  By  its  division  between  the  lobules  in  the 
interlobular  connective  tissue  it  forms  the  interlobular  vein.  From 
this  vein  fine  capillary  branches  are  given  off,  which  pierce  the  envelop- 
ing membrane  of  the  lobule  to  find  their  way  toward  its  center  in  a 
converging  manner.  In  their  course  to  its  center  they  pass  in  close 
proximity  to  the  hepatic  cells,  and  it  is  here  that  the  real  secretion  of 
the  bile  takes  place.  From  the  point  of  union  of  the  capillaries  in 
the  center  of  the  lobule  there  proceeds  a  single,  straight  vein,  called  the 
intralobular  vein.  Arrived  at  the  base  of  the  lobule,  this  vein  empties 
its  contents  into  the  sublobular  vein,  a  radicle  of  the  hepatic  vein, 
which  empties  into  the  inferior  vena  cava. 

The  hepatic  artery  does  not  furnish  the  l)lood  for  the  secretion  of 
bile.  Its  function  is  to  furnish  a  blood-supply  to  Glisson's  capsule 
and  to  the  investment  of  the  lobules  and  the  walls  of  the  bile-ducts. 

The  course  of  the  bile-duds  is  very  similar  to  that  of  the  portal 
vein  and  hepatic  artery.  Bile  capillaries  have  no  distinct  walls  of 
their  own  except  those  formed  by  the  liver-cells  between  which  they 
are  situated.     All  cells,  except  those  in  contact  with  capillary  blood- 


DIGESTION. 


107 


vessels,  are  completely  girded  with  bile-capillaries.  Intracellular 
passages  pass  from  the  bile-capillaries  into  the  interior  of  the  liver- 
cells.  After  nmnerous  anastomoses,  the  bile-ducts  form  larger  ones, 
to  leave  the  liver  through  the  hepatic  fissure  as  two  main  branches. 
Toward  the  exit  the  bile-ducts  become  correspondingly  larger,  with 


Fig.  29. — Diagi'aminatic  Representation  of  an  Hepatic 
Lobule.      (Landois.) 

I.  Vi,  Ti,  Interlobular  veins.  Tc,  Central  vein,  c,  Capillcry  between  the  two. 
Vs,  Sublobular  vein.  Vt\  Vascular  vein.  A,  A,  Branches  of  the  hepatic  artery, 
approaching  the  capsule  of  Glisson  and  the  larger  blood-vessels  at  r,  r,  and 
forming  the  vascular  vein  further  on,  entering  the  capillaries  of  the  interlobular 
veins  at  i,  i.  y.  Branches  of  the  bile-duct,  dividing  at  J",  x,  between  the  liver- 
cells,  d,  d.  Situation  of  liver-cells  in  the  capillary  network.  II.  Isolated  liver- 
cells,  at  c  lying  upon  a  capillary  blood-vessel  and  forming  a  fine  bile-duct  at  a. 


increase  in  the  thickness  of  their  walls.  These  are  found  to  contain 
fibrous  tissue  with  bundles  of  nonstriped  muscle-fibers  plus  small 
mucus-secreting  glands.  Within  each  lobule  are  three  networks:  a 
network  of  blood-capillaries,  a  network  of  liver-cells,  and  a  network 
of  bile-capillaries. 


108  PHYSIOLOGY. 

The  Gan=bladder. 

The  gall-bladder  acts  as  the  natural  reservoir  for  storage  v  i  the 
bile.  It  is  a  pear-shaped  bag  of  a  musculo-membranous  texture, 
capable  of  containing  rather  more  than  a  fluidounce,  and  is  situated 
upon  the  under  side  of  the  liver  in  a  fissure  fashioned  for  it.  It  is 
about  four  inches  long,  one  inch  at  its  fundus,  or  base. 

The  structure  of  the  gall-bladder  consists  of  three  coats:  an 
outer,  serous  coat;  a  middle,  fibrous;  and  an  inner,  mucous  coat. 
The  fibrous  coat  contains  both  circular  and  longitudinal  fibers.  The 
inner  surface  of  the  bladder  is  lined  with  mucous  membrane,  which  is 
of  a  yellowish-brown  color. 

The  hepatic  duct,  formed  by  union  of  two  bile-ducts  issuing  from 
the  liver,  is  about  one  and  one-half  inches  long.  By  its  joining  the 
cystic,  also  about  one  and  one-half  inches  in  length,  is  formed  the 
common  bile-duct,  known  as  the  ductus  communis  choJedochus.  This, 
the  largest  of  the  three,  is  three  inches  long,  with  the  diameter  of  a 
goose-quill,  emptying  with  the  pancreatic  duct  into  the  duodenum 
through  a  common  opening. 

Functions  of  the  Liver. 

The  liver,  being  such  an  important  gland,  naturally  occupies  a 
very  prominent  position  in  the  general  metabolism  of  the  economy. 
Its  principal  functions  are:  the  formation  of  an  internal  secretion, 
glycogen;  the  formation  of  urea ;  and.  last,  the  production  of  the 
bile,  in  which  as  a  vehicle  many  poisonous  products  within  the  body 
are  expelled. 

Bile  is  a  thick,  golden-colored  liquid  of  a  very  bitter  taste.  Its 
secretion  by  the  liver  represents  only  one  subsidiary  function  of  the 
many  performed  by  this  important  gland.  It  represents  waste  al- 
buminous matters,  together  with  coloring  pigments  and  mineral  salts 
dissolved  in  water.  Though  primarily  excrementitious  substance  and 
performing  the  necessary  functions  of  such,  it,  however,  possesses  some 
powers  to  aid  intestinal  digestion,  both  directly  and  indirectly. 
These  will  be  discussed  under  the  head  of  the  "Uses  of  Bile." 

The  secretion  of  bile  is  a  continuous  process,  for  a  supply,  though 
scanty,  is  constantly  passing  into  the  duodenum.  The  arrival  of 
chyme  in  the  duodenum  immediately  calls  for  an  increased  amount, 
to  be  followed  by  a  second  increase  some  hours  later. 

Starling  holds  that  the  mechanism  by  which  the  increased  secre- 
tion of  bile  is  produced  at  the  time  when  this  fluid  is  required  in 


DIGESTION.  109 

the  intestine,  is  identical  with  that  for  the  secretion  of  pancreatic 
juice,  and  that  in  each  case  secretin — formed  by. the  action  of  hydro- 
chloric acid  on  the  duodenal  epithelium — is  absorbed,  and  excites  the 
liver  and  pancreas  to  increased  activity. 

Barbera  has  shown  that  a  meat-diet  excites  the  greatest  secretion 
of  bile,  fat  less,  and  a  carbohydrate  diet  hardly  any. 

It  is  in  the  intermission  between  meals  that  the  liver  is  least 
active,  and  it  is  then  that  only  a  small  supply  reaches  the  duodenum. 
It  continues  during  pains  the  most  violent,  in  intestinal  congestion, 
and  in  peritoneal  inflammations. 

Contrary  to  the  plan  of  all  the  other  secreting  and  excreting 
organs,  the  main  supply  of  blood  to  the  liver,  and  from  which  its  secre- 
tion, the  bile,  is  formed,  is  venous:  from  the  portal  vein.  The  nutrient 
function  of  the  hepatic  artery  is  to  supply  structures  and  membranes 
only.  Since  the  portal  vein  furnishes  the  supply,  the  bile  is  secreted 
at  a  very  much  lower  pressure  and  therefore  more  slowly  than  those 
secretions  from  glands  whose  supply  is  arterial,  as  the  pancreas  and 
salivary  glands.  It  is  quite  natural  that  a  fluid  so  complex  as  the 
bile  demands  for  its  preparation  a  much  longer  period  of  time  than 
one  which  contains  only  water,  salts,  and  certain  principles  of  the 
blood.  Though  not  directly  governed  by  nerve-influences  upon  the 
portal  vein,  the  blood-supply  to  the  liver  is  varied. 

Compared  with  the  size  of  the  liver,  the  secretion  is  small  and 
slow,  and  holds  but  little  relation  to  the  mass  of  blood  traversing  it. 
The  quantity  secreted  per  diem  has  been  variously  computed  at  two 
pounds.  Its  specific  gravity  in  man  averages  1.026;  reaction,  neutral 
or  slightly  alkaline. 

Chemical   Properties  and   Constituents  of  the   Bile. 

Bile  mixes  with  water,  producing  no  turbidity ;  heat  produces  no 
coagulation  because  of  the  absence  of  any  coagulable  proteids.  Alco- 
hol precipitates  mucin,  diastase,  and  bilirubin,  if  the  latter  is  present. 
Acetic  acid  precipitates  mucus ;  lead  acetates,  the  biliary  salts.  When 
in  contact,  bile  rapidly  destroys  the  red  blood-corpuscles. 

Bile  contains  both  organic  and  inorganic  materials.  Those  or- 
ganic are  mucin,  biliary  pigments,  biliary  salts,  cholesterin.  lecithin, 
neutral  fats,  soap,  urea,  and  diastase.  In  organic  matters  are  water, 
chloride  of  sodium,  and  phosphates  of  iron,  calcium,  and  magnesium. 

The  means  by  which  the  various  components  of  the  bile  are 
formed  is  as  yet  not  thoroughly  understood.  Some  of  its  constituents 
may  exist  in  the  portal  blood;  thus  the  pigment  is  produced  by  the 


110 


PHYSIOLOGY. 


decomposition  of  the  blood.  If  haemoglobin  itscslf  or  substances  which 
are  capable  of  separating  tlie  coloring  matter  from  the  red  corpuscles 
be  injected  into  the  portal  blood,  there  is  a  proportionate  increase  in 
bile-])igment.  Biliary  acids  are  not  preformed  in  the  blood,  for  upon 
extirpation  of  the  liver  there  follows  no  appearance  of  them  in  the 
blood.  Evidently  the  hepatic  cells  must  exert  some  functions  as  yet 
not  understood. 

The  composition  of  human  bile  is  approximately  as  follows : — 


Water 982 

f  Mucin  and  {)igments   1.5 

Bile-salts    7.5 

Solids    J    Lecithin  and  soaps    LO     (-18 

Cholesterin    0.5 

I   Inorganic  salts  7.5 


^  parts  in  1000. 


Fig.  30. — Glycocholic  Acid.      (Duval.) 


Bile=mucin. 

The  latest  investigations  show  that  human  bile  contains  real 
mucin. 

Bile^salts. 

There  are  two  salts  of  bile,  both  having  sodium  as  a  base.  These 
are  glycocholate  and  taurocholate.  These  two  acids  are  very  closely 
related  to  each  other,  for,  on  boiling  with  stronger  acids,  a  common 
nonnitrogenous  body  is  obtained  called  cholalic  acid,  and  an  amido- 
acid  which  contains  nitrogen.  The  gl^-cocholic  acid  gives  glycin  and 
the  taurocholic  acid  gives  taurin,  which  contains  sulphur.  Taurin, 
from  its  sulphur-content,  must  be  a  result  of  the  metabolism  of  the 
proteids,  and,  according  to  Friedmann,  it  comes  from  cystin.     Hence 


DIGESTION. 


Ill 


the  bile-acids  represent  the  final  changes  of  the  proteids  of  the  livcr- 
cell.  In  man  these  acids  exist  in  variable  proportions.  The  bac- 
teria of  the  intestinal  canal  break  up  the  bile-salts. 

Glycocholic  acid  is  a  monobasic  acid,  crystallizing  in  long,  fine 
needles.  Taurocholic  is  also  monobasic;  it  cr3'stallizes  with  great 
difficulty,  forming  fine,  deliquescent  needles,  which  in  solution  have 
a  bitter-sweet  taste.     Proteid  is  the  source  of  glycin  and  taurin. 

Subcutaneous  and  venous  injections  of  bile-salts  cause  coma  and 
depression. 

Hay's  Sulphur  Test  for  Bile-salts. — On  the  surface  of  bile  or  a 
solution  holding  bile-salts,  sprinkle  flowers  of  sulphur;  it  will  sink 
to  the  bottom  of  the  tube,  while  on  most  other  liquids  it  will  float. 

The  bile-salts  lower  the  surface  tension  of  fluids  in  which  they 
are  dissolved. 


Fig.  31.— Taarin.      (Duval.) 

Pettenkofer's  Test  for  Bile-acids. — To  a  nearly  equal  volume  of 
bile  add  a  drop  or  two  of  syrup  of  cane-sugar  (10  per  cent.). 
Pour  concentrated  H^SO^  at  the  line  of  junction  of  the  two 
fluids,  then  a  purple  color  is  obtained.  The  purple  color  pro- 
duced shows  absorption  bands  in  the  spectrum.  The  acid  on  the 
cane-sugar  produces  a  body  called  furfuraldehyde,  which  sets  up  a 
reaction  with  the  cholalic  acid  to  produce  the  color. 


The  Bile=pigments. 

Normally,  the  color  of  the  l)ile  is  due  to  the  presence  of  but  two 
bile-pigments:  hilinibin  and  biliverdin.  When  pathological,  other 
characteristic  ones  have  been  described.     Depending  upon  the  propor- 


112  PHYSIOLOGY. 

tion  of  each  present,  the  color  may  range  from  reddish-brown  to 
grass-green.  They  are  formed  from  the  haemoglobin  of  the  blood — 
the  mother  of  all  the  bile-pigments.  In  man  and  carnivora  bilirubin 
predominates  and  gives  to  the  bile  its  yellow  color;  the  green  color 
of  that  of  herbivora  is  due  to  biliverdin. 

Bile  contains  neither  bilirubin  nor  biliverdin  free,  but  combi- 
nations of  these  two  substances  as  salts :  bilirubinates  and  biliverdin- 
ates  of  the  alkalies.  The  bilirul)inates  are  transformed  into  biliver- 
dinates  by  the  oxygen  of  the  air.  These  bodies,  bilirubin  and  bili- 
verdin, act  as  acids. 

Bilirubin,  isomeric  with  haematoporphyrin,  represents  the  iron- 
free  pigment  of  the  bile;  its  formula  is  CigH^gl^aC);!-  This  is  the 
permanent  pigment  of  the  bile  and  may  also  appear  as  a  calcium  com- 
pound in  red  gall-stones.  When  exposed  to  the  air  and  in  an  alkaline 
solution,  it  oxidizes  very  readily,  changing  into  biliverdin;  because 
of  this,  bile,  when  standing,  assumes  a  greenish  tint. 

Biliverdin  is  present  in  all  biles  of  a  greenish  color.  It  occurs 
as  such  in  the  liver-secretion  of  herbivora,  but  may  be  obtained  by 
allowing  human  and  carnivorous  bile  to  oxidize  slowly  by  exposure  to 
the  air.  Its  formula  is  Ci6lI^8No04,  having  one  more  atom  of  oxy- 
gen than  bilirubin. 

When  bilirubin  arrives  in  the  intestine  the  bacteria  generate 
nascent  hydrogen,  which  reduces  it  and  generates  another  pigment, 
the  coloring  matter  of  the  faeces,  called  stercobilin.  This  stercobilin 
when  absorbed  and  excreted  in  the  urine  is  called  urobilin. 

Gmelin's  Test  for  Bile-pigments. — Add  to  some  bile  some  nitric 
acid  containing  nitrous  acid,  when  there  will  be  a  play  of  colors: 
green,  blue,  purple,  and  yellow.  These  tints  are  due  to  the  oxidation 
of  bile-pigments.  The  green  is  biliverdin ;  the  blue,  bilicyanin ;  the 
purple,  bilipurpurin ;  and  the  yellow,  choletolin. 

Cholesterin. 

Cholesterin  is  a  monovalent  alcohol.  It  is  present  to  some  ex- 
tent in  all  protoplasmic  structures, — blood-corpuscles. — but  particu- 
larly in  bile  and  nervous  tissues.  In  the  latter  it  forms  a  very  im- 
portant part  of  myelin.  In  the  l:)ile  it  forms  but  a  small  proportion 
of  its  contents — from  1  to  5  per  cent.  It  is  insoluble  in  water  and 
dilute  saline  solutions,  but  readily  soluble  in  ether,  chloroform,  alco- 
hol, etc.;  in  this  respect  it  resembles  fat,  though  not  a  true  fat.  In 
bile  it  is  readily  dissolved,  because  of  the  presence  of  bile-salts.  If, 
for  any  reason,  the  latter  should  be  insufficient,  the  cholesterin  passes 


DIGESTION. 


113 


out  of  solution  to  form  concretions  around  any  foreign  particles  or 
previously  hardened  concretions,  forming  a  gall-stone  in  man. 
Another  kind  of  gall-stone  is  bilirubinate  of  calcium,  rare  in  man, 
but  frequent  in  the  ox.  Besides  its  characteristic  crystals,  cholesterin 
is  also  detected  by  various  color-reactions  in  the  presence  of  iodine  and 
sulphuric  acid. 

The  general  presence  of  cholesterin  in  so  many  parts  and  cells 
of  the  body  leads  to  the  impression  that  it  is  a  cleavage  product  of 
metabolism,  being  one  of  the  waste-elements  in  the  life  of  the  cell, 
especially  the  nerve-cell.  Being  absorbed  by  the  blood,  it  finds  its  way 
to  the  liver,  there  to  be  elaborated  and  to  appear  in  the  bile.  Being  an 
excrement,  it  is  not  reabsorbed,  but  is  expelled  from  the  economy  as  a 
part  of  the  faces.     Pathological  changes  in  tissues  are  always  marked 


Fig.  32. — Crystals  of  Cholesterin.      (Duval.) 


by  an  increased  quantity,  which  may  be  accounted  for  by  loss  of 
vitality  in  the  diseased  cells  so  that  they  are  unable  to  break  down 
the  cholesterin. 

Cholesterin  is  not  poisonous  to  animals. 

Lecithin  is  found  chiefly  in  nervous  tissues,  red  corpuscles,  and 
the  bile.  It  is  most  abundant  in  the  nervous  system.  This  is  a  com- 
pound of  a  nitrogen  base,  cholin,  with  glycero-phosphoric  acid  with 
fatty  acid  radical.  Combined  with  a  carbohydrate  residue,  it  is 
found  in  the  liver,  and  is  then  called  jecorin. 

When  lecithin  is  taken  by  the  mouth  it  is  broken  up  in  the 
intestine  into  cholin,  a  poisonous  alkaloid ;  but  the  intestinal  bacteria 
destroy  it  at  once,  producing  methane,  carbonic  acid,  and  ammonia. 


114 


PHYSIOLOGY. 


Uses  of  Bile. 

In  fasting,  not  a  drop  of  bile  enters  the  intestine.  Fat,  meat 
extractives,  and  the  products  of  digestion  of  egg-albumin  set  up  a 
free  discharge  of  the  fluid.  Bile  accentuates  the  activity  of  the 
pancreatic  enzymes,  especially  the  fat-splitting  ones,  the  action  of 
which  is  increased  twofold.  The  pancreatic -secretion,  in  its  hourly 
rate,  corresponds  closely  with  the  entry  of  bile  into  the  intestine  under 
the  same  conditions  of  diet.     The  similarity  is  most  striking.     Bile 


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Fig.  33. — Curves  Showing  the  Velocity  of  Secretion  of  Bile  into  the 
Duodenum  on  ( 1 )  a  diet  of  milk,  uppermost  curve ;  ( 2 )  a  diet  of  meat, 
middle  curve;  (3)  a  diet  of  bread,  lowest  curve.  The  divisions  on  the 
abscissa  represent  intervals  of  thirty  minutes;  the  figures  on  the  ordi- 
nates  represent  the  volume  of  secretion  in  cubic  centimeters.  (Howell, 
after  Bruns.) 

arrests  the  action  of  pepsin,  which  is  injurious  to  the  ferments  of  the 
pancreatic  juice,  and  favors  the  ferments  of  the  latter,  especially  the 
fat-splitting  one. 

Bile  is  principally  excremcntitious.  It  partly  emulsifies  the  fats 
and  contributes  to  their  solution  by  the  soap  which  the  alkalies  of  the 
bile  produce.  The  emulsification  of  fat  is  a  mechanical  preparation 
of  it,  in  order  that  lipase  may  act  upon  it.     By  thus  rendering  the 


DIGESTION.  1 15 

fats  alkaline  in  part  they  are  able  to  come  in  closer  touch  with  the 
intestinal  mucous  membrane,  and  to  be  absorbed  by  it.  Endosmotic 
experiments  have  proved  that  the  fats  are  imbibed  and  that  they 
traverse  more  easily  membranes  that  are  impregnated  with  an  alkaline 
solution  than  those  simply  wet  with  water.  Experimentally,  when  the 
bile  is  turned  out  of  its  course,  the  chyliferous  vessels  are  not  filled 
with  white,  milky  fluid,  since  only  one-seventh  of  the  normal  amount 
of  chyle  is  absorbed. 

As  an  excrementitious  substance,  the  bile  may  serve  as  a  medium 
for  the  separation  of  the  excess  of  carbon  and  hydrogen  from  the  blood, 
particularly  during  intra-uterine  life. 

When  the  chyme  passes  into  the  duodenum,  the  glycocholate  and 
taurocholate  of  sodium  are  broken  up  by, the  acid  in  the  chyme  to  form 
sodium  chloride,  at  the  same  time  setting  the  bile  acids  free.  Imme- 
diately they  are  precipitated,  carrying  down  with  them  the  pepsin, 
making  the  chyme  alkaline  and  more  turbid,  due  to  the  precipitation 
of  the  unpeptonized  proteids.  This  thickening  of  the  stomach  con- 
tents aids  very  materially  in  slowing  the  movements  of  the  digested 
products  through  the  intestines,  thus  giving  the  villi  and  blood-vessels 
more  ample  time  to  absorb  nutritious  substances. 

By  rendering  the  chyme  alkaline,  it  aids  the  action  of  the  pan- 
creatic juice,  which  is  most  ejffective  as  a  digestive  agent  in  an  alkaline 
medium,  at  the  same  time  favoring  absorption,  since  alkaline  liquids 
permit  of  more  ready  osmosis. 

To  the  bile  has  been  given  the  credit  of  being  a  natural  antiseptic, 
in  that  it  hinders  putrefaction  in  the  intestine.  The  bile  itself  easily 
becomes  putrid  on  standing.  How  can  it  prevent  the  putrescence, 
then,  of  the  intestinal  contents?  That  it  does  in  some  way  diminish 
this  degenerative  jorocess  is  very  evident,  for,  when  the  common 
biliary  canal  is  ligated,  the  faeces  are  more  foetid  and  the  intestinal 
gases  more  abundant.  The  bile's  so-called  antiseptic  powers  must  be 
accounted  for  by  its  hastening  absorption  and  assisting  it  to  such  an 
extent  that  the  quantity  of  matter  capable  of  putrefaction  is  greatly 
diminished  in  quantity. 

It  has  been  found  that  bile  stimulates  muscles  when  in  contact 
with  them.,  throwing  them  into  a  violent  state  of  tetanus,  while  at 
the  same  time  it  irritates  the  nerves.  By  this  action  the  economy 
possesses  a  natural  purgative.  By  it,  as  a  stimulus,  the  secretion  of 
the  glands  of  the  intestinal  mucous  membrane  is  increased,  and  more 
rapid  peristaltic  movements  of  the  intestinal  muscles  induced  to  aid 
in  the  propulsion  of  their  contents. 


116  PHYSIOLOGY. 

Reabsorption  of  Bile=salts. 

When  it  was  ascertained  that  the  bile-salts  were  the  products  of 
the  hepatic  cells,  that  only  a  small  proportion  appeared  in  the  faeces, 
with  a  still  smaller  proportion  in  the  urine,  the  question  arose:  Is 
.the  remainder  reabsorbed  by  the  intestines  to  be  again  secreted  from 
the  blood  by  the  hepatic  cells? 

Bile-salts  taken  by  the  mouth  produce  an  increased  flow  of  the 
bile,  which  is  at  the  same  time  higher  in  its  percentage  of  proteids. 
Dog's  bile,  containing  normally  only  taurocholate  of  sodium,  has  been 
found  to  contain  glycocholate,  when  that  salt  had  been  injected  into 
the  animal's  blood.  Again,  when  bile  has  been  taken  from  an  animal 
for  some  time  by  a  fistula,  its  quantity  of  solids  diminishes,  showing 
that  the  hepatic  cells  cannot  give  back  these  salts  to  it  when  the  portal 
blood  does  not  convey  to  them  the  materials  for  their  formation. 
From  these  and  other  facts  it  was  deduced  that  there  must  exist  in  the 
body  reabsorption  of  bile-salts. 

Antitoxic  Function  of  the  Liver. — It  was  found  that  nicotine 
added  to  the  portal  blood  of  an  experimental  circulation  through  the 
liver  soon  vanishes.  Similar  experiments  with  strychnine,  morphine, 
and  quinine  resulted  in  the  same  way.  These  alkaloids  are  not  only 
deposited  in  the  liver-cells,  but  they  experience  a  change  in  their 
chemical  constitution  by  which  they  lose  their  poisonous  properties. 
It  is  well  known  that  the  liver  is  a  storage  for  the  metallic  poisons 
mercury,  arsenic,  iodine,  and  antimony  for  long  periods.  The  liver 
also  transforms  the  bodies  developed  by  action  of  intestinal  bacteria  on 
proteid.  I  refer  to  indol  and  phenol.  Here  the  liver  exerts  a  protec- 
tive action  against  poisoning  by  these  bodies. 

When  the  liver  is  removed,  certain  nervous  symptoms  supervene, 

such  as  somnolence,  ataxia,  convulsions,  and  coma.     This  is  supposed 

to  be  due  to  the  ammonia  salts,  generated  in  proteid  digestion,  get- 

•  ting  into  the  blood.     When  the  liver  is  present,  they  are  converted 

into  urea. 

The  liver  also  reduces  the  toxic  activity  of  poisons  generated 
by  specific  bacteria,  as  by  the  typhoid  bacilli  and  tetanus  organisms. 
The  liver  is  probably  the  seat  of  most  active  oxidations,  and  it  is  by 
these  chemical  activities  that  it  acts  as  a  protective  agent  against 
poisons. 

Internal  Secretion  of  the  Liver  (Glycogen). — Besides  secreting 
the  bile  to  be  partly  used  in  digestion,  but  mainly  as  an  excrementi- 
tious  substance,  the  liver  possesses  still  another  remarkable  function, 


DIGESTION.  117 

namely:  separation  from  the  portal  blood  by  its  cells  of  a  substance 
known  as  glycogen,  or  animal  starch. 

Glycogen  exists  constantly,  thongh  in  very  small  proportions,  in 
protoplasm  and  animal  membranes  in  general;  also,  in  white  blood- 
corpuscles  and  pus.  It  occurs  in  more  considerable  quantities  in  liver, 
muscle,  and  embryonic  tissues  after  the  third  month.  Glycogen  is  a 
white,  tasteless  powder,  soluble  in  water,  but  producing  an  opaque 
solution.  Glycogen  possesses  the  property  of  being  readily  trans- 
formed into  glucose,  to  be  ready  for  easy  oxidation.  Glycogen  with 
iodine  in  solution  Avith  iodide  of  potassium  gives  a  port-wine  color, 
which  disappears  upon  heating. 

Naturally  during  absorptive  processes  following  active  digestion, 
portal  blood  contains  more  than  the  normal  quantity — 1  per  1000. 
At  the  very  same  time  the  blood  in  the  hepatic  vein  during  the  in- 


A 

Fig.   34. — A,  Liver-cells  during  fasting.     B,  Cells  filled  with   Glycogen. 

(Heidenhain.) 

tervals  of  absorption  of  carbohydrates  contains  2  parts  per  1000. 
Within  the  hepatic-cell  protoplasm  glycogen  is  deposited.  When  an 
excess  of  carbohydrates  is  taken,  not  all  of  the  glycogen  can  be 
absorbed,  but  passes  through  into  the  general  circulation,  to  be  depos- 
ited in  the  muscles  and  other  tissues.  Muscles  may  contain  as  much 
as  1  or  2  per  cent. 

That  sugar  should  appear  in  both  portal  and  hepatic  blood  is  not 
to  be  wondered  at.  when  carbohydrates  are  fed,  but  that  it  should  still 
be  present  when  but  meats  are  given,  or  when  the  portal  vein  is  ligated 
at  the  transverse  fissure,  goes  far  to  prove  that  glycogen,  or  sugar- 
forming  animal  starch,  must  be  manufactured  Avithin  the  parenchyma 
of  the  liver.  Even  when  an  animal  is  made  to  fast,  and  at  the  same 
time  perform  very  severe  muscular  work,  so  that  glycogen  disappears 
in  muscles  and  liver,  its  presence  in  the  liver  is  soon  ascertained  again 
though  the  animal  be  fed  but  gelatin. 

Since  neither  glycogen  nor  sugar  appears  in  the  bile,  it  follows 
that  it,  or  some  transformed  product  of  it,  must  be  absorbed  into  the 


118  PHYSIOLOGY. 

blood  before  it  can  serve  any  needs  in  the  economy.  From  our  data 
we  are  led  to  believe  that  the  glycogen  is  formed  and  stored  up 
in  the  liver-cell  protoplasm,  and  the  appearance  of  sugar  is  due  to  its 
transformation  by  liver  diastase,  to  be  al)sorbed  into  the  hepatic  veins. 
Glycogen  is  formed  most  abundantly  from  carbohydrate  food  and 
from  fats  (Pfiiiger),  and  next  from  proteids.  On  a  diet  rich  in 
carbohydrates,  the  glycogen  of  the  liver  reaches  15  per  cent.,  while  in 
a  state  of  starvation  it  may  be  so  small  as  to  escape  the  tests. 

Uses. 

The  liver  is  the  chief  storehouse  of  the  carbohydrate  material. 
Thus  the  use  of  the  glycogenic  function  of  the  liver  is  supposed  to  be 
that  of  continuously  supplying  material  which  may  be  easily  oxidized 
for  the  purpose  of  maintaining  animal  heat  and  motion.  Sugar  is  a 
very  unstable  article  in  the  presence  of  oxygen  with  albuminoid  sub- 
stances. The  sugar  becomes  oxidized,  both  in  the  blood  during 
respiration  as  well  as  in  the  tissues  supplied  by  the  blood. 

DIABETES. 

Diabetes  is  a  chronic  affection  characterized  by  the  constant  pres- 
ence of  grape-sugar  in  the  urine,  an  excessive  urinary  discharge,  and 
progressive  loss  of  flesh  and  strength.  Its  exact  pathology  is  as  yet 
unknown,  but  seems  to  be  intimately  associated  with  certain  nervous 
affections,  disturbed  hepatic  and  pancreatic  functions,  sexual  excesses, 
while  heredity  also  seems  to  play  an  important  role. 

Simple  Glycosuria  must  be  dilferentiated  from  the  disease  dia- 
betes (mellitus),  since  the  former  is  but  a  temporary  condition,  and 
not  a  disease.  When  excessive  quantities  of  sugar,  maltose,  etc.,  are 
eaten  by  a  perfectly  healthy  individual,  sugar  appears  in  the  urine, 
due  to  the  fact  that  all  of  the  absorbed  sugar  cannot  be  carried  into 
the  portal  circulation  fast  enough,  so  that  some  finds  its  way  into  the 
thoracic  duct  and  l)y  it  is  emptied  at  once  into  the  general  circulation. 
Before  reaching  the  liver,  where  it  would  be  stored  up  as  glycogen,  it 
passes  through  the  kidneys,  there  to  be  promptly  eliminated.  This 
temporary  condition  has  been  termed  simple,  or  alimentanj.  glyco- 
suria. Dietary  conditions,  in  the  way  of  abstaining  from  starchy  and 
saccharine  foods,  will  promptly  eradicate  this  condition.  Simple 
glycosuria  may  also  result  from  the  inhalation  of  chloroform,  tur- 
pentine, use  of  chloral,  etc.;  it  may  be  one  of  the  conditions  following 
injury  to  the  head.  Diabetic  glycosuria  differs  in  this,  that  sugar 
is  constant  and  is  not  made  more  significant  by  the  presence  of  large 
quantities. 


DIGESTION.  119 

We  know  from  our  study  of  the  glycogenic  function  of  the  iiver 
that  glycogen  can  he  produced  from  proteids  by  synthesis  after  the 
proteid  molecule  has  been  first  broken  down. 

If  from  any  cause,  nervous  or  otherwise,  the  metabolism  of  the 
liver  is  interfered  with,  the  function  of  glycogenesis  is  disturbed,  and 
the  balance  broken,  with  the  result  of  the  appearance  of  sugar  in  the 
urine. 

Experimental  diabetes  may  be  produced  in  animals  in  various 
ways : — 

1.  By  Diabetic  Puncture. — It  was  discovered  by  Bernard  that 
certain  lesions  to  the  ccrebro-spinal  axis,  such  as  puncture  of  the  floor 
of  the  fourth  ventricle,  are  capable  of  producing  diabetic  conditions. 
After  puncture,  the  glycogen  of  the  liver  is  so  rapidly  converted  into 
sugar,  that  it  raises  the  percentage  of  sugar  in  the  ])lood  to  such  a 
degree  that  there  is  more  present  than  the  tissues  can  use  up,  and  thus 
some  of  it  finds  its  way  to  the  kidneys,  there  to  be  eliminated.  The 
increased  activity  of  the  hepatic  cells  in  transforming  the  glycogen 
is  believed  to  be  due  to  stimulation  of  the  vasomotor  center  in  the 
medulla  caused  by  the  puncture,  for  other  means  of  stimulating  this 
center  have  always  produced  temporary  diabetes.  In  man,  some  dis- 
eases of  the  brain,  particularly  those  in  the  medullary  region,  are 
characterized  by  diabetic  symptoms. 

2.  Adrenalin  Glucosuria.— Injection  of  adrenalin  produces  dia- 
betes. It  is  due  to  a  hyperglycannia.  There  is  an  increase  of  glucose, 
due  to  a  decrease  in  its  destruction.  The  ammonia  excretion  is  con- 
siderably increased.  Hence,  in  Bernard's  puncture,  there  is  an  over- 
production of  dextrose  by  the  liver;  in  pancreatic  diabetes,  a  want  of 
destruction  of  glucose  in  the  body.  In  phloridzin  diabetes,  there  is 
production  of  sugar  by  the  renal  cells,  and  in  diabetes  mellitus,  a 
hyperglycfemia,  and  this  is  due  to  a  want  of  destruction.  The  sugar 
in  diabetes  mellitus  is  derived  from  carbohydrates, .proteids,  and  fats. 

3.  Phloridzin. — This  drug  is  a  glucoside  obtained  from  the  root- 
bark  of  cherry-trees.  Powerful  results  are  obtained  after  its  admin- 
istration either  by  the  stomach  or  by  subcutaneous  or  intravenous 
injection.  With  the  appearance  of  the  sugar  in  the  urine,  there  is  a 
diminution  in  the  quantity  of  glycogen  in  the  liver.  If  the  drug 
be  administered  repeatedly,  so  that  all  of  the  glycogen  from  the  liver 
and  other  tissues  is  entirely  used  up,  and  then  an  additional  dose  be 
administered,  dextrose  will  promptly  appear. 

Phloridzin  Diabetes. — Here  the  ratio  of  dextrose  to  nitro- 
gen excreted  in  starving  animals  is  about  the  same  as  in  pancreatic 


120  PHYSIOLOGY. 

diabetes,  as  has  been  shown  by  Ijiisk.  Tlie  proportion  is  3.5  to  1. 
In  phloridzin  diabetes,  just  as  in  pancreatic  diabetes,  the  tissue  pro- 
teid  is  tlie  source  of  the  sugar,  and  these  two  forms  of  diabetes  are 
identical  as  regards  their  cause.  In  phloridzin  diabetes,  the  organism 
has  not  lost  the  power  of  oxidizing  glucose,  as  in  pancreatic  diabetes 
or  in  diabetes  mellitus.  Phloridzin  diabetes  is  not  hyperglycsemia. 
Pavy  and  Brodie  have  shown  that  the  sugar  is  formed  in  the  kidney 
itself,  out  of  serum-proteid  in  the  blood.  Phloridzin  confers  a 
secretory  power  on  the  renal  cells.  Beta-oxybutyric  acid  also  appears 
in  the  urine  after  prolonged  administration  of  phloridzin. 

To  epitomize:  Diabetes  appears  (1)  after  the  use  of  certain 
agents,  adrenalin,  iodothyrin,  and  particularly  phloridzin;  (2)  after 
inhalation  of  chloroform  and  amyl  nitrite;  (3)  after  puncture  of  the 
medulla  oblongata;  (4)  by  section  of  the  spinal  cord  above  the  exit 
of  the  hepatic  nerves,  probably  by  a  paralysis  of  the  vasoconstrictors 
of  the  liver;  (5)  by  irritation  of  the  central  ends  of  the  vagus  and 
depressor;   (G)  by  extirpation  of  the  pancreas. 

The  majority  of  cases  of  true  diabetes  terminate  fatally.  Death 
is  due  to  exhaustion  and  blood-poisoning,  producing,  just  previous 
to  the  end,  a  condition  of  complete  coma  called  acetonemia. 

Beta-oxybutyric  acid  is  the  chief  acid  in  diabetic  coma.  It  is 
believed  to  be  produced  by  the  excessive  metabolism  of  proteid. 
Whenever  a  patient  passes  more  than  five  grains  of  oxybutyric  acid 
daily  then  the  danger  of  acid  intoxication  must  be  watched.  As  to 
the  estimation  of  the  beta-oxybutyric  acid,  it  can  be  made  by  ascer- 
taining the  amount  of  ammonia  excreted,  as  it  gives  a  rough  index 
of  the  excretion  of  the  acid.  Thus,  a  daily  output  of  ammonia  of 
two  grams  corresponds  to  about  six  grams  of  the  acid. 

The  supply  of  ammonia  which  can  be  used  to  neutralize  acids 
is  derived  from  the  metabolism  of  cells  and  from  the  decomposition 
chiefly  of  meat  used  as  food.  In  the  beta-oxybutyric  acid  intoxica- 
tion, this  ammonia,  instead  of  forming  urea,  goes  to  neutralize  the 
acid,  and  is  excreted  in  the  urine  as  an  ammonium  salt. 

The  treatment  of  this  diabetic  coma  is  by  sodium  bicarbonate, 
by  intravenous  injection  and  by  mouth. 

CONJUGATED    SULPHATES. 

The  aromatic  products  which  are  formed  in  the  intestine — such  as 
indol.  skatol,  phenol,  and  eresol — are  eliminated  by  the  kidneys  in  the 
form  of  sulphates.  The  aromatic  bodies  are  absorbed  by  the  portal 
vein  and  in  the  liver  unite  with  suphuric  acid  produced  by  the  oxida- 
tion of  the  sulphur  of  the  proteids. 


DIGESTION.  121 

UREA  AND   URIC   ACID. 

The  liver  receives  products  from  the  muscles,  as  ammonium 
carbonate,  and  builds  it  into  uvea.    It  also  destroys  uric  acid. 

Jaundice  is  a  discoloration  of  the  skin  due  to  the  reabsorj)tion  of 
bile  by  the  lymphatics  of  the  liver.  This  is  usually  due  to  obstruction 
of  the  bile-ducts  by  a  catarrh,  a  calculus,  or  a  tumor.  Arsenuretted 
hydrogen  and  toluylendiamin  will  produce  jaundice. 

Influence  of  Drugs  on  Secretion  of  Bile. — Podophyllin,  aloes, 
nitrohydrochloric  acid,  ipecacuanha,  euonymin,  and  sodium  phosphate 
stimulate  the  bile-secreting  apparatus.  Other  substances,  like  calo- 
mel, stimulate  the  intestinal  glands,  but  not  the  liver-cells.  The 
best  stimulant  of  the  liver  is  bile-acids  in  ox-gall,  but  it  is  important 
to  remember  that  bile  in  the  intestine  is  liable  to  be  aljsorbed;  hence 
it  is  best  to  combine  a  purgative  with  it  to  carry  it  down  the  intes- 
tinal canal. 

THE   SUCCUS   ENTERICUS. 

By  most  physiologists  the  presence  of  a  certain  liquid  product, 
occurring  upon  the  surface  of  the  intestinal  mucous  membrane,  is 
attributed  to  the  secretory  powers  of  the  crypts  of  Lieberklihn  and 
the  glands  of  Brunner,  presumably  due  to  their  columnar  cells,  al- 
though the  real  mechanism  of  its  secretion  is  still  unknown.  To  this 
secretion  the  name  succus  entericus  has  been  commonly  given.  As 
described  by  Thiry,  it  is  "a  limpid,  opalescent,  light-yellow-colored 
fluid,  strongly  alkaline  in  reaction,  and  possessing  a  specific  gravity 
of  1.010.''  It  contains  proteid  and  mucin,  while  its  great  alkalinity 
is  due  to  the  presence  of  a  considerable  quantity  of  sodium  carbonate ; 
the  latter's  presence  is  easily  detected  by  the  effervescence,  resulting 
upon  mixture  with  dilute  acids.  The  amount  secreted  daily  is,  per- 
haps, about  two  pounds.  Erepsin,  a  ferment  found  in  the  succus 
entericus,  does  not  act  on  albumins,  but  breaks  up  albumoses,  pep- 
tones, casein,  protamin,  and  histon,  changing  them  into  leucin, 
tyrosin,  and  ammonia. 

The  succus  entericus  also  contains  a  ferment  like  that  in  yeast — 
invertin.  This  body  inverts  cane-sugar  into  dextrose  and  lawulose.  and 
maltose  into  two  molecules  of  dextrose.  This  inversion  is  necessary 
for  the  absorption  of  these  sugars.  The  succus  also  contains  another 
ferment  known  as  enterokinase — a  ferment  of  ferments. 

This  ferment  augments  the  activity  of  the  pancreatic  ferments, 
especially  the  trypsin,  by  ccmvorting  the  trypsinogen  of  the  pancreatic 


122  PHYSIOLOGY. 

juice  into  trypsin.  When  dogs  are  fed  only  on  stareli  and  fatty  foods, 
then  the  pancreatic  juice  contains  trypsinogen  with  the  object  of 
protecting  the  amylopsin  and  steapsin.  If  the  dogs  were  fed  on 
meat  exclusively,  then  the  pancreatic  juice  contained  mainly  the  fer- 
ment in  the  shape  of  trypsin.  Unlike  the  stomach,  mechanical  irri- 
tation of  the  intestine  calls  out  increased  secretion  of  the  succus 
entcricus.  But  the  intestine  has  a  special  stimulus,  and  that  is  the 
pancreatic  juice.  If  a  little  pancreatic  juice  is  inserted  into  a  loop 
of  the  intestine  for  half  an  hour,  then  a  fluid  will  be  secreted  contain- 
ing much  enterokinase.  Every  cannula  introduced  into  an  intestine 
acts  as  a  foreign  body  and  excites  a  secretion  of  water,  with  the  ob- 
ject of  washing  it  out  of  the  intestine,  and  the  amount  of  entero- 
kinase becomes  steadily  less  and  less.  Hence  a  mechanical  stimulus 
calls  out  only  water,  and  explains  the  severe  diarrhoea  of  acute  enter- 
itis, while  the  ferment  enterokinase  is  called  out  by  the  pancreatic 
juice. 

Secretin  injected  into  the  circulation  causes  a  secretion  of  intes- 
tinal juice. 

INNERVATION  OF  THE  SMALL  INTESTINE. 

If  a  piece  of  the  small  intestine  between  two  ligatures  has  the 
nerves  going  to  it  divided,  then  we  have  a  paralytic  secretion.  A 
similar  state  of  affairs  ensues  after  section  of  the  nerves  supplying 
the  submaxillary  gland.  In  the  intestinal  segment  with  its  nerves 
divided  will  be  found  an  abundant  supply  of  intestinal  juice,  contain- 
ing enterokinase  and  erepsin.  This  effect  is  probably  due  to  sec- 
tion of  nerves  which  normally  inhibit  the  secretion.  The  contigu-" 
ous  intestinal  segments  with  intact  nerves  are  nearly  empty. 

DIGESTION  IN  THE  LARGE  INTESTINE. 

Besides  the  changes  wrought  upon  the  foodstuffs  in  the  mouth, 
stomach,  and  small  intestine  by  the  various  digestive  secretions  with 
their  powerful  enzymes,  there  is  still  another  more  or  less  active 
agency  in  the  form  of  certain  bacteria  which  occur  normally  in  health 
in  varying  amounts.  Strassburger  states  that  128,000,000  bacteria 
may  be  found  in  a  day,  chiefly  in  the  large  intestine.  They  are 
swallowed  by  the  mouth  with  the  food,  drinks,  and  saliva.  The  bac- 
teria are  one-celled  organisms  and  are  produced  with  marvellous 
rapidity.  From  a  physiological  point  of  view  we  are  able  to  classify 
them   into   three   groups:     (1)    fermenting,    (2)    chromogenic,    and 


DIGESTION. 


123 


(3)  pathogenic  bacteria.     However,  only  the  ferment  bacteria  inter- 
est us. 

Bacteria  of  different  kinds  have  been  noticed  at  various  times 
throughout  the  entire  alimentary  canal  from  mouth  to  anus,  l)ut  are 


Fig.  35. — Aspect  of  an  Intestinal  Loop  befoi'e  and  after  Section  of  its 
^Serves.      (Armand  IMoreau,  from  Gley.  ) 

A,  Normal  segment  of  intestine.  B,  Same  segment  several  hours  after  sec- 
tion of  Its  nerves.  The  nerves  are  represented  by  fine  lines.  The  distension  of 
the  intestine  is  often  much  greater  than  indicated  in  the  figure. 

more  numerous  in  the  intestines,  particularly  in  the  large  one,  where 
their  action  is  very  marked  upon  matters  reaching  it,  so  as  to  give  rise 
to  the  term  '^bacterial  digestion."  In  the  stomach,  under  normal 
conditions,  the  putrefactive  activity  of  the  bacteria  is  neutralized  and 
the  germs  themselves  are  killed  by  the  free  hydrochloric  acid  of  the 


124  PHYSIOLOGY. 

gastric  juice.  It  is  in  the  intestines,  wliere  the  secretions  are  alka- 
line, that  the  best  media  are  found  for  their  culture  and  develop- 
ment. 

It  has  been  suggested  that  bacterial  digestion  was  necessary  to 
the  economy,  because  it  accomplishes  so  many  things.  But  it  has  been 
shown  by  Nuttall  that,  ])y  removing  guinea-pig  foetuses  directly  by 
incision  from  the  uterus,  and  with  antiseptic  care,  and  tlien  keeping 
them  in  a  sterile  chamber,  receiving  sterilized  air  and  fed  on  sterile 
miliv,  they  grew.  When  their  intestinal  contents  were  examined  no 
bacteria  were  found.  Hence  the  inference  is  that  bacteria  are  not 
necessary     for  good  digestion. 

The  two  chief  bacteria  are  the  lactic  acid  bacillus  and  the  colon 
bacillus.  The  former  is  found  in  the  stomach  at  times  and  the  upper 
part  of  the  small  intestine.  The  colon  bacillus  chiefly  lives  in  the 
colon.  These  bacteria  are  aerolnc;  that  is,  they  consume  oxygen  in 
the  action.  Hence  they  are  powerful  reducing  agents.  Thus  they 
take  oxygen  from  bilirubin  and  form  stercobilin.  But,  although 
these  microbes  use  oxygen,  they  can  also  live  without  it.  On  proteids 
the  bacteria  produce  by  their  action  proteoses  and  peptones,  and  from 
tyrosin  the  aromatic  bodies :  phenol  and  cresol.  Indol  and  skatol  are 
derived  from  tryptophane.  On  carbohydrates  the  bacteria  act  like 
ptyalin  and  amylopsin ;  on  fats  they  act  like  steapsin,  breaking  up 
lecithin  into  cholin.  Bacteria  in  the  stomach  and  intestine  can  set  up 
five  kinds  of  fermentation :  (1)  alcoholic;  (2)  acetic;  (3)  lactic;  (4) 
butyric;  and  (5)  a  form  of  fermentation  discovered  by  Drs.  Herter 
and  Baldwin — the  oxalic  acid  variety.  These  fermentations  may 
give  rise  to  acute  and  chronic  gastroenteritis.  In  the  intestine  the 
fermentations  will  give  rise  to  excessive  distension,  diarrhoea,  colic, 
and  a  loss  of  weight  and  strength.  The  remote  effects  of  these  fer- 
mentations will  be  an  increase  of  uric  and  oxalic  acid  in  the  urine 
and  of  the  acidity  of  the  urine  itself,  causing  frequent  urinations, 
especially  at  night.  The  best  indication  of  intestinal  putrefaction  is 
the  aromatic  or  ethereal  sulphates  which  appear  in  the  urine.  The 
easiest  test  to  detect  the  indoxyl  sulphate  of  potassium  is  the  indican 
reaction,^  These  bacteria  also  help  form  the  gases  of  the  intestine 
by  a  fermentation  of  the  food.  The  gases  in  the  intestine  are  nitro- 
gen, carbonic  acid,  hydrogen,  sulphuretted  hydrogen,  and  carburetted 
hydrogen.  The  large  intestine  is  not  necessary  to  life,  as  the  cure  of 
chronic  constipation  has  been  accomplished  by  resection  of  the  in- 
testine. 


^  Herter,  "Chemical  Pathology.' 


DIGESTION. 


125 


THE  F/ECES. 

The  foods  that  have  failed  to  be  absorbed,  after  having  remained 
about  three  hours  in  the  small  intestine,  pass  into  the  large  intestine, 
where  they  remain  for  about  twelve  hours.  The  quantity  and  con- 
sistency of  that  secreted  daily  by  an  adult  varies  within  wide  marks, 
depending  upon  the  kind  of  diet,  and  the  length  of  time  the  food- 
stuffs remain  within  the  intestine.  The  adult  eliminates  about  8 
ounces  of  moist  excrement  per  diem.  From  a  vegetable  diet  the  faeces 
are  both  softer  and  contain  a  higher  percentage  of  solids,  than  from  a 
meat  diet;  softer  because  their  irritations  to  the  intestinal  walls 
heighten  mucous  secretion  and  increase  peristalsis,  thereby  hastening 
its  passage,  to  the  detriment  of  absorption.  In  a  meat  diet  the  want 
of  this  stimulation  retards  defecation  to  such  an  extent  that  it  may 


Fig.   36. — Stool.     Collective   Microscopic   Picture.     X  350.      (Partly 
after  Nothnagel.)      (Lenhartz.  ) 

ni,  Muscle-flber.       e,  Intestinal     epithelium.       ve.  The     same,     "broken     down." 
c,  Clostridium    butyrlcum.      Ji,  Yeast,     p,   Vegetable   cells,     t.    Triple   phosphate. 


occur  but  once  in  several  days.  The  stools  are  then  small  in  amount 
and  dark  in  color.  The  stimulating  action  of  vegetables  is  what 
makes  them  so  valuable  in  mixed  diets,  though  they  are  inferior 
in  nutritive  value,  bulk  for  bulk. 

Although  the  faces  are  so  variable  quantitatively,  they  are  more 
consistent  qualitatively,  and  present  the  following  substances: — 

I.  Water. — In  health  about  75  per  cent. ;  this  becomes  much 
greater  during  diarrhoea. 


126  PHYSIOLOGY. 

II.  Indigestible  Residue  of  different  foodstuffs,  as  nuclein,  kera- 
tin, from  epidermic  structures,  }ia?matin  from  hemoglobin,  ligaments 
of  meat,  cellulose  from  vegetables,  mucin,  wood-fibers,  gums,  resins, 
and  cholcsterin. 

III.  Undigested  Food. — The  quantity  of  food  ingested  has  an 
effect.  The  more  one  eats,  the  more  likely  he  is  to  have  a  quantity 
of  undigested  matters  in  the  stool.  These  undissolved  substances  are 
usually  pieces  of  vegetables,  muscle-fibers,  connective  tissue,  and  small 
quantities  of  casein  and  fat.  These  materials  help  to  accelerate  peri- 
stalsis and  so  interfere  with  a  proper  absorption  of  those  foods  that 
would  otherwise  be  readily  taken  up. 

IV.  Mucous  Epithelial  Cells. — The  microscope  shows  these  are 
present  from  the  intestinal  surface. 

V.  Derivatives  of  Bile-salts  and  Bile-pigments. — These  are  sterco- 
bilin,  cholestcrin,  traces  of  bile-acids,  and  lecithin. 

VI.  Number  of  Putrid  Products,  as  skatol,  indol,  phenol,  volatile 
fatty  acids,  ammonia,  sulphuretted  hydrogen,  and  methane. 

VII.  Inorganic  Salts. —  These  are  salts  of  sodium,  potassium,  cal- 
cium, magnesium,  and  iron. 

VIII.  Micro-organisms. — Bacteria  of  numerous  kinds  are  present 
in  the  faeces. 

The  fasces  in  part  are  a  product  of  secretion  of  the  intestine 
itself.  Hence  the  nitrogen  of  the  faeces  comes  not  only  from  indi- 
gestible food,  but  also  from  the  secretion  of  the  intestine,  and  thus 
is  a  partial  index  of  metabolism. 

The  Color  depends  upon  the  kind  of  food  ingested;  meat  gives 
dark-brown  or  black,  vegetables  light-yellow,  faeces.  The  reaction 
is  normally  alkaline  in  adults,  while  in  infants  it  may  be  acid  and 
yet  not  pathological. 

Meconium  is  the  name  given  to  the  greenish-black  contents  of 
the  large  intestine  of  the  fcetus  which  is  expelled  at  or  after  birth. 
It  is  chiefly  concentrated  bile  with  intestinal  epithelium.  The  color- 
ing matter  is  a  mixture  of  bilirubin  and  biliverdin,  not  stercobilin. 

Defecation. — The  act  of  defecation  is,  to  a  slight  extent,  volun- 
tary, being  in  the  main  involuntary.  In  order  that  the  faeces  may 
not  stimulate  mechanically  the  sphincter  reflexes  so  that  they  relax  at 
any  time,  volition  plays  a  role.  For  there  is  a  center,  having  its  seat 
in  the  brain,  which  is  inhibitory,  and  by  voluntary  impulses  the  indi- 
vidual is  capable  of  relaxing  or  increasing  the  contraction  of  the 
externa]  sphincter  ani. 

The  inhibitory  apparatus  of  the  ano-spinal  center  arises,  accord- 


DIGESTION. 


127 


ing  to  the  latest  researches  that  I  have  made  upon  the  subject,  from 
the  locus  niger  of  the  crura  cerebri.  From  this  point  inhibitory 
fibers  descend,  some  of  which  commence  to  decussate  at  a  point  in  the 
pons  down  to  the  nib  of  the  calamus  scriptorius,  and  then  pass  down 
the  lateral  columns.  Some  of  the  fibers,  not  decussating,  also  pass 
down  the  lateral  column.  This  inhibitory  apparatus  is  under  the  con- 
trol of  a  center  in  the  cortex.  I  might  add  here  that  the  same  inhibi- 
tory apparatus  presides  over  the  sphincter  vaginge. 


Fig.  37. — Inhibitory  Apparatus  of  Ano-spinal   Center. 

A,   B,    Locus   niger   of   Cerebral   crura.     E,  F,    Inhibitory   fibers.     P,    Pons. 
M,  Medulla    oblongata.     C,  C,  Sensory    fibers.     8,  Ano-spinal    center. 

When  a  sufficient  quantity  of  fsces  has  arrived  in  the  lower  part 
of  the  rectum,  there  is  felt  a  need  of  expelling  them.  During  defeca- 
tion all  the  organs  situated  in  the  abdomen  are  compressed  so  that 
the  intestinal  contents  may  be  expelled.  Init  the  anal  sphincter,  like 
the  cardiac  sphincter  of  the  stomach,  offers  a  resistance,  and  during 
the  violent  efforts  the  vesical  sphincter  is  relaxed,  allowing  the  urine 
to  escape.  The  sensory  nerve-endings  in  the  mucous  membrane  of  the 
rectum  carry  impressions  to  the  ano-spinal  center  in  the  lumliar  cord, 
which  sends  out  motor  impulses  to  the  muscles  of  the  intestine.  At 
the  same  time  the  glottis  is  closed,  the  diaphragm  and  abdominal 
muscles  are  set  into  action,  and  the  act  of  defecation  is  accomplished. 


128 


PHYSIOLOGY. 


HUNGER  AND  THIRST. 

The  seat  of  sensations  of  hunger  is  located  in  the  epigastrium. 
The  seat  of  sensations  of  thirst  is  located  in  tlie  pharynx,  and  is 
quieted  by  intravenous  injections  of  water.  In  every  case  it  is  ad- 
mitted that  hunger  and  thirst  are  but  localized  expressions  of  a  gen- 
eral need  of  tlie  l)lood  for  food  and  drink.  The  true  seat  of  hunger 
and  thirst  is  not  known.  In  all  cases,  it  is  acknowledged  that  thirst 
is  more  painful  than  hunger,  and  it  is  more  urgent  to  satisfy  thirst 
than  hunger.  A  dog  without  food,  Init  supplied  with  water,  lives 
twice  as  long  as  a  dog  deprived  of  both  food  and  water. 


Resume  of  Action  of  the  Digestive  and  Liver  Ferments. 


Class  of  Enzyme. 

Name  of 
Enzyme. 

DiGKSTivE  Fluid 
IN  Which  Found. 

Concise  Description 
OF  Specific  Action. 

Amylases 

1.  Ptyalin. 

Saliva. 

Convert  aniyloses  (starch 
and     glycogen )      into 
dextrin,    maltose,  and 
isomaltose,      a  c  c  o  m  - 
panied  by  glucose. 

or 
Amylolytic. 

2.  Aiiiylopsin. 

Pancreatic  Jui  e. 

1.  Pepsin. 

Gastric  Juice. 

1.  Converts  proteids  into 
proteoses  and  peptones. 

Proteases 

or 
Proteolytic. 

2.  Trypsin. 

Pancreatic  Juice. 

2.  Converts  proteids  into 
proteoses,  peptones, 
and  amido-acids. 

3.  Erepsin. 

Succus  Entericus. 

3.  Converts  peptones 
into  leucin,  tyrosin,  and 
ammonia. 

Steatolytic 

or 

Lipases. 

Steapsin. 

Pancreatic  Juice 

Splits  up  neutral  fats 
into  fatty  acids  and 
glycerin. 

Coagulases. 

1.  Eennin. 

Gastric  Juice. 

1.  Coagulates  milk,  con- 
verting caseinogen  in 
presence  of  calcium 
salts  into  casein. 

2.  Rennin. 

Pancreatic  Juice. 

2.  Coagulates  milk. 

DIGESTION. 


129 


Resume  of  Action  of  the  DigeMive  and  Liver  Ferments. — {Continued.^ 


Class  of  Enzyme. 

Name  of 
Enzyme. 

Digestive  Fluid 
IN  Which  Found. 

Concise  Description 
OF  Specific  Action. 

Invertase. 

luvertin. 

Succiis  Entericus. 

Inverts  maltose  into  dex- 
trose and  Isevulose. 

Kinase,     ferment- 
iucreasiug  power 
of  other  f  e  r  - 
ments. 

Enterokinase. 

Succus  Entericus. 

Increases  the  power  of 
the  pancreatic  ferments, 
especially  the  proteo- 
lytic, by  converting 
trypsinogen  into  tryp- 
sin. 

Argiuase. 

Arginase. 

Liver. 

Converts  arginin  into 
ornothiii  and  urea. 

CHAPTER  IV. 

ABSORPTION. 

According  to  some  authors,  the  absorption  of  the  economy  in  its 
entirety  consists  of  two  processes,  the  first  of  which  has  for  its  pur- 
pose and  aim  the  introduction  into  the  blood-stream  of  fresh  material, 
for  the  nutrition  of  the  various  tissues  of  the  body.  It  is  called  ab- 
sorption from  without,  and  has  its  seat  in  the  alimentary  canal  chiefly, 
aided,  to  some  extent,  by  the  skin  and  lungs.  The  second  process 
endeavors  to  remove  from  the  numerous  tissues  of  the  body,  by  very 
gradual  measures,  the  waste-products  that  would  otherwise  accrue 
everywhere  within  the  body,  as  a  resultant  of  the  use  of  its  various 
tissues.  This  second  process  is  known  as  the  absorption  that  takes 
place  from  within,  and  has  its  seat  everywhere  within  the  tissues  of 
the  body. 

For  many  years  the  old  physiologists  entertained  the  view  that 
absorption  of  the  end-products  of  digestion  from  the  alimentary 
canal  was  purely  physical ;  that  is,  that  the  same  laws  governed  this 
bodily  function  that  do  the  passage  of  any  liquid,  with  its  contained 
dissolved  substances,  through  a  dead  membrane  placed  outside  of  the 
body.  These  processes  of  osmosis  and  filtration,  as  they  were  known 
to  the  physicist,  are  to  a  small  extent  responsible  for  some  of  the 
intestinal  absorption.  But  to-day  the  newer  view  concerning  this 
absorption  is  accepted,  whereby  it  is  believed  that  the  living  epithelial 
cells  of  the  lining  mucous  membrane  of  the  small  intestine  possess  in 
themselves,  as  living  beings,  the  power  to  exert  a  selective  action  dur- 
ing absorption ;  at  the  same  time,  they  modify  the  end-products  dur- 
ing their  passage  through  them.  They  change  the  peptones  into  al- 
bumins, and  unite  the  fatty  acids  to  glycerin.  That  the  process  was 
selective,  and  not  due  to  purely  physical  laws,  was  proved  by  the  more 
rapid  absorption  of  grape-sugar  than  sodium  sulphate,  though  the 
latter  was  many  times  more  diffusible  than  the  former. 

OSMOSIS. 

Ions. 

An  electrolyte  is  a  chemical  compound  which,  when  molten  or  in 

solution,  conducts  an  electrical  current.     When  such  a  current  passes 

through   its  solution,  the  latter  imdergoes  certain  changes  that  are 

grouped  under  the  name  of  electrolysis.     The  places  at  which  the 

(130) 


ABSORPTION.  131 

electrical  current  enters  or  leaves  the  electrolyte  are  called  electrodes : 
the  anode  and  cathode.  The  electrically  charged  particles,  the  aggre- 
gation of  which  constitutes  a  molecule  of  the  electrolyte,  are  called 
the  ions  of  the  electrolyte.  The  ions  which,  under  the  influence  of 
the  electrical  current,  migrate  to  the  anode  are  anions;  those  which 
wander  to  the  cathode,  cathions.  Thue;,  for  example,  XaCl  is  an  elec- 
trolyte; Xa  and  CI  are  its  ions;  Xa  is  the  cathion,  CI  the  anion;  in 
the  electrolysis  of  an  XaCl  solution  the  cathion,  Xa,  wanders  to  the 
cathode,  the  anion  to  the  anode.  According  to  Clausius,  the  con- 
stituents of  a  greater  or  less  numher  of  dissolved  molecules  exist  in  a 
free  state,  and  move  in  all  directions  through  the  solution  even  before 
the  passage  of  an  electrical  current.  Only  the  presence  of  the  free 
ions  makes  it  possible  that  such  a  solution  can  at  all  conduct  elec- 
tricity. If  we  dissolve  crystals  of  sodium  chloride  in  water,  a  part  of 
the  XaCl  molecules  split  into  ions :  Xa  and  CI.  If  an  electrical  cur- 
rent is  passed  through  such  a  solution  the  ions,  which  at  first  were 
moving  in  all  directions,  are  arrested  and  drawn  to  the  poles.  An 
ion  is  the  electrolytic  representative  of  an  atom. 

In  an  aqueous  solution  of  an  acid,  the  kation  is  hydrogen,  and  the 
anion  is  the  acid  radical.  In  the  solution  of  a  base,  the  kation  is 
the  metal  or  metallic  radical,  as  for  example,  ammonium  XH^.  and 
the  anion,  the  hydroxyl  OH.  In  the  solution  of  a  salt,  the  kation  is 
the  metal,  and  the  anion  the  acid  radical.  The  kations  carry  the 
positive  electricity,  and  therefore  move  towards  the  negative  pole  or 
cathode.  The  anions  carry  the  negative  electricity,  and  therefore 
move  towards  the  anode.  Suppose  we  have  an  aqueous  solution  of 
hydrochloric  acid ;  the  positive  ion  is  hydrogen  and  the  negative 
chlorine,  the  water  being  supposed  to  play  no  part  in  the  conductivity. 
If  a  solution  of  sodium  sulphate  be  electrolysed,  the  positive  ion  is 
sodium,  the  negative  SO^.  It  is  convenient  to  have  a  system  of 
names  for  the  ions  derived  from  acids,  bases,  and  salts,  which  shall 
represent  not  so  much  the  ions  as  the  particles,  but  rather  ionic  sub- 
stances. 

The  follov/ing  system  has  been  proposed,  in  which  the  names  are 
derived  directly  from  the  names  of  the  ionized  salts.  The  positive 
ions  receive  their  names  from  the  positive  radicals  of  the  salts,  acids, 
and  bases  by  the  replacement  of  the  terminations,  by  the  suffix  ion; 
for  example : — 

Hydrion,  H'  Sodion,  Xa' 

Calcion,  Ca'  Argention,  Ag' 

Ammonion,  XH/ 


132  PHYSIOLOCY. 

When  one  radical,  as  iron,  Fe,  exists  in  two  sets  of  salts,  the 
positive  ions  of  these  salts  may  be  distinguished  from  each  other  by 
a  prefix  indicating  electro-valency.  Thus,  dii'errion,  Fe" ;  trii'er- 
rion,  Fe'". 

The  names  ol'  all  negative  radicals  terminate  in  ate,  ite,  or  ide. 
Corresponding  to  these  we  have  the  tcrniinuiions  for  the  negative  ion, 
anion,  osion,  and  idion,  respectively,     ^rinis  we  oljtain: — 

Sulplianion,  SO^"  Sulphosion,  SO./' 

Siil])hidi()n,  S"  Hydrosulphidion,  HS' 

Carbonion,  CO3"  llydroxion,  Oil' 

The  function  of  ions,  by  their  ])resence  in  definite  proportion 
in  each  tissue,  is  to  preserve  tbe  "lal)ile  eijuilibriura"  of  the  colloid 
materials  of  the  proto^^lasm  on  which  its  activities  depend. 

Osmotic  Pressure. 

If  over  a  layer  of  distilled  water  we  drop  a  layer  of  colored  solu- 
tion like  copper  sulphate,  then  the  two  solutions  are  sharply  separated 
from  each  other.  But  soon  the  line  of  separation  between  the  liquids 
vanishes;  the  colorless  layer  of  water  always  becomes  smaller  and  at 
last  disappears,  so  that  the  whole  mass  is  colored.  As  soon  as  the 
color-solution  comes  into  contact  with  the  water,  then  the  molecules 
of  the  salt  l^egin  to  wander  in  the  water  and  color  it.  By  a  certain 
force  the  molecules  overcome  the  heavy  colored  particles  and  from 
heneath  are  moved  upward,  and  this  continues  until  both  fluids  have 
the  same  concentration. 

Diffusion. — When  two  miscible  crystallized  solutions  of  different 
concentration  ai'e  placed  on  either  side  of  a  perfectly  permeable  mem- 
brane, it  will  be  found  after  some  time  tliat  both  solutions  have  the 
same  concentration.  If  on  one  side  of  the  membrane  there  was  a 
20-per-ccnt.  solution  of  NaCl  and  on  the  other  side  a  10-per-cent.  solu- 
tion of  NaCl,  then  after  a  time  both  will  be  a  15-per-cent.  solu- 
tion, because  of  the  exchange  of  water  and  salt  on  each  side  of  the 
membrane.  Diffusion,  or  dialysis,  is  the  passage  of  the  molecules  of 
the  substances  in  solution. 

Osmosis. — If  now  we  separate  those  two  solutions,  a  colored  be- 
neath and  the  water  above,  by  a  partition  which  can  be  penetrated  by 
the  water  but  not  by  the  colored  particles,  then  the  partition  will  be 
pressed  upward.  If  the  partition  is  weighted  so  that  its  pressing 
upward  movement  does  not  take  place,  then  the  weight  corresponds 
to  the  pressure  exerted  by  the  particles  of  the  colored  salt.     The  pres- 


ABSORPTION. 


133 


sure  measure  that  \ya\  is  called  the  osmotic  pressure  of  the  solution, 
from  the  Greek  to  force  through.  Osmosis  is  tlie  passage  of  a  stream 
of  water-molecules  through  a  memhrane. 


Osmotic  Pressure.' 

Saw  a  Pasteur-Chamherlaud  filter  in  half.  The  cylinder  is  then 
dipped  in  dilute  hydrochloric  acid,  which  is  sucked  through  the  wall 
of  the  cylinder  by  a  hydraulic  airpump  in  order  to  remove  any  caolin 


Water 


Sugar 
solu- 
tion 


Water 


Water 


Fig.  38. — Osmometer.      (Cohen.) 

dust  that  might  choke  its  pores;  then  rinse  with  water  in  a  similar 
way.  A  beaker  is  now  filled  with  a  solution  of  potassium  ferro- 
cyanide  (139  grams  per  liter),  the  cylinder  is  dipped  into  it,  and  the 
solution  is  sucked  through  its  wall.  After  the  cylinder  has  been 
again  rinsed  in  water,  it  is  dipped  into  a  second  beaker  containing 
a  copper  solution  (349  grams  of  the  salt  per  liter),  the  inside  of  the 
cylinder  being  also  filled  with  the  solution.  A  layer  of  copper  ferro- 
cyanide  is  deposited  within  the  wall  of  the  cylinder,  and  this  pre- 
cipitate constitutes  the  semipermeable  precipitation  membrane  which 
is  permeable  for  water,  but  impermeable  for  salts. 


M^iteratiire  consulted:     Cohen's  "Physical  Chemistry,"  1903. 


134  PHYSIOLOGY. 

If  we  introduce  a  sugar  solution  into  cell  C  prepared  in  this 
manner  and  close  it  with  the  stoj)per  oi'  rubber  *S',  which  is  per- 
forated by  the  tube  AB,  then  when  (J  is  dipped  into  pure  water,  the 
sugar  endeavors  to  pass  from  the  phice  of  higher  concentration  (the 
solution)  to  that  of  lower  concentration  (the  water  without  the  cell). 
But  this  movement  is  opposed  by  the  semipermeable  membrane,  and 
in  consequence  the  sugar  exerts  a  pressure  upon  the  membrane. 
Since  this  wall,  however,  is  unyielding  and  so  .resists  the  pressure,  a 
pull  is  exerted  upon  the  water  by  the  solution  which  tends  to  dilute 
the  latter.  This  comes  to  pass  when  the  solution  enters  the  tube 
and  the  water  from  G  streams  through  the  membrane  into  the  cell 
and  dilutes  the  solution.  This  process  goes  on  until  the  resulting 
hydrostatic  pressure  in  AB  prevents  the  further  entrance  of  the 
water.  When  equilibrium  has  been  established  this  hydrostatic 
pressure  is  equal  to  the  osmotic  pressure  of  the  solution.  Con- 
versely, however,  the  latter  may  be  measured  by  ascertaining  the 
hydrostatic  pressure  which  exists  when  equilibrium  is  established; 
with  100  grams  of  water,  containing  6  grams  of  sugar,  the  osmotic 
pressure  was  3075  millimeters  of  mercury. 

Boyle-Van't  Hoff  Law. — At  constant  temperature  the  osmotic 
pressure  of  dilute  solutions  is  proportional  to  the  concentration  of 
the  dissolved  substance.  Oay-Lussac-Van't  Hoff  law  for  dilute  solu- 
tions is  as  follows:  At  constant  volume  the  osmotic  pressure  of 
dilute  solutions  increases  as  the  temperature;  or,  also,  the  osmotic 
pressure  of  dilute  solutions  is  proportional  to  the  absolute  tempera- 
ture. 

Law  of  Avogadro-Van't  Hoff. — At  the  same  osmotic  pressure 
and  the  same  ten.peTature  equal  volumes  of  dilute  solutions  con- 
tain the  same  num't'cr  of  molecules.  The  gases  have  been  shown 
long  ago  to  have  the  same  laws.  Although  osmotic  pressure  can  be 
obtained  by  the  Pasteur-Chamberland  cell  with  a  deposit  of  copper 
f errocyanide  in  its  pores,  yet  this  determination  is  inaccurate ;  hence 
we  have  recourse  to  the  determination  of  the  freezing  point. 

According  to  Arrhenius,  the  dissociated  ions  of  an  electrolyte 
in  solution  are  capable  of  exciting  pressure  as  well  as  the  undis- 
sociated  molecules. 

It  has  long  been  known  that  the  freezing-point  of  water  is  low- 
ered by  the  addition  of  soluble  substances.  The  lowering  is,  within 
certain  limits,  proportional  to  the  concentration  of  the  solution. 

For  the  biologist  the  great  importance  of  the  freezing-point 
determination  lies  in  the  fact  that  it  enables  him  to  ascertain  the 


ABSORPTION.  135 

number  of  molecules  dissolved  in  a  given  volume  of  any  body  fluid. 
A  depression  of  the  freezing-jjoint  of  Viooo  degree  corresponds  to 
an  osmotic  pressure  equal  to  0.013  atmospheres.  While  chemical 
analysis  can  tell  us  much  concerning  the  composition  of  physiolog- 
ical fluids,  it  cannot  yield  us  anything  definite  concerning  the 
osmotic  behavior  of  such  solutions.  This  becomes  intelligible  when 
we  remember  that  the  osmotic  pressure  of  a  solution  is  dependent 
upon  the  number  of  molecules  (-|-  ions)  it  contains,  and  that  this 
cannot  be  determined  by  chemical  analysis.  By  the  determination 
of  the  lowering  of  the  freezing-point  (cryoscopy)  we  have  a  direct 
means  of  accomplishing  our  end. ,  By  finding  out  the  freezing-point 
of  blood  and  of  urine  it  is  possible  to  discover  a  lessened  permeabil- 
ity of  the  kidneys  for  dissolved  molecules  and  disturbances  in  the 
secretion  of  water. 

The  freezing-point  is  determined  by  Beckman's  differential  ther- 
mometer. Thus,  the  freezing-point  of  blood-serum  of  mammals  is 
0.56°  C.  lower  than  water.  It  is  usually  expressed  by  the  Greek 
delta  A.  A  solution  of  NaCl  of  0.95-per-cent.  strength  gives  the 
same  A,  hence  the  two  solutions  have  the  same  osmotic  pressure 
and  0.95  per  cent,  of  NaCl  is  isotonic  with  mammal's  serum. 

Now,  solutions  of  any  substance  can  be  made  to  possess  the 
same  osmotic  pressure  as  any  solutfon  of  another  substance  simply 
by  changing  the  concentration,  either  increasing  it,  if  the  molecule 
of  the  substance  is  of  large  size,  or  decreasing  it  if  it  is  of  small 
size.  Solutions  which  have  the  same  osmotic  pressure  as  blood- 
serum  are  isotonic.  A  solution  which  has  a  higher  osmotic  pres- 
sure is  hypertonic,  and  that  with  a  lower  osmotic  pressure  hypotonic. 

The  osmotic  pressure  of  urine  has  the  highest  isotonic  coeffi- 
cient of  any  fluid  in  the  body,  and  its  A  is  equal  to  1.85°  C. 

The  most  important  electrolytes  present  in  blood-serum  are  the 
inorganic  salts  NaCl  and  Na^COg. 

The  freezing-point  of  defibrinated  blood  is  the  same  as  that  of 
serum ;  in  other  words,  the  presence  of  blood-corpuscles  has  no  effect 
upon  the  freezing-point.  This  ensues  because  proteids  have  an  ex- 
ceedingly low  osmotic  pressure,  although  a  high  molecular  weight. 
The  freezing-point  of  blood  does  not  change  during  ha?morrhage. 

The  osmotic  pressure  of  the  lymph  is  somewhat  greater  than 
that  of  the  blood.  An  excess  of  carbon  dioxide  in  the  blood  ele- 
vates the  osmotic  pressure. 

In  metabolism  the  large  proteid  molecules,  which  in  solution 
exert  an  exceedingly   low  osmotic  pressure,  are  split  into  smaller 


136  PHYSIOLOGY. 

ones.  In  consequence,  the  number  of  dissolved  molecules  in  the 
tissue  fluids  and  in  the  blood  is  increased,  which  causes  an  increase 
in  the  depression  of  the  freezing-point  of  these  fluids.  The  loss  of 
water  by  the  body,  through  evaporation,  has  a  similar  effect.  It  is 
the  function  of  the  kidneys  to  rid  the  body  of  this  excessive  num- 
ber of  molecules,  and  so  keep  the  osmotic  pressure  of  the  blood  and 
of  the  other  fluids  constant.  If  the  activity  of  the  kidneys  is 
decreased,  the  depression  of  the  freezing-point  of  the  blood  will 
become  greater.  A  beginning  renal  insuiiiciency  will  therefore  be 
manifested  by  an  abnormally  great  depression  of  the  freezing-point 
of  the  blood.  The  work  done  by  the  secretory  cells  of  the  kidneys 
in  secreting  the  urine,  the  osmotic  pressure  of  which  is  much  higher 
than  that  of  the  blood,  can  be  calculated  by  utilizing  the  laws  of 
osmotic  pressure.  If  the  kidneys  secrete  200  cubic  centimeters  of 
urine,  the  energy  required  amounts  to  37  kilo-grammeters;  that  is, 
the  energy  required  is  equal  to  that  expended  in  raising  a  weight 
of  37  kilograms  to  the  height  of  1  meter.  The  freezing-point  of  a  solu- 
tion of  any  substance  in  water  is  lower  than  that  of  the  water  alone. 
The  kidney-cells  separate  urine  from  the  blood  against  a  pressure 
of  a  force  about  six  times  greater  than  the  maximum  force  of  mus- 
cle. The  molecular  weight  of  a  body  can  be  determined  by  the 
depression  of  the  freezing-point. 

Another  theory  has  been  proposed  to  explain  the  low  freezing- 
point  of  urine.  Ludwig  proved  that  the  glomerulus  filters  a  nearly 
pure  solution  of  sodium  chloride,  and  that  in  the  urinary  tubules 
the  water  is  in  part  reabsorbed.  The  theory  of  Koranyi  is  that  in 
the  urinary  tubules  there  is  a  molecular  exchange  in  such  a  manner 
that,  for  each  molecule  of  urinary  constituents  coming  from  the 
blood,  there  is  a  molecule  of  sodium  chloride  passing  from  the 
tubules  into  the  blood. 

Loeb  has  shown  that  rhythmical  contractions  can  be  produced 
at  will  in  striped  muscles  of  the  frog  by  a  single  salt  in  solution. 
This  is  not  produced  by  the  salt  itself,  but  the  ions,  because  it 
occurs  only  in  solutions  of  electrolytes;  that  is,  substances  which 
dissociate.  Among  the  ions  found  in  the  blood,  he  thinks  those  of 
sodium  are  the  producers  of  rhythmical  activity.  Pure  sodium 
chloride  he  regards  as  a  poison.  If  rhythmical  activity  begun  by  it 
is  to  persist,  these  poisonous  properties  must  be  neutralized  by  cal- 
cium salts.  Loeb  thinks  calcium  and  potassium  salts  prevent 
rhythmical  activity,  but  that  they,  in  conjunction  with  sodium 
chloride,  bring  about  a  sustained  rhythm.     He  believes  the  sodium 


ABSORPTION.  137 

ion  acts  by  migrating  into  the  muscle-substance  and  combining  with 
some  part  of  it.  Hence,  when  too  many  sodium  ions  have  com- 
bined and  taken  the  place  of  a  number  of  calcium  ions  in  the  muscle, 
rhythmical  beats  cease.  The  poisonous  effects  of  Na  ions  are  antag- 
onized by  the  addition  of  a  small  amount  of  Ca  and  K  ions.  Muscles 
contract  only  as  long  as  they  contain  all  three  classes  of  ions  (iSTa, 
Ca,  and  K)  in  a  certain  proj)ortion,  which  may  vary  to  a  certain 
extent. 

Nmnerous  substances  have  been  classified  on  the  basis  of  the 
degree  which  they  possess  of  passing  through  a  membrane  while 
in  aqueous  solution.  Those  which  pass  through  freely  have  been 
found  to  be  capable  of  crystallization,  as  a  rule,  so  are  termed 
crystalloids;  those  which  are  more  tardy  in  their  osmosis  through 
a  separating  membrane  have  been  ascertained  to  be  noncrystalliz- 
able,  but  gluelike  in  nature,  hence  are  known  as  colloids.  The  col- 
loids are  very  feeble  in  all  chemical  relations,  the  reverse  being  true 
of  the  crystalloids.  Examples  of  colloids  are  seen  in  albumins, 
gelatin,  and  starch,  while  alcohol,  sugar,  and  ordinary  saline  sub- 
stances form  good  examples  of  crystalloids. 

Osmotic  Pressure  of  Proteids. — It  is  supposed  that  proteids  in 
solution  exert  little  or  no  osmotic  pressure.  The  blood  contains 
about  6  per  cent,  of  proteids.  Starling,  however,  believes  the  pro- 
teids do  exert  a  small  osmotic  pressure  equal  to  about  30  millimeters 
of  mercury.  By  reason  of  the  want  of  this  osmotic  power  the 
albumins  and  globulins  remain  in  the  blood. 

Gram-molecular  or  Mol.  Solution. — A  gram-molecule  of  any  sub- 
stance is  the  quantity  in  grams  of  that  substance  equal  to  its  mole- 
cular weight.  A  gram-molecular  solution  of  any  substance  is  the 
quantity  of  grams  of  that  substance  equal  to  its  molecular  weight. 
A  gram-molecular  solution  is  one  which  contains  a  gram  molecule 
of  the  substance  per  liter.  Thus,  58.5  grams  of  sodium  chloride 
(iSTa  =  23.05,  CI  =  35.45)  in  a  liter  is  a  gram-molecular  solution  of 
sodium  chloride. 

Physiological  Application. — The  production  of  lymph,  the  ab- 
sorption of  water,  glucoses,  and  peptone  from  the  intestine,  the 
exchanges  between  the  cells  of  the  tissues  and  the  blood  and  the 
lymph  in  the  formation  of  the  secretion,  all  require  an  explanation. 
Tn  all  these,  osmotic  pressure  plays  a  part.  "When  salt  or  glucose  is 
injected  into  the  blood-vessels,  the  first  effect  will  be  a  stream  of 
water  from  the  cells  of  the  tissues  to  the  blood,  and  the  production 
of  an  excess  of  water  in  the  blood-stream.     But  soon  the  salt  or 


138  PHYSIOLOGY. 

ghicosG  passes  out  into  the  tissnos  outside  the  blood-vessels,  and  then 
they  draw  the  water  from  the  hlood-streani.  Jn  nutrition,  the  cells 
of  the  tissues  use  up  the  materials  which  are  supplied  by  the  extra- 
cellular Iymj)h.  Jiy  tlie  concentration  the  extra-cellular  lymph  is 
lowered  and  a  stream  of  material  is  set  up  from  the  blood  to  the 
cells  outside  the  blood-vessel.  At  the  same  time,  the  cells  of  the 
tissues  are  undergoing  metabolic  changes,  the  proteid  molecule  is 
breaking  up  into  simple  molecules  of  the  character  of  crystalloids, 
such  as  urea,  phosphates,  and  sulphates,  which  pass  into  the  extra- 
cellular lymph,  increase  its  molecular  concentration,  and  by  their 
greater  osmotic  pressure  draw  water  from  the  blood  to  the  lymph; 
thus  they  increase  the  production  of  lymph.  But  as  the  broken- 
down  materials  frcmi  the  proteids  accumulate  in  the  lymph,  increas- 
ing its  molecular  concentration,  so  that  it  is  greater  than  that  of 
the  same  substances  in  the  blood,  then  they  will  diffuse  toward  the 
blood,  and  pass  out  in  the  excretions.  In  absorption  from  the  intes- 
tine, it  is  found  that  the  living  cells  of  the  intestinal  wall  modify 
absorption,  so  that  it  does  not  follow  the  law  of  diffusion  through  a 
dead  membrane. 

In  the  pathological  condition  known  as  dropsy,  there  is  pre- 
sented a  partial  example  of  filtration.  It  is  characterized  by  a 
transudation  of  the  watery  portion  of  the  blood  through  the  mem- 
branous walls  of  the  capillaries  and  small  veins  into  the  surrounding 
connective  tissues,  producing  oedema.  This  watery  element  has 
been  literally  squeezed  through  the  vessel- walls  because  of  increased 
intravascular  pressure  within  the  capillaries  and  small  veins.  The 
causes  of  this  increased  pressure  are  numerous  and  need  not  be  dealt 
with  here. 

Loeb  explains  this  oedema  by  a  greater  osmotic  pressure  in  the 
tissues  than  in  the  blood  or  lymph.  Chemical  changes  in  the  muscle 
take  place  which  increase  the  osmotic  pressure.  These  chemical 
conditions  are  the  result  of  a  diminished  supply  of  oxygen  caused 
by  deficient  circulation. 

Absorption  by  the  Stomach  and  the  Intestines. 

The  stomach  does  not  absorb  water,  but  alcohol.  Water  and 
the  salts  dissolved  in  it  are  absorbed  throughout  the  small  intestine, 
from  the  pylorus  to  the  ileo-ctecal  valve,  and  partly  by  the  large 
intestine.  So  that  the  watery  chyme  leaving  the  stomach  becomes 
gradually  thicker  as  it  travels  down  the  intestines.  The  relatively 
rapid  absorption  of  water  by  the  intestines  removes  from  the  putre- 


ABSORPTION.  139 

factive  bacteria  one  of  the  most  important  conditions  for  their  life, 
and  inhibits  their  activity.  Three  to  five  quarts  of  water  daily  can 
be  absorbed;  but  the  fa'ces  become  thin  or  paplike.  The  jejunum 
absorbs  better  than  the  ileum.  The  dilute  solutions  of  salts  are 
more  easily  absorbed  than  the  concentrated  solutions.  When  col- 
ored solutions  were  placed  in  the  intestines,  it  was  found  that  they 
passed  through  the  epithelial  cells  and  through  the  intercellular 
spaces. 

The  absorption  of  water  and  salts  from  the  intestines  does  not 
follow  the  laws  of  osmosis.  If  you  destroy  the  epithelium  with 
sodium  fluoride,  then  absorption  takes  place  only  according  to  the 
laws  of  osmosis.  When  the  epithelium  is  injured,  there  is  a 
diffusion-stream  from  the  blood,  through  the  intestinal  wall,  into  the 
intestinal  cavity;  it  seems  to  be  through  the  intestinal  epithelium. 
Intestinal  absorption  depends  upon  imbibition,  intestinal  pressure, 
and  diffusion.  The  intestinal  pressure  is  increased  by  the  respira- 
tory movements,  by  peristalsis,  and  by  the  weight  of  the  intestines. 

The  water  and  its  salts  in  solution  go  into -the  blood-vessels  of 
the  villi  because  they  are  immediately  beneath  the  basement  mem- 
brane of  the  villus,  whilst  the  chyle-vessel  is  separated  from  the 
capillaries  by  the  stroma  of  the  villus.  The  duodenum  is  the  prin- 
cipal seat  of  absorption  of  the  iron  salts,  the  spleen  their  storage- 
house,  and  the  colon   their   place  of  excretion. 

Carbohydrates. 

The  carbohydrates  are  absorbed  in  the  intestine  up  to  500 
grams  per  day.  The  monosaccharides,  dextrose,  Isvulose,  and  gal- 
actose, are  absorbed  as  such;  whilst  the  disaccharides,  cane-sugar 
and  milk-sugar,  are  first  inverted  into  dextrose,  laevulose,  and  gal- 
actose, the  latter  formed  by  the  action  of  inverting  ferments  on 
lactose.  The  chief  quantity  of  the  carbohydrates  in  the  food  is  the 
polysaccharides,  and  of  these  starch  is  a  prominent  one.  Starch  is 
not  soluble  in  either  hot  or  cold  water.  Its  cellulose  coat  must  be 
removed  by  cooking  and  baking,  and  still  it  is  not  fitted  for  absorp- 
tion; it  must  be  acted  upon  by  the  diastasic  ferments  of  the  saliva 
and  pancreatic  juice,  being  hydrolyzed  by  them,  forming  first  soluble 
starch,  then  dextrin,  isomaltose,  maltose,  and  a  little  glucose.  The 
starch  remains  but  a  short  time  in  the  mouth,  and  in  the  stomach 
the  ptyalin  acts  but  a  short  time,  because  the  free  HCl  stops  its 
activity;  hence  the  amylopsin  is  the  chief  agent  in  the  change  of 
starch  into  maltose.     Here  the  isomaltose  is  changed  into  maltose. 


140  PHYSIOLOGY. 

and  the  maltose  into  dextrose  and  lawuloso.  You  do  not  find  maltose 
in  the  blood,  notwithstanding  large  doses  of  it  by  the  mouth,  but 
glucose.  The  carbohydrates  not  absorbed  in  the  intestine,  by  the 
action  of  bacteria  undergo  acid  fermentation,  forming  acetic,  lactic, 
butyric,  carbonic  acids  and  hydrogen  gas.  Large  quantities  of 
cane-sugar  and  milk-sugar  generate  acids  which  excite  peristalsis 
and  cause  a  secretion  of  intestinal  juice,  which  produces  a  diarrhoea 
of  frequent  acid  stools  with  a  sour  odor.  The  absorption  of  sugar 
does  not  follow  the  laws  of  osmosis,  but  the  columnar  cells  of  the 
epithelium  must  exert  a  peculiar  activity,  which  temporarily  may 
be  called  vital,  until  we  can  explain  it.  If  the  blood  is  swimming 
with  sugar,  then  the  kidneys  secrete  it,  forming  alimentary  glyco- 
suria. If  more  sugar  arrives  in  the  liver  than  its  cells  can  take  up 
and  change  into  glycogen,  then  the  excess  from  the  portal  vein  goes 
into  the  hepatic  vein  and  into  the  general  circulation ;  and  as  the 
muscles  cannot  localize  and  use  it,  it  must  pass  out  through  the 
kidneys.  This  is  the  assimilation  limit  for  the  various  carbo- 
hydrates, and  it  is  different  for  the  same  individual.  The  assimila- 
tion limit  is  higher  for  glucose  and  lower  for  milk-sugar.  The  blood- 
vessels in  the  villi  are  the  places  of  absorption  of  the  carbohydrates; 
that  is,  the  portal  vein. 

Proteids. 

Albumins  can  be  absorbed  without  being  changed  into  proteoses 
and  peptones.  Injections  of  soluble  proteids  into  the  vein  are 
assimilated,  and  they  do  not  appear  in  the  urine  nor  increase  the 
urinary  nitrogen.  Yet  proteids  are  not  absorbed  as  such  in  the  pro- 
cess of  digestion,  but  are  changed  into  albumoses  and  peptones. 
Proteids  were  not  absorbed  by  the  lymph,  for  when  about  100  grams 
of  proteid  were  eaten  by  a  man,  the  lymph  escaping  by  a  fistula  was 
not  increased  in  quantity,  nor  the  amount  of  albumin  in  it  aug- 
mented. Although  proteoses  and  peptones  are  absorbed  by  the  por- 
tal  vein,  they  cannot  be  found  in  the  blood.  It  might  be  supposed 
that  the  liver  changes  them,  but  peptone  injected  into  the  portal 
vein  passes  through  the  liver  as  such,  lowers  the  blood-pressure,  and 
acts  as  a  narcotic.  Nor  are  the  albumoses  found  in  the  lymph-chan- 
nels of  the  intestine.  Albumoses  injected  into  the  circulation  reduce 
the  coagulability  of  the  blood,  lower  the  arterial  tension,  and  act 
like  a  poison.     They  are  quickly  excreted  as  such  in  the  urine. 

Since  during  absorption  of  albumoses  and  peptones  similar  toxic 
symptoms  do  not  appear,  it  must  be  inferred  that  they  are  changed 


ABSORPTION. 


141 


in  the  wall  of  the  intestine.  Here  it  is  again  the  epithelium  of  the 
intestine  that  changes  the  peptone  into  serum-albumin  and  serum- 
globulin.  The  digestion  of  proteid  is  chiefly  accomplished  by  the 
trypsin;  removal  of  the  pancreas  confirms  this.  In  a  mixed  diet  of 
milk,  meat,  eggs,  butter,  and  bread,  about  90  per  cent,  is  absorbed. 


B 


cp    str 


Fig.  39. — A,  Section  of  Villus  of  Rat  killed  during  Fat  Absorp- 
tion. (SCHAFER. )  (From  Mill's  "Animal  Physiologj',"  copyright,  1889, 
by  D.  Appleton  and  Company.) 

ep,    Epithelium,     sir.    Striated   border,      r.    Lymph-cells,     c',    Lymph-cells   in 
epitheliuni.     I,   Central  lacteal   contaiuiDg  disintegrating  corpuscles. 

B,  Mucous  IMembrane  of  Frog's  Intestine  during  Fat  absorption. 

(  SCHAFER. ) 
ep.    Epithelium,      str.    Striated    border.      C,    Lymph-corpuscles.      I,    Lacteal. 

Absorption  of  Fats. 

Whilst  the  stomach  has  a  ferment  which  can  split  up  a  small 
part  of  cmulsionized  fat  into  fatty  acid  and  glycerin,  in  steapsin 
we  have  a  ferment  which  splits  up  the  fats  into  fatty  acids  and  gly- 
cerin. The  gall  intensifies  this  action  of  steapsin.  Besides,  we  have 
sodium-soap  from  the  presence  of  that  alkali  in  the  gall,  pancreatic, 
and  intestinal  juice.  Now,  the  soap  and  fatty  acids  are  absorbed  by 
the  epithelium  of  the  villus.     It  has  been  shown  that  the  fatty  acids 


142  PHYSIOLOGY. 

in  the  epithelial  cell  are  united  with  glycerin  to  make  neutral  fats 
to  enter  the  lacteal.  Since  the  soaps  are  soluble  in  water,  they  can 
enter  the  portal  circulation  and  he  deposited  in  the  liver,  but  the 
epithelium  of  the  villus  chiefly  unites  the  fatty  acid  part  of  the  soap 
to  glycerin  to  form  neutral  fat,  whilst  the  alkali  is  excreted  into  the 
intestinal  canal,  to  again  form  more  soaps. 

The  fats  pass  between  the  capillaries  beneath  the  basement 
membrane  of  the  villus  and  enter  the  lacteal,  so  that  chyle  has  the 
finest  emulsionized  fat.  About  60  per  cent,  of  the  fat  ingested  is 
absorbed  by  the  lacteals.  Bernard  found  in  the  rabbit  that  the  bile- 
duct  opened  into  the  small  intestine  30  centimeters  above  the  open- 
ing of  the  pancreatic  duct,  and  that  the  chyle-vessels  did  not  show 
any  fat  above  the  opening  of  the  pancreatic  duct.  Dastre  bound 
the  bile-duct  in  a  dog  and  planted  the  gall-bladder  so  that  it  emptied 
into  the  middle  of  the  small  intestine.  Then  the  pancreatic  juice 
emptied  above  the  entrance  of  the  bile,  but  no  chyle  was  visible 
until  below  the  entrance  of  the  bile.  So  that  bile  plays  an  impor- 
tant part  in  the  absorption  of  fat. 

Bile  and  pancreatic  juice  united  are  the  best  agency  to  promote 
the  absorption  of  fat. 

Harley  extirpated  the  large  intestine  and  attached  the  lower 
end  of  the  ileum  to  the  rectum  in  the  dog.  The  fgeces  contained 
five  times  more  water  than  usual,  whilst  the  fats  and  carbohydrates 
were  just  as  those  in  the  normal  dog.  The  absorption  of  fats  and 
carbohydrates  was  as  usual.  The  absorption  of  albumin  was  reduced 
to  84  per  cent.,  compared  with  95  per  cent,  in  the  normal  dog.  The 
absorption  by  the  small  intestine  of  salts,  carbohydrates,  peptones, 
and  fats  was  originally  supposed  to  be  wholly  due  to  osmosis,  but 
now  it  is  held  to  be  a  function  of  the  cylindrical  epithelium ;  for  the 
destruction  of  it  by  the  fluorides  permits  osmosis  alone  to  be  active 
as  in  a  dead  membrane,  and  the  sodium  chloride  leaves  the  blood  to 
enter  the  intestine,  whilst  with  normal  epithelium  it  goes  from 
the  intestine  into  the  blood.  This  function  of  the  epithelium  we 
will,  only  temporarily,  call  vital  until  we  can  explain  it. 

The  epithelium  of  the  villus  also,  during  the  act  of  absorption, 
transforms  the  peptones  into  albumin  and  globulin  of  the  blood, 
and  unites  the  fatty  acids  to  the  glycerin  to  form  the  neutral  fats 
of  the  chyle. 

Rapidity  of  Absorption. — The  rapidity  of  absorption  has  been 
determined  by  experiment.  Thus  it  was  found  that  lithium  chloride 
may  be  diffused  throughout  all  of  the  vascular  structures  and  even 


ABSORPTION. 


143 


into  some  of  the  nouvascular  ones,  as  the  cartilage  of  the  hip-joint 
and  aqueous  himior  of  the  eye,  within  a  quarter  of  an  hour  after 
having  been  given  on  an  empty  stomach.     When  lithium  carbonate 


Fig.   40. — Laeteals  of  a   Dog  during  Digestion.      (Colin.) 

A,  Laeteals   of   mesentery.      B,  Mesenteric    glands.      C,  Efferent   chyle-ducts. 
D,   Receptaculum  chyli. 

is  taken  in  5-  or  10-grain  doses,  its  presence  may  be  detected  in  the 
urine  within  five  or  ten  minutes;  the  time  for  appearance  is  doubled, 
or  even  trebled,  when  the  substance  is  taken  on  a  full  stomach. 


144 


rilYISIULOGY, 


It  is  interesting  as  well  as  curious,  to  note  that  some  of  the 
minera    and  vegetable  poisons  are  more  readily  absorbed  from  the 

rectum  than  the  stomach.  Tims,  it 
has  been  ascertained  that  strychnine 
in  solution  will  produce  toxic  effects 
very  much  sooner  when  injected  into 
the  rectum  than  when  administered 
by  the  stomach.  When  administered 
in  solid  form  the  reverse  is  true. 

THE  LYMPHATIC  SYSTEM. 

Having  previously  dwelt  upon 
absorption  as  it  occurs  in  the  alimen- 
tary tract,  it  remains  to  turn  our  at- 
tention to  the  next  important  process 
in  the  general  absorption  of  the  body. 
It  is  the  absorption  from  within  as 
accomplished  by  the  lymphatic  sys- 
tem. By  it  as  an  instrument  those 
materials  of  the  alimentary  end-pro- 
ducts that  were  not  taken  up  by  the 
villi  are  collected  and  transported 
back  into  the  regular  blood-stream, 
while,  on  the  other  hand,  fluid  which 
has  escaped  from  the  blood-vessels 
and  has  not  been  used  by  the  tissues 
is  gathered  up  and  again  carried  back 
into  the  blood-stream.  Very  fre- 
quently this  fluid  gathered  from  the 
tissues  of  the  body  after  it  has  given 
up  much  of  its  nutriment  to  the  tis- 
sues contains  numerous  bacteria, 
pathogenic  and  otherwise,  as  well  as 
particles  of  waste-matter  from  the 
tissues.  These  are  normally  destroyed 
by  the  lymphocytes;  if  the  foreign 
particles  are  too  numerous  for  imme- 
diate destruction,  they  are  stored  up 
in  the  lymphatic  glands,  or,  more 
Fig.  4L-The  Superficial  Lym-  ^      ^^^       ^^^^til  the  Ivmphocytes 

phatics  of  the  Internal  Surface  of         i      i       -"  o     -i" 

the  Lower  Limb.     (Sappey.)  are  able  to  dispose  of  them. 


ABSORPTION. 


145 


The  watery  fluid  which  transudes  from  the  vessels,  particularly 
the  capillaries,  is  known  as  the  lymph.  It  is  this  fluid  which  bathes 
every  cell  of  all  the  tissues  to  give  them  nutriment,  while  it  carries 
away  from  these  same  tissues  the  products  of  their  activity. 


Lymphatic  Vessels. 

In  order  to  nourish  the  tissues  of  the  body,  the  plasma  of  the 
blood  is  constantly  being  osmosed  through  the  capillary  walls  into 

Longus  colli  muscle. 
Tliyroiil  //     /  //fff  i  ^  \\    \  ^  Thyro-cervical 


Costo-eervical 
artery. 


Esophagus  — i«]W 


Axillary  lym- 
phatic trunk. 


Thoracic  duct. 


Fig.   42. — Topography  of  the  Thoracic   Duct    (Zuckerhandi.) 
(  Raymond.  ) 


spaces  between  the  cells  of  the  tissues.  Each  cell  is  thus  bathed  in 
a  plentiful  supply  of  plasma,  from  which  it  absorbs  what  is  needed 
for  its  nourishment.  This  escaped  blood-plasma,  together  with  some 
white  cells  which  have  found  their  way  into  the  spaces,  constitute 
the  lymph.  To  prevent  oedema  from  its  accumulation,  as  well  as  to 
have  it  with  its  contained  impurities  reach  the  blood,  from  which  it 
may  be  excreted,  Nature  makes  use  of  a  set  of  tubes,  the  lympJiatics. 

10 


146  PHYSIOLOGY. 

These  vessels  are  found  witliin  the  hody  generally,  even  in  those 
structures  which  contain  no  blood-vessels,  as  the  cornea  of  the  eye. 
The  fluid  within  them  always  moves  in  one  direction  only:  toward 
the  lieart.  These  vessels,  whose  sources  may  he  very  different,  unite 
in  their  course  to  form  larger  vessels  until,  by  continual  union,  they 
termiiuite  in  two  large  trunks  which  empty  into  the  subclavian  veins 
at  tlieir  junction  with  the  internal  jugulars.  The  one  emptying 
into  the  left  side  is  the  thoracic  duct,  tliat  into  the  right  side  is  the 
right  luinpliaiic  trunk. 

The  large  intestine  possesses  more  l}anphatics  than  the  small, 
so  that  richness  of  lymphatics  in  a  given  organ  is  not  directly  pro- 
■  portionate  to  its  absorbent  functions.  The  number  of  lymphatics 
has  no  constant  relation  to  the  elaboration  of  products  secreted  and 
excreted  by  the  glands,  for  they  are  numerous  in  the  mamms  and 
liver,  more  scanty  in  the  kidney,  pancreas  and  thyroid,  whilst  they 
are  abundant  in  the  center  of  the  diaphragm. 

Structure  of  the  Lymphatics. 

When  the  agriculturist  Avishes  to  drain  his  wet  lowlands  he 
resorts  to  the  use  of  pipes  of  great  porosity.  These  are  buried  and 
so  arranged  that  the  moisture  of  the  soil  very  readily  finds  its  way 
into  pipes,  to  flow  along  them  and  so  be  conveyed  away.  When  the 
arrangement  of  the  pipes  is  suitable,  the  excess  of  water  is  carried 
off.  Should  the  drain-pipes  become  defective,  or  should  their  capac- 
ity l)e  less  than  that  demanded  of  them,  there  at  once  results  a  stag- 
nation with  inundation  of  the  land.  For  the  water  to  find  its  way 
from  between  the  particles  of  earth  and  sand  into  the  pipes  it  is 
necessary  that  the  latter  be  very  porous  and  permeable — a  most 
essential  factor. 

The  principle  underlying  the  structure  of  the  lymphatics  is  very 
similar  to  that  of  the  system  of  drain-pipes  of  the  agriculturist — 
namely:  porosity — for  the  aim  of  each  is  to  collect  the  excess  of 
their  respective  fluids  and  convey  the  same  to  certain  desired 
channels. 

The  lymphatics  drain  off  from  the  system  of  the  interstitial 
spaces  such  substances,  either  foreign,  or  useless,  or  harmful  to  the 
tissues,  and  deposit  them  in  the  lymphatic  glands  or  carry  them  into 
the  blood  to  be  rebuilt  or  excreted. 

This  principle  being  kept  in  mind,  the  student  can  readily  con- 
ceive the  nature  of  the  lymphatics. 

They  must  be  vessels  of  thin  walls — walls  which  allow  of  the 


ABSORPTION.  147 

easy  osmosis  of  plasma  through  them.  In  fact,  the  lymphatic  ves- 
sel-walls are  similar  in  structure  to  those  of  the  veins,  differing 
mainly  in  the  fact  that  the  former  are  thinner.  Like  the  larger 
veins,  the  larger  lymphatics  consist  of  three  coats.  The  inner  con- 
sists of  endothelium  (tunica  intima),  the  middle  coat  contains  some 
muscular  fibers  (tunica  media),  while  the  external  coat  is  connective 
tissue  (tunica  adventitia). 

Lymphatic  Capillaries. — The  walls  of  the  lymphatic  capillaries 
simply  consist  of  a  layer  of  endothelial  cells  applied  directly  to  a 
connective-tissue  framework.  In  section,  the  endothelial  cells  are 
more  prominent  and  more  turgid  than  those  of  the  blood-vessels. 
Their  nuclei  project  into  the  vascular  cavity,  which  appears  as 
though  lined  by  a  row  of  little  pearls.  Their  nuclei  are  oval.  The 
lymphatic  capillaries  are  more  easily  stained  than  the  blood-capil- 
laries by  silver  nitrate.  When  so  stained  they  appear  marked  out 
by  black  lines,  which,  like  the  sutures  of  bone,  are  sinuous.  It  is 
usual  to  compare  the  borders  of  these  cells  to  an  oak-leaf.  The 
diameter  of  the  lymphatic  capillaries  is  much  larger  than  that  of  the 
blood-capillaries. 

So  thin  and  translucent  are  the  walls  of  the  capillaries,  that  the 
clear  lymph  contained  in  them  can  be  clearly  defined. 

Like  some  veins,  the  larger  lymphatics  contain  valves  of  a 
fibrous  nature  lined  with  endothelium.  In  form,  structure,  and 
attachments  they  are  identical  with  those  of  the  veins.  Usually 
two  valves  of  equal  size  are  found  opposite  one  another;  these,  by 
their  functions,  prevent  reflux  of  the  lymph  M'hen  pressure  or  other 
disturbance  is  brought  to  bear  upon  their  course. 

Where  Xature  has  vessels  with  thin  walls  and  which  vessels  con- 
tain fluids  propelled  by  very  weak  vis  a  tcrgo,  she  must  needs  resort 
to  numerous  valves.  So  numerous  are  these  little  safeguards  that 
when  the  lymphatics  are  injected  they  present  the  appearance  of  a 
string  of  beads. 

While  dealing  with  lymphatics,  mention  must  be  made  of  those 
modified  lymphatics  known  from  ancient  times  as  the  ladeals. 
These  vessels  take  their  origin  from  the  intestines  to  empty  their 
contents  via  the  thoracic  duct  into  the  left  subclavian  vein  for 
admixture  with  the  systemic  blood.  The  lacteals  were  so  named 
from  their  white  color  at  certain  times;  that  is,  during  active  diges- 
tion, when  the  lymph-stream  is  overwhelmed  by  the  absorbed  fatty 
granules,  which  give  to  it  its  milky  hue.  The  milky-colored  fluid  has 
been  termed  chyle. 


148  PHYSIOLOGY. 

During  the  intermission  between  active  digestion  the  lacteals 
carry  pure  lymph,  and,  from  their  functions  and  structure  being 
identical  with  that  of  true  lymjjhatics,  they  deserve  to  be  classed 
with  the  latter. 

Origin  of  the  Lymphatics. 

Lymphatic  System. 

Miss  Florence  E.  Sabin  has  shown  that  the  lymphatic  system  in 
the  embryo  pig  develops  as  two  blind  diverticula  from  the  veins  of 
the  cervical  and  inguinal  regions.  These  grow  toward  the  skin  and 
widen  out  into  four  lymph-sacs,  from  which  the  final  lymphatics  pro- 
ceed. By  a  special  growth  of  the  lymphatics  along  the  dorsal  line, 
the  thoracic  duct  is  formed. 

Though  many  features  of  this  system  are  yet  obscure  and  open 
for  investigation,  it  seems  very  probable  that,  as  stated  by  Landois, 
the  lymphatics  arise  as  follows : — 

1.  Connective-tissue  Spaces. — These  are  very  numerous,  star- 
shaped  or  irregularly  branched  spaces  which  communicate  with  one 
another  by  fine  tubular  processes.  They  are  lined  with  endothelium 
and  contain  lymph  and  a  few  "wandering  cells." 

2.  Within  the  Villi. 

3.  In  Perivascular  Spaces. — The  small  blood-vessels  which  sup- 
ply bone,  central  nervous  tissue,  retina,  and  the  liver  are  themselves 
surrounded  by  lymphatic  tubes  which,  in  many  instances,  are  larger 
than  the  blood-vessels.  Between  these  tubes  and  the  blood-vessels 
there  exists  a  space  called  the  perivascular  space  of  His.  These  are 
believed  to  be  one  source  of  lymphatics,  for,  when  they  exist,  the 
passage  of  lymph-corpuscles  into  the  lymphatic  vessels  is  greatly 
facilitated. 

4.  In  the  Form  of  Interstitial  Slits  Within  Organs. — Within  the 
testicle  and  certain  other  organs  there  exist  long,  slitlike  spaces 
between  the  various  cells  and  network  of  tubules.  They  are  all, 
however,  lined  with  endothelium.  Into  these  spaces  there  is  poured 
l}Tnph  from  the  blood-capillaries  for  the  maintenance  of  the  gland- 
ular cells,  and  at  the  same  time  it  furnishes  material  for  secretion. 
From  these  little  slits  lymphatics  take  their  origin,  but  receive  inde- 
pendent walls  after  their  exit  from  the  gland-substance. 

5.  By  Means  of  Free  Stomata. — These  occur,  for  the  most  part, 
upon  the  walls  of  the  larger  serous  cavities.  Lymph  is  pumped  here 
by  the  alternate  dilatation  and  contraction  of  the  serous  surface,  due 


ABSORPTION.  149 

to  the  movements  of  respiration  and  circulation;  so  that  serous  sacs 
ma}'  be  regarded  in  a  certain  sense  as  large  lymph-cavities.  Fluids 
placed  within  these  cavities  readily  find  their  way  into  the  lymphatics. 
The  cavities  referred  to  are  those  of  the  peritoneum,  pleura,  peri- 
cardium, aqueous  chamber  of  the  eye,  and  labyrinth  of  the  ear. 

6.  In  the  mucous  membrane  of  the  nose,  larynx,  trachea,  and 
bronchi  there  have  been  noticed  open  pores  which  are  in  communica- 
tion with  the  lymphatics. 


Fig.  43. — Section  of  Dog's  Intestine,  showing  Villi.      (Caoiat. ) 

c.  Blood-vessels,    injected.      (/,  Lacteals,     injected.      Blind    end    of    villi    en- 
veloped  in   a   capillary   network   of    blood-vessels. 

Lymphatic  vessels  of  moderate  size  are  supplied  with  nutrient 
vessels  (vasa  vasorum),  which  are  distributed  to  the  external  and 
middle  coats  of  their  walls;  up  to  the  present  time  no  nerve-supply 
has  as  yet  been  ascertained  except  for  the  thoracic  duct. 

Eanvier  and  others  state  that  there  is  no  origin  of  lymphatics 
from  open  spaces  in  the  tissues.  They  believe  lymphatic  capillaries 
are  terminated  by  absolutely  closed  culs  de  sac. 


150  riivsiuLuuY. 

Lijmplndic  Glands. 

Lymphatic  glands  are  shaped  much  like  a  kidney.  The  oblique 
afferent  vessels  approach  their  convex  border,  whereas  the  efferent 
vessels,  which  are  larger  and  more  numerous,  escape  from  the  hilum 
on  their  concave  border.  Their  consistence  is  that  of  the  liver,  and 
their  color  varies  in  different  regions,  but  usually  is  a  rosy  white. 
In  size  they  vary  from  an  olive  to  those  invisible  to  the  naked  eye. 
As  age  advances,  the  glands  become  much  smaller.  Their  number 
is  600  to  700.  The  glands  are  almost  always  buried  in  a  bed  of 
adipose  connective  tissue,  usually  united  in  groups  of  three  to  six, 
or  even  ten  to  fifteen,  forming  chains  or  chaplets.  Their  situation 
is  generally  paravascular  and  paraepithelial.  A  lymphatic  gland 
consists  of  three  parts:  (1)  the  capsule,  (2)  the  cortex,  and  (3)  the 
medulla.  The  cortex  is  composed  of  a  number  of  cells,  the  majority 
of  which  are  small.  The  nucleus  is  rounded  or  quadrangular,  and 
has  a  thick  chromatin  border;  in  its  center  are  one  or  two  chromatin 
granules.  Sometimes,  but  not  always,  a  true  nucleolus  is  found. 
These  elements  are  identical  with  the  microcytes  of  blood  and  lymph 
(lymphocytes).  The  large  cells  correspond  to  macrocytes.  The 
follicles  of  the  cortex  formed  by  the  trabecula  of  connective  tissue 
have  no  proper  wall;  they  are  limited  by  the  endothelium  of  the 
lymphatic  sinus,  which  surrounds  them.  The  follicle  Avith  the  clear 
center  is  essentially  a  seat  of  cellular  reproduction,  and  it  has  been 
termed  a  germinitival  center,  a  seat  of  karyokinesis. 

The  Medulla. — The  medulla  presents  cords,  irregular  in  size, 
shape,  and  course.  These  cords  anastomose  with  each  other  and  are 
separated  from  each  other  by  large,  clear  spaces,  the  cavernous 
sinuses.  The  medullary  cords  are  central  prolongations  from  the 
cortex,  and  are  formed  of  the  same  cells,  which  are  here  sometimes 
agglomerated.  Between  the  cords  the  cavernous  sinuses  show  us 
the  best  place  for  studying  phagocytosis  of  the  gland  and  of  the 
reticulum.  The  reticulum  is  formed  by  an  anastomosis  of  cellular 
prolongations.  Some  of  the  cells  of  the  reticulum  have  an  elon- 
gated, clear  nucleus;  others  have  distinct  niiclei. 

Afferent  Vessels  of  the  Lymphatic  Gland. — The  afferent  hon- 
phatics  pass  through  the  capsule,  lose  their  tunica  adventitia  and 
muscular  coat,  and,  like  true  capillaries,  become  reduced  to  their 
endothelium.  By  the  anastomosis  of  their  capillaries  they  form  a 
vast  peripheral  sinus,  which  generally  separates  the  capsule  from 
the  follicles.     From  the  sinus,  interfollicular  branches,  which  reach 


ABSORPTION.  151 

the  medullary  part,  run  out  where  they  run  between  the  follicular 
cords,  and  finally  throw  themselves  into  the  efferent  vessels  in  the 
region  of  the  hilum.  The  efferent  lymphatic  trunks  are  less  numer- 
ous, but  larger  than  the  afferents.  Thus  the  follicles  and  follicular 
cords  appear  as  islets  which  are  plunged  into  a  vast  portal  system, 
which  bathes  them  on  every  side.  By  confluence  and  capillarization 
the  lymphatics  form  a  vast  j)ouch  around  the  glandular  substance, 
in  which  the  current  is  slowed  and  the  pressure  lessened.  In  the 
arterial  supply  it  is  seen  that  the  follicular  cords  are  pierced  in  the 
center  by  an  arteriole,  just  as  the  Malpighian  corpuscles  of  the 
spleen.  The  arteries  reach  the  cortical  layer,  surround  the  follicles, 
to  which  they  furnisli  little  branches  which  converge  toward  the  cen- 
ter like  the  spokes  of  a  wheel  towards  the  axle.  These  glands  have 
nerves  which  surround  the  follicles  and  give  off  finer  branches  reach- 
ing the  center  of  the  nodular  structure,  where  they  appear  to  term- 
inate in  free  extremities. 

Leucocytosis. — Whether  the  glandular  cells  are  fixed  leucocytes 
or  derivatives  of  the  mesodermic  elements,  they  produce  the  white 
blood-corpuscles.  The  leucocytes  are  more  numerous  in  the  efferent 
than  in  the  afferent  vessel.  There  is  a  close  relation  between  blood- 
leucocytosis,  glandular  hypertrophies,  and  the  number  of  mitoses. 
Eemoval  of  certain  important  glandular  groups  diminishes  the  num- 
ber of  leucocytes.  The  gland-cells  are  generators  of  the  lympho- 
cytes, and  the  gland  is  a  cytogenous  gland  like  the  testicle.  The 
gland  specially  produces  microcytes  (lymphocytes). 

Composition  of  the  Lymph. 

Lymph  is  a  diluted  ]jlood-plasma,  and  is  found  in  the  lymphatic 
vessels,  as  well  as  in  the  extravascular  spaces  of  the  body.  All  the 
cells  of  the  tissues  are  bathed  in  lymph.  ^Yhilst  the  generation  of 
lymph  may  be  held  to  be  from  the  blood-plasma,  yet  the  intravas- 
cular tension  may  be  increased  by  a  flow  of  water  from  the  plasma 
into  the  lymph-spaces,  or  by  a  flow  from  the  cells  of  the  tissues  into 
the  lymph-spaces  that  surround  them. 

Lymph  is  an  allmminous,  colorless  fluid,  which  contains  lymph- 
corpuscles;  these  are  identical  with  the  colorless  blood-corpuscles. 
Lymph  is  alkaline,  has  a  specific  gravity  of  about  1.015,  and  when 
drawn  from  its  vessels  it  clots,  forming  a  colorless  coagulum  of  fibrin. 
The  watery  part  of  the  lymph  is  knov.m  as  the  lymph-plasma,  which 
contains  the  three  elements  necessary  for  coagulation :  fibrinogen, 
fibrin-ferment,  and  calcium  salts.     It  is  very  similar  to  blood-plasma. 


152  PHYSIOLOGY. 

The  proteids  present  are  /ibrinutjeti,  scrum-globulin,  and  serum- 
albumin.  The  three  proteids  in  the  blood  are  diminished  in  the 
lymph,  especially  the  fibrinogen. 

The  extractives  in  lymph  are  urea,  fat,  lecithin,  cholestcrin,  and 
sugar,  with  the  inorganic  salts.  The  quaritity  of  salts  in  the  lymph 
and  the  blood  is  the  same.     The  lymphocytes  contain  glycogen. 

The  apparently  transparent  lymph  is  found  to  contain  cor- 
puscles when  examined  under  the  microscope;  to  them  the  name 
h/mpliocytes  has  been  applied.  They  have  a  large  nucleus  with  com- 
paratively little  protoplasm.  In  some  places — the  thoracic  duct,  for 
example — a  few  colored  blood-corpuscles  are  found  and  are  believed 
to  have  found  their  way  into  this  distinct  system  by  reason  of 

^-»Lymph  spaces 

\,^  -Secreting 
ceils. 

-  Blood     - 
capiliarj 

\ 
\ 

Basement 
membrane 

Fig.  44. — Diagi-am  to  Show  Relation  of  the  Secreting  Cell  of  a  Gland 
to  the  Blood  and  Lymph-supply.      (Starling.) 

diapedesis.  The  regular  lymphocytes  find  their  way  into  the  blood- 
stream, where  they  multiply  and  are  known  as  leucocytes. 

The  real  manufactories  of  these  lymphocytes  are  the  lymphatic 
glands,  whose  alveoli  contain  adenoid  tissue.  The  number  of  lym- 
phocytes is  much  greater  in  the  lymph  after  it  has  passed  through 
a  gland,  and  we  find  that  lymjDh  collected  from  regions  where  there 
are  few  glands,  as  the  lower  extremities,  is  always  poorer  in  albumin 
and  richer  in  water  than  the  lymph  in  the  large  lym2)hatic  vessels. 

For  purposes  of  analysis,  lymph  can  be  obtained  from  the  limbs, 
thoracic  duct,  and  serous  cavities.  Accidental  lymphatic  fistulge  in 
man,  as  well  as  experimental  ones  in  animals,  have  been  the  source 
of  much  lymph  for  analytical  purposes. 

The  pericardial  fluid  and  aqueous  humor  are  forms  of  lymph 
which  are  not  coagulable  except  upon  the  addition  of  fibrin-ferment. 


ABSORPTION.  153 

Cerebro-spinal  fluid  has  the  identical  appearance  of  lymph,  but 
differs  from  it  in  chemical  properties  and  composition. 

Synovial  fluid  of  joints  differs  from  true  lymph  in  that  it  con- 
tains mucin  or  mucinlike  bodies  and  a  high  percentage  of  solids. 

Chyle  is  the  term  used  to  designate  the  fluid  of  the  lacteal  sys- 
tem during  active  digestion,  particularly  of  fats.  It  is  an  opaque, 
whitish,  milky  fluid,  neutral  or  slightly  alkaline  in  reaction.  The 
color  of  the  chyle  is  due  to  the  presence  in  it  of  numerous  fatly 
granules,  each  surrounded  by  an  albuminous  envelope,  ver)-  minute, 
though  uniform  in  size.  Their  fatty  nature  becomes  evident  when 
they  are  treated  with  ether,  for  they  are  immediately  dissolved.. 
Varying  quantities  of  the  fat  give  different  shades  of  whiteness  to 
the  chyle.  Thus,  in  addition  to  the  constituents  of  the  lymph,  the 
chyle  contains  a  large  amount  of  fat,  which  is  its  characteristic  fea- 
ture. During  fasting  the  chyle  in  the  lacteals  resembles  ordinary 
lymph. 

As  the  chyle  passes  on  toward  the  thoracic  duct,  especially  when 
traversing  some  of  the  mesenteric  glands,  it  is  elaborated.  As  a 
result  there  are  fewer  fat-particles,  but  there  now  begin  to  appear 
corpuscles  to  which  the  name  chyle-corpuscles  is  applied.  Further, 
it  now  gains  the  ability  to  coagulate  sj^ontaneously.  As  the  chyle 
advances  in  the  thoracic  duct  the  corpuscles  become  more  numer- 
ous, and  the  larger  and  firmer  becomes  the  clot  when  the  chyle  is 
withdrawn  from  its  vessels.  The  clot  is  like  that  of  blood  when  only 
white  corpuscles  are  present.  Its  ability  to  coagulate  is  due  to  the 
disintegration  of  the  lymph-corpuscles  which  supply  it  with  the 
necessary  fibrin-factors. 

Flow  of  Lymph  and  Chyle. 

The  lymph  and  chyle  always  run  in  a  centripetal  direction  from 
the  periphery  to  the  center  under  the  influence  of  various  forces. 
The  villi  contract  and  push  their  contents  in  a  centripetal  course, 
aided  by  the  contractions  of  the  intestinal  muscles.  The  dilatation 
of  the  blood-vessels  at  each  contraction  of  the  heart  pushes  the 
Ij'mph  out  of  the  perivascular  spaces. 

Once  the  lymph  and  chyle  are  in  the  vessels  they  continue  to 
move  by  the  muscular  contraction  of  the  walls  of  these  vessels,  and 
this  movement  can  only  take  place  in  a  centripetal  direction  by  rea- 
son of  the  arrangement  of  the  valves.  The  lymphatic  ganglia,  by 
their  structure,  offer  a  resistance  to  the  circulation  of  the  honph, 
but  their  fibrous  covering  and  unstriped  muscles  favor  the  flow. 


154  PHYSIOLOGY. 

Cold-blooded  animals  have  lymphatic  hearts  which  act  as  motors  in 
circulating  the  lymph.  The  valves  in  the  lymphatic  vessels  are 
povt'erful  adjuvants  in  propelling  the  lymph  in  a  central  direction. 
The  respiratory  movements  have  an  influence.  At  the  time  of 
inspiration  the  flow  of  lymph,  like  the  blood,  rushes  into  the  chest, 
owing  to  the  partial  vacuum  in  the  chest.  The  pressure  by  mus- 
cular action  on  the  lymphatics  also  greatly  aids  in  the  propulsion  of 
the  lymph. 


Fig.  45. — Diminution  of  the  Flow  of  Lymph  under  tlie  Influence  of 
the  Slowing  of  the  Heart.  Dog  narcotized  with  morphia  and  chloro- 
form.    (L.  Camus.) 

E,  Irritation  of  the  peripheral  end  of  left  vagus.  El,  Drops  of  lymph  from 
thoracic  duct  by  the  vertical  lines,  P.Cg.  Pressure  in  left  carotid  equals  140 
millimeters  of  mercury. 


Lymph  moves  at  the  rate  of  about  ten  inches  per  minute,  and 
its  pressure  is  fifteen  millimeters  of  soda  solution. 

The  nervous  system  bears  a  direct  relation  to  the  lymph-stream 
in  so  far  as  it  governs  the  musculature  of  the  lymph-trunks  and  cap- 
sule and  trabecule  of  the  lymph-glands.  A  solution  of  common  ealt 
injected  beneath  the  skin  of  a  frog  will  be  rapidly  absorbed ;  but 
when  the  central  nervous  system  is  destroyed,  then  no  absorption 
takes  place. 


ABSORPTION.  155 

Drs.  Camus  and  Gley  found  in  the  sjTiipathetic,  below  the  first 
thoracic  ganglion,  nerves  which  contract  and  dilate  the  thoracic  duct ; 
usually  the  effect  is  one  of  dilatation. 

Formation  of  Lymph. 

About  1847  Ludwig  and  DuBois  Reymond  began  to  explain  the 
phenomena  of  life  by  the  law  of  physics  and  chemistry.  Since  the 
middle  of  the  eighties  of  the  last  century,  owing  to  the  failure  to 
explain  several  phenomena,  there  has  arisen  a  school  of  Neovitalists, 
who  explain  the  same  observations  as  being  due  to  vital  activity. 
The  secretion  of  l3-mph  is  one  of  these  cases  in  point. 

There  are  three  theories  which  explain  the  secretion  of  lymph: — 

1.  Ludwig's  or  the  Filtration  Theory,  which  requires  that  the 

pressure  be  higher  on  one  side  of  the  membrane  than  on  the  other. 


Fig.  46. — Dog  with  ^Medulla  Divided.      (L.  Camus  and  E.  Gley.) 

Ex,  Irritation  of  the  lower  end  of  the  thoracic  sympathetic  below  the  stel- 
late ganglion.  C.tk,  Drops  of  lymph  from  the  thoracic  duct,  Indicated  by  the 
vertical  lines.  The  experimenters  were  very  careful  that  during  the  irritation 
of  nerve  neither  the  carotid  nor  the  jugular  pressure  was  altered.  Dilatation 
of  the  thoracic  duct  by  irritation  of  the  thoracic  sympathetic,  causing  an 
acceleration   of   the   flow   of   lymph. 

The  blood-pressure  in  the  capillaries  is  greater  than  the  pressure 
outside  the  capillaries  in  the  lymph-spaces.  Hence,  the  diluted 
plasma  or  lymph  will  filter  through  the  capillaries. 

By  this  exudation  the  interstitial  pressure  always  tends  to  the 
same  height  as  the  intracapillary  pressure — the  stronger  the  intra- 
capillary  pressure,  the  stronger  the  interstitial  pressure.  On  the 
other  hand,  the  stronger  the  interstitial  pressure,  the  more  easily 
the  l}Tnpli  Avill  be  absorbed  by  the  lymphatic  capillaries.  We  must 
admit,  with  Ludwig^'s  filtration  theory,  that  the  pressure  of  the  blood 
is  a  powerful  cause  in  the  circulation  of  the  lymph,  and  this  can 
be  easily  shown  by  section  and  irritation  of  the  spinal  cord,  after  a 
cannula  has  been  introduced  into  the  thoracic  duct,  where  the  lymph- 
flow  decreases  with  the  dilatation  of  blood-vessels  on  section  of  the 
cord  and  increases  on  irritation  of  the  cut  section. 


156  PHYSIOLOGY. 

Ludwig  also  made  a  second  factor  in  his  theory,  and  that  was 
osmotic  chan<Tes  hetwecn  the  lymph  and  the  hlood. 

2.  Heidenhain's  Theory. — He  believes  filtration  of  the  plasma, 
due  to  higher  pressure  in  the  capillaries,  will  not  suffice  to  explain 
the  formation  of  lymph.  When  glucose  is  injected  into  the  blood, 
there  is  more  glucose  after  a  time  in  the  lymph  than  in  the  blood. 
He  calls  the  agents  which  cause  an  increased  secretion  of  lymph, 
lymphagogues.  He  makes  two  classes  of  these.  The  first  class  con- 
sists of  peptone,  extract  of  leeches,  and  watery  extract  of  crayfish. 
The  second  class  comprises  sugar,  sodium  chloride,  urea,  and  salts. 

The  first  class  of  lymphagogues  does  not  increase  blood-pressure 
or  affect  the  circulation,  hence  blood-pressure  could  not  be  stated 
as  the  cause  of  the  increased  flow  of  lymph.  He  ascribes  the  action 
to  a  stimulation  of  the  endothelial  cells  of  the  capillaries.  After 
action  by  the  first  class  of  lymphagogues,  the  blood-plasma  con- 
tains less  organic  principles  than  the  lymph.  The  explanation  of 
the  action  of  the  second  class  of  lymphagogues  is  as  follows:  The 
lymph-secretion  by  these  agents  is  poorer  in  proteids  than  normal 
lymph.  Whilst  the  lymphagogues  of  the  first  class  do  not  affect  the 
urinary  secretion,  those  of  the  second  class  increase  the  secretion  of 
both  lymph  and  urine  at  the  same  time.  If  injections  of  the  second 
class  of  lymphagogues  are  made  slowly  they  do  not  affect  blood-pres- 
sure. Heidenhain  explains  their  action  in  this  way:  the  crystalloid 
substances  within  the  circulation  are  gradually  secreted  into  the 
lymph-spaces  and  urinary  tubules  by  the  aid  of  the  endothelial  cells 
of  the  capillaries.  Then  the  crystalloids  in  the  lymph-spaces,  by 
their  high  osmotic  power,  attract  water  from  the  tissues. 

3.  Starling's  Theory. — In  the  limbs  the  flow  of  the  lymph  is 
very  scanty,  whilst  in  the  liver  and  the  intestinal  area  it  is  much 
more  abundant.  Starling  holds  that  the  capillaries  of  the  liver  are 
most  permeable,  the  capillaries  of  the  intestinal  wall  are  less  per- 
meable, and  the  capillaries  of  the  extremities  the  least.  Thus, 
lymph  from  the  extremities  contains  only  2  to  3  per  cent,  of  pro- 
teid,  from  the  intestines  4  to  6  per  cent,  of  proteid,  from  the  liver 
6  to  8  per  cent,  of  proteid,  which  is  nearly  as  much  as  that  of  blood- 
plasma.  Starling  explains  the  action  of  the  lymphagogues  of  the 
first  class  of  Heidenhain  (peptone,  extract  of  leeches,  and  watery 
extract  of  crayfish)  by  a  change  in  the  permeability  of  the  capillary 
wall,  as  these  agents  are  poisonous  and  alter  the  permeability  of  the 
endothelial  walls  of  the  capillaries,  especially  those  of  the  liver.  To 
account  for  the  variation  in  the  amount  of  proteids  in  the  lymph. 


ABSORPTION.  157 

Starling  puts  forth  the  permeability  of  the  capillary  wall.  The 
larger  the  pores  in  a  membrane,  the  more  permeable  the  membrane 
will  be  for  the  colloids,  and  the  richer  the  filtrate  will  be  in  organic 
material.  This  explains  the  action  of  the  first  class  of  lymphagogues 
in  producing  a  lymph  containing  more  organic  principles  than  the 
blood.  As  to  the  second  class  of  lymphagogues  of  Heidenhain,  it 
has  been  shown  that  the  intravenous  injection  of  sugar  or  sodium 
chloride  into  the  circulation  causes  a  large  amount  of  water  to  leave 
the  tissues  and  enter  the  circulation.  The  high  osmotic  pressure  of 
the  sugar  or  other  crystalloids  in  the  capillaries  causes  an  attraction 
of  water  from  the  tissue-spaces  and  from  the  tissues  themselves, 
and,  of  course,  an  hydra?mic  plethora  and  an  increased  blood-pres- 
sure, then  the  filtration  of  much  lymph,  and  necessarily  one  poor  in 
proteids.  The  amount  of  lymph  produced  is  dependent  solely  on 
two  factors:  (1)  the  intracapillary  blood-pressure  (Ludwig's  theory), 
and  (3)  the  permeability  of  the  endothelial  wall  of  the  capillaries 
of  the  circulation  (Starling's  theory). 

Absorption  by  the  Blood=vesseIs. 

Fluids  can  be  absorbed  from  the  lymph-spaces  and  from  the 
serous  cavities  into  the  blood.  This  is  due  to  the  osmotic  pressure 
exerted  by  the  proteids  in  the  blood  for  the  water  in  the  lymph- 
spaces.  In  this  way,  after  a  severe  haemorrhage,  the  blood-vessels 
are  rapidly  filled  by  the  water  absorbed  from  the  lymph-spaces.  If 
there  is  an  excess  of  fluid  in  the  blood-vessels,  part  of  it  is  excreted 
by  the  kidneys,  and  part  of  it  passes  into  the  lymph-spaces. 

Quantity  of  Lymph  and  Chyle. 

The  free  interstitial  lymph  comes  in  contact  with  three  different 
elements:  the  tissues  of  the  organ,  the  blood  of  the  capillaries,  and 
the  lymphatics.  Once  the  lymph  is  within  the  lymphatics,  none  of 
the  fluid  returns  to  the  spaces  of  the  tissues. 

The  quantity  of  lymph  is  a  varying  factor,  due  to  changes  in 
pressure  in  the  capillaries,  which,  of  course,  will  alter  the  rate  of 
filtration  of  the  blood-plasma.  In  digestion,  the  blood-plasma  is 
charged  with  the  proteids  of  digestive  activity,  and  consequently  the 
difference  of  composition  between  the  blood  and  the  lymph  will  set 
up  osmotic  pressures,  tending  to  make  each  similar  in  composition. 
Further  changes  in  the  elements  of  the  tissues,  whether  normal  or 
due  to  disease,  alter  the  composition  of  the  lymph,  and  they  also 


158  PHYSIOLOGY. 

set  up  osmotic  pressure,  tending  to  make  tlie  blood  and  lymph 
similar  in  composition. 

The  formation  of  lymph  in  the  tissues  takes  place  continually 
and  without  interruption.  The  amount  of  lymph  increases  with  the 
activity  of  the  organ  from  which  it  proceeds,  while  active  or  even 
passive  movements  of  the  muscles  greatly  increase  its  amount. 

It  may  be  roughly  stated  that  the  amount  of  lymph  and  chyle 
combined  passing  through  the  large  vessels  in  twenty-four  hourg  is 
about  2  pounds. 

Skin  and  Lungs. 

It  remains  to  consider  the  nature  of  the  absorption  that  takes 
place  through  the  skin  and  lungs.  These  avenues  are  but  subsidiary 
ones  to  the  two  greater  ones  just  mentioned:  intestinal  absorption 
and  that  along  the  lymphatic  system.  Absorption  through  them 
takes  place  from  without;  so  that  it  is  usually  classed  with  the  first 
of  the  two  processes  of  absorption  mentioned  at  the  beginning  of 
this  chapter. 

For  a  long  time  it  was  a  subject  for  much  discussion  whether 
water  was  absorbed  by  the  skin  with  the  epidermis  still  intact.  It 
was  a  rather  difficult  matter  to  ascertain,  since  the  skin  is  constantly 
giving  off  water  in  the  form  of  perspiration,  sensible  or  insensible. 
The  absorption  of  water  through  the  skin  covering  the  body  takes 
place  very  rapidly  in  the  lower  animals.  It  has  been  finally  ascer- 
tained that  absorption  of  water  docs  take  place  through  the  skin  of 
man,  but  to  a  much  less  degree  than  in  animals.  Aqueous  solutions 
of  various  drugs  when  in  simple  contact  with  the  skin  are  onl)'' 
slightly  active.  It  is  believed  that  the  great  hindrance  to  their 
absorption  is  the  presence  of  the  fat  that  is  normally  present  upon 
the  skin  and  in  its  pores  and  interstices.  If  this  be  removed  by  the 
application  of  alcohol,  ether,  or  chloroform,  physiological  effects  of 
the  drugs  are  soon  manifested. 

Inunction. — When  ointments  are  rubbed  into  the  skin  absorp- 
tion will  take  place.  Mercury,  when  applied  in  this  manner,  exerts 
its  specific  effect  upon  syphilis  and  excites  salivation ;  tartar  emetic 
so  applied  may  produce  vomiting  or  an  eruption  extending  over  the 
entire  body.  Voit  found  globules  of  mercury  between  the  layers  of 
the  epidermis  and  even  in  the  corium  of  a  person  who  had  been 
executed  and  into  whose  skin  mercurial  ointment  had  previously 
been  rubbed.     An  abraded  or  inflamed  surface  absorbs  very  rapidly. 

Under  normal  conditions  minute  traces  of  0  are  absorbed  from 


ABSORPTION.  159 

the  air;  CO,  CO2,  vapor  of  chloroform,  and  ether  may  also  be 
absorbed. 

In  dysphagia,  when  the  condition  is  so  severe  that  even  fluids 
cannot  be  taken  into  the  stomach,  immersion  of  the  patient  into  a 
bath  of  warm  water  or  water  and  milk  may  quench  the  thirst.  It 
is  well  known  that  sailors,  when  destitute  of  fresh  water,  assuage 
their  thirst  by  wetting  their  clothing  with  salt  water  and  wearing 
them  until  dry.  It  is  very  probable  that  the  effects  produced  are, 
in  a  great  measure,  attributed  to  hindrance  to  the  evaporation  of 
water  from  the  skin. 

Through  the  Lungs. — It  is  interesting  to  note  that  not  only  do 
gases  pass  through  the  epithelium  of  the  pulmonary  air-vesicles,  but 
that  fluids,  such  as  water,  may  be  absorbed  when  they  have  found 
their  way  into  the  air-passages.  The  presence  of  particles  of  car- 
bon in  the  bronchial  glands  and  other  tissues  of  the  respiratory 
apparatus  is  accounted  for  only  by  reason  of  the  open  pores:  one 
of  the  origins  of  the  lymphatic  system. 


CHAPTER  V. 

THE  BLOOD. 

Blood  is  a  red,  somewhat  viscid  fluid,  denser  than  water,  and 
apparently  composed  of  but  one  substance.  This  liquid,  which  is 
usually  spoken  of  as  the  nutritive  fluid  of  the  body,  serves  as  an 
internal  medium  of  exchange  existing  between  the  foodstuffs  found 
in  the  outer  world  and  the  cells  composing  the  various  tissues  of  the 
body.  It  was  constantly  kept  before  the  student's  attention  that 
the  main  and  ultimate  end  of  digestion  was  the  absorption  of  the 
foodstuffs  into  the  blood-stream,  not  as  proteoses  and  peptones,  but 
as  native  albumins  and  globulins — these  latter  are  the  results  of  the 
living,  vital  activity  of  the  epithelial  cells  of  the  villi  through  which 
pass  the  proteoses  and  peptones.  Thus,  into  the  blood  are  poured 
new  products  (the  work  of  digestion),  which  are  carried  by  its  circu- 
lation to  all  parts  of  the  body,  to  be  given  up  to  the  various  tissues 
having  need  of  them.  By  this  means  every  cell  receives  the  nutri- 
ment necessary  for  carrying  on  its  own  metabolic  processes,  either 
directly  or  indirectly.  For  the  student  will  remember  that  each  cell 
possesses  an  inherent  selective  capability.  From  the  pabulum  con- 
tained in  the  enveloping  lymph  it  is  able  to  take  up  those  factors 
which  it  can  work  np  into  its  own  constitution  to  form  an  integral 
part  of  itself.  These  constituents,  having  served  their  respective 
purposes,  are  no  longer  of  any  value  to  the  cell — they  are  waste-pro- 
ducts, and  as  such  must  be  gotten  rid  of.  Passing  out  from  the  cell- 
substance,  they  find  themselves  in  the  same  enveloping  lymph,  to 
be  eventually  carried  again  into  the  blood-stream  for  elimination 
through  the  excretory  activities  of  the  lungs,  kidneys,  and  skin. 
Thus,  indirectly  the  blood  is  a  medium  of  elimination  of  such  dele- 
terious products  as  urea,  uric  acid,  water,  carbon  dioxide,  etc. 

However,  the  afferent  function  of  the  blood  is  not  simply  single, 
for  it  conveys  to  the  tissues  in  addition  that  material,  all-important 
for  successful  combustion, — nam&ly,  oxygen, — which  has  been  ob- 
tained from  the  respired  air  of  the  lungs.  Among  warm-blooded 
animals  another  office  served  by  the  blood  is  to  equalize  to  a  cer- 
tain degree  the  temperature  of  the  body. 

Color. — There  are  certain  characteristics  which  distinctly  mark 
blood  from  other  fluids.  The  color  of  the  blood  of  vertebrata  is  gen- 
erally red.  Its  shade  is,  however,  not  fixed.  As  the  blood-stream 
(160) 


THE  BLOOD.  161 

passes  through  a  variety  of  tissues  and  is  subjected  to  many  differ- 
ent conditions,  its  color  varies  from  a  scarlet  red  in  the  arteries  to 
a  bluish  red  found  in  the  veins.  It  is  the  presence  of  the  oxygen 
in  combination  with  hcvmoglobin  that  gives  to  the  arterial  blood  its 
bright  color.  Lessened  oxygen  means  excess  of  carbon  dioxide,  and 
it  is  the  presence  of  the  latter  that  gives  to  venous  blood  its  char- 
acteristic bluish-red  color. 

When  normal  blood  is  drawn  from  a  blood-vessel  and  placed 
as  a  very  thin  film  upon  a  glass  slide,  it  is  found  to  be  opaque,  and 
printed  matter  cannot  be  read  through  it.  This  opacity  is  produced 
by  differences  of  refraction  possessed  by  its  several  components. 

The  healthy  red  color  of  the  nails,  conjunctiva,  lips,  ears,  and 
mucous  membranes  in  general  is  due  to  the  presence  of  the  blood. 
When  there  is  insufficient  supply  to  these  parts, — temporarily  in 
fainting  or  for  a  longer  period,  as  in  ansemia, — they  become  pale 
and  waxy  in  color.  In  asphyxia  and  certain  heart  affections  there 
is  a  want  of  proper  oxidation,  with  a  resultant  bluish  color  to  the 
above-named  parts. 

Reaction. — The  reaction  of  blood  is  alkaline.  This  alkalinity 
is  variable  in  amount.  Thus,  it  is  diminished  after  great  muscular 
exertion,  owing  to  the  formation  and  presence  in  it  of  a  large 
quantity  of  sarco-lactic  acid.  After  long-continued  ingestion  of 
soda  the  alkalinity  is  increased;  after  the  use  of  acids  it  is  dimin- 
ished. In  no  case,  however,  does  it  become  distinctly  acid.  To 
test  the  alkalinity  of  the  blood,  dry,  faintly  reddened  glazed  litmus- 
paper  is  used.  Upon  it  is  placed  a  drop  of  blood,  which  is  allowed 
to  remain  for  half  a  minute,  to  be  then  wiped  off  with  a  weak  salt 
solution.     The  result  is  a  blue  spot  upon  a  red  background. 

Blood  possesses  a  distinctly  salty  taste.  Its  alkalinity  is  chiefly 
due  to  the  presence  of  disodic  phosphate  and  bicarl)onate  of  soda. 

Specific  Gravity. — The  specific  gravity  of  normal,  healthy  blood 
varies  within  certain  limits:  for  men,  about  1.057  to  i.0G6;  for 
women,  l.Oo-t  to  1.061.  Its  density  is  influenced  by  various  factors 
and  conditions.  If  fluids  be  used  sparingly  and  a  dry  diet  eaten, 
the  density  is  increased.  It  is  also  increased  by  exercise  and  pro- 
fuse sweating.  It  falls  when  fluid  is  injected  into  the  vessels,  but 
for  a  short  time  only. 

The  temperature  of  the  blood  varies  between  07.7°  and  100°  F. 
The  cutaneous  blood-supply  is  slightly  lower  in  temperature,  while 
the  wannest  blood  is  that  in  the  hepatic  vein;  the  coldest  in  the  tip 
of  the  nose. 

u 


162  PHYSIOLOGY. 

Fresh  blood  imparts  a  decided  odor,  peculiar  to  the  animal 
from  which  it  is  drawn.  The  odor  of  blood  is  due  to  volatile  fatty 
acids  held  in  solution.  The  ett'ect  becomes  more  striking  upon  the 
addition  of  concentrated  sulphuric  acid  to  the  blood. 

Quantity  of  Blood. — From  very  early  times  the  theme  of  the 
quantity  of  blood  circulating  within  the  body  has  been  uppermost 
in  the  minds  of  physiologists  and  investigators.  By  reason  of  the 
methods  then  employed  the  results  were  inaccurate  and  difficult  of 
attainment.  Simple  bleeding  was  resorted  to,  but  deductions  de- 
pended upon  the  rapidity  with  which  the  blood  was  lost.  If  the 
animal  was  bled  very  rapidly,  then  considerable  blood  remained 
in  the  vessels.  If  the  blood  was  extracted  very  slowly,  not  only 
blood,  but  serum  from  the  lymphatic  vessels,  spaces,  and  glands  was 
obtained.     These  factors  very  materially  altered  the  calculations. 

The  accepted,  though  not  very  simple,  method,  for  determina- 
tion of  quantity  is  that  of  Welcker's.  It  is  as  follows :  The  specific 
gravity  of  the  blood  as  well  as  weight  of  the  animal  are  first  noted. 
A  cannula  is  placed  in  the  animal's  carotid  through  which  is 
extracted  a  quantity  of  blood  to  serve  as  a  sample.  This  is  defibri- 
nated,  whereupon  portions  of  it  are  diluted  at  different  known 
strengths.  The  remainder  of  the  blood  in  the  body  is  then  allowed 
to  escape,  and  is  collected  and  defibrinated.  A  normal  salt  solution 
is  next  run  through  the  vessels  and  likewise  collected.  The  entire 
body,  minus  the  stomach  and  intestines,  is  then  cut  into  very  fine 
pieces  and  extracted  with  water  for  one  or  two  days,  at  the  end  of 
which  time  the  bloody  water  is  expressed  and  added  to  the  drawn 
blood  and  washings.     The  entire  amount  is  carefully  measured. 

The  experimenter  compares  this  diluted  blood  with  the  pre- 
viously prepared  samples  of  the  diluted  blood  of  known  strength 
until  he  finds  tints  of  two  that  are  exactly  alike.  From  the  total 
quantity  of  diluted  blood  and  the  knowledge  of  what  the  sample 
contains  it  is  comparatively  easy  to  calculate  the  amount  of  blood 
contained  in  the  body.  To  this  must  be  added  the  blood  drawn  at 
first  to  make  the  various  samples.  The  weight  of  the  animal  com- 
pared with  the  above  results  gives  the  proportionate  amount. 

By  this  and  similar  computations  it  has  been  ascertained  that 
the  blood  is  equal  to  from  one-eleventh  to  one-fourteenth  of  the 
body-weight.  Approximately,  it  may  be  said  to  be  one-thirteenth 
of  the  body-weight. 

"Eoughly,  it  may  be  said  that  the  lungs,  heart,  large  arteries, 


THE  BLOOD.  163 

and  veins  contain  one-fourth ;  the  muscles  of  the  skeleton  one-fourth ; 
the  liver  one-fourth;  and  other  organs  one-fourth."     (Eanke.) 

Arterial  and  Venous  Blood  Compared. — At  this  point  the  stu- 
dent^s  attention  is  called  to  but  a  few  main  points  wherein  the  arte- 
rial and  venous  bloods  differ.  Very  conspicuoush'  stands  out  the 
marked  difference  in  color:  the  scarlet  of  arterial,  the  bluish  red  of 
venous  blood.  These  color-differences  depend  primarily  upon  the 
amount  of  oxygen-gas  contained  in  the  blood.  It  unites  with  the 
iron  of  the  blood-corpuscles  (little  bodies)  to  form  a  ver}^  unstable 
compound,  known  as  oxyhaemoglobin.  When  carbon-dioxide  gas  is 
present  it  also  forms  an  unstable  compound.  Its  color  is  dark. 
When  oxyhemoglobin  is  in  excess,  as  it  is  in  arterial  blood,  the  color 
is  a  bright  red.  When  carbon  dioxide  is  in  the  ascendancy,  the 
blood  is  bluish  red  in  color  and  the  oxygen-gas  is  present  in  dimin- 
ished amounts. 

Arterial  blood  contains  more  of  the  assimilable  products  of  the 
digestive  processes,  so  that  it  is  better  fitted  to  supply  the  cells  with 
their  proper  nutrition  and  materials  to  the  various  glands  for  their 
secretions.  It  also  contains  greater  quantities  of  salts,  fats,  and 
sugars. 

Venous  blood  contains  less  nutriment,  but  more  waste-products 
resulting  from  catabolic  processes,  particularly  urea  and  carbonic 
acid. 

Composition  of  the  Blood. — Apparently  the  blood-stream,  as 
viewed  by  the  naked  eye,  is  composed  of  one  homogeneous,  red  sub- 
stance; but  when  examined  histologically  with  the  microscope  this 
impression  becomes  entirely  dispelled.  It  is  then  found  to  be  com- 
posed in  reality  of  a  transparent  liquid  portion,  known  as  the  plasma, 
or  liquor  sanguinis,  in  which,  as  a  medium,  float  an  immense  num- 
ber of  blood-corpuscles.  The  great  majority  of  these  latter  are  col- 
ored, and  it  is  to  them  that  the  blood  owes  its  color.  There  are 
at  least  three  different  kinds  of  blood-corpuscles,  commonly  known 
as  the  red  corpuscles;  the  white  corpuscles,  or  leucocytes;  and  the 
blood-plates. 

The  red  corpuscles  of  mammalia — the  camel  and  others  of  the 
group  of  CamelidcB  alone  being  excepted — are  circular  plates,  bicon- 
cave, and  without  nuclei.  Those  of  the  camel,  birds,  and  reptiles 
are  elliptical  and  biconvex. 

Human  red  blood-corpuscles  are  biconcave,  disc-shaped  bodies 
with  rounded  edges  and  slight  central  depressions.     They  have  been 


164  PHYSIOLOGY. 

tersely  described  by  one  author  as  "circular,  biconcave,  nonnucleated 
discs." 

The  corpuscles  arc  formed  of  a  semisolid,  homogeneous,  iron- 
holding  mass  which  appears  to  have  no  membrane  or  nucleus,  for 
a  nucleus  is  normally  met  with  in  them  only  during  embryonic  life 
of  mammals  and  in  the  blood  of  the  lower  vertebrates,  as  the 
am])hibia.     In   size,   they   are    about   V.!2oo   i^ch   in   diameter   and 


Fig.    47. — Blood-corpuscles  of  Different  Animals.     (Thanuoffkr.) 

1,  Proteus.  2,  Rana  esculenta:  a,  upper  view  of  same;  b,  white  blood- 
corpuscles;  r,  side-view  of  red  corpuscles.  3,  Triton.  4,  Snake.  5,  Camel. 
6,  Turtle.  7,  Salamander.  8,  Carp.  9,  CoMtis  fossilis.  10,  Cuckoo.  11, 
Chicken.  12,  Canary  bird.  13,  Lion.  14,  Elephant.  15,  Man:  a,  upper  view 
of  same;  b,  crenated  form;  c,  white  blood-corpuscles.  16,  Horse's  cells  in 
rouleaux.     17,  Hippopotamus. 


V12000  ii^ch  in  thickness.     Various  causes  and  conditions  may,  how- 
ever, slightly  increase  or  decrease  their  size. 

Because  of  their  extremely  small  size,  the  corpuscles  are  not 
really  red  when  viewed  singly  with  the  microscope,  but  rather  of 
a  pale  yellow  or  even  greenish  tinge.  It  is  only  when  millions  of 
them  are  en  masse  that  the  characteristic  red  color  becomes  apparent : 
scarlet  red  in  arterial  blood,  purplish  red  in  venous  blood.  These 
shades  of  red  are  occasioned  by  the  varying  proportion  of  oxygen  in 


Fig.  48. 

A. — Progressive  PERNiciors  An".ei[ia.  Ehilielvs  tiiacid  stain.  Zeiss 
ofiilar  1.  oil  immersion  Via-  c,  normal  erythrocytes;  h,  megalocytes;  c,  miero- 
cytes;  d.  marked  poikilocytosis:  r.  megaloblast :  /'.  polynuclear  neutrophilic 
leucocyte.     ( Lenhartz-Brooks. ) 

B. — LiEXAL  (Splenic)  LEriCEiiiA.  o.  nonnal  erytlnucyte:  b.  nucleated 
erythrocyte,  nucleus  eccentrically  situated:  c.  polynuclear  neutrophilic  leuco- 
cytes;   (1.  eosinophilic  (myelo)  cell.     (Lenhartz-Brooks. ) 

C. — LiEXAi,  (Spi,enk)  Leuk.emia.  (il.  megalohlast  :  n.  normal  erytlu-o- 
cyte;  a2,  megaloblast,  with  anaemic  degeneration:  b.  polynuclear  leucocytes; 
t;  "marrow  cells"  (myelocytes)  ;    d,  large  lymphocyte.     (Lenhartz-Brooks.) 

I>. — AciTE  Leik.emia.  The  upper  portion  is  stained  Avith  Ehrlich's  stain 
with  eosin-hematoxylin :  the  lower  portion  is  stained  with  the  Plehii-C'henzin- 
sky's  stain.     (Lenliartz-lirooks.  i 


THE  BLOOD. 


165 


combination  with  the  haemoglobin,  with  which  the  gas  unites  very 
readily.  Because  of  this  fact  it  falls  to  the  lot  of  these  little  bodies 
to  perform  a  very  important  function  for  the  economy,  viz. :  to  con- 
vey oxygen  from  the  lungs  to  the  tissues  to  be  distributed  to  them. 
The  0  is  held  by  the  hcemoglobin  so  lightly  that  it  can  be  very 
readily  extracted  from  the  corpuscles  by  the  cells  of  the  tissues. 
Upon  the  blood  depends  the  internal  respiration  of  the  tissues  and 
all  oxidation  processes.  While  there  is  undoubted  active  oxidation 
occurring  in  the  blood  itself,  yet  the  blood  is  not  the  place  of  the 
oxidation  in  the  body.  The  cause  is  in  the  living  cells  of  the 
tissues.     In  addition  to  an  inherent  affinity  possessed  by  the  tissues 


Fig.   49. — Human  and  Ampliibian   Blood-corpuscles.      (Landois.) 

A,  Human  red  blood-corpuscles:  1,  on  the  flat;  2,  on  the  edge;  3,  rouleaux 
of  red  corpuscles.  B,  Amphibian  red  corpuscle:  1,  on  the  flat;  2,  on  edge. 
C,  Ideal  transverse  section  of  a  human  red  corpuscle,  magnified  5000  times. 
a-h,  linear  diameter;    c-d,  thickness. 


for  oxygen,  its  passage  from  the  blood  to  the  tissue-cells,  as  also 
the  passage  of  carbon  dioxide  from  the  cells  back  to  the  blood- 
stream, depend  very  materially  upon  differences  of  pressure  of  these 
two  gases  in  the  blood  and  tissues.  The  direction  is  always  from 
a  higher  pressure  to  a  lower  one. 

A  peculiar  inherent  power  and  property  of  red  corpuscles  is  to 
arrange  themselves,  when  withdrawn  from  their  retaining  vessels, 
in  the  form  of  rolls  of  coin,  adhering  to  one  another  by  some 
peculiar  affinity.  To  describe  this  condition  the  term  rouleaux  has 
been   used.     This    peculiarity   becomes   particularly   marked    when 


166  PHYSIOLOGY. 

there  is  an  inflammatory  state  of  tlie  s3'steni.     Formation  of  rouleaux 
can  ))(■  ])reveiited  by  the  iiijeclioii  of  physiological  saline  solution. 

Parasites  of  Blood-corpuscles. — In  the  red  corpuscles  of  some 
birds  and  fishes  the  microscopist  frequently  notices  small,  trans- 
parent spots.  These  are  "pseudovacuoies/"'  in  which  may  be  devel- 
oped and  later  shed  into  the  blood-stream  small  parasites.  Within 
the  red  corpuscles  of  man,  when  affected  by  malaria,  are  developed 
the  riasmodium  malariw.  Their  passage  into  the  patient's  blood- 
plasnui  marks  a  paroxysm. 

The  number  of  the  corpuscles  is  usually  spoken  of  in  terms  of 
cul)ic  millimeters;  thus,  in  man  there  are  about  5,000,000  per  cubic 
millimeter;  in  woman,  about  4,500,000.  These  figures  represent  the 
average  number  per  cubic  millimeter,  but  even  in  health  and  in  the 
same  individual  there  may  be  wide  variations  from  this  standard 
given,  to  say  nothing  of  the  extreme  diminution  experienced  in  cer- 
tain pathological  conditions. 

As  the  corpuscles  are  small  bodies  floating  in  a  liquid  medium, 
the  student  can  easily  understand  why  their  number  should  be  in 
inverse  ratio  to  the  quantity  of  plasma,  when  the  unit,  cubic  milli- 
meter, is  considered.  Copious  sweating  and  the  loss  of  much  water 
by  way  of  the  bowels  and  kidneys  occasion  a  temporary  increase  in 
their  number.  Normally,  there  is  no  difference  as  to  the  number 
of  corpuscles  in  arteries  and  veins,  provided  there  be  no  congestion 
in  the  latter. 

A  most  interesting  variation  is  that  produced  by  habitation  in 
high  altitudes.  A  two  weeks'  sojourn  in  a  high  mountain  has  been 
known  to  show  an  increase  from  5,000,000  to  7,000,000  per  cubic 
millimeter.  This  is  accounted  for  Ijy  a  real  increase  in  the  manufac- 
ture of  corpuscles.  In  chlorosis  and  pernicious  anaemia  the  corpus- 
cular count  falls  considerably.  A  decrease  to  half  a  million  per  cubic 
millimeter  is  the  lowest  limit  compatible  with  life. 

Life-cycle  of  the  Red  Corpuscles. — The  life  of  the  red  corpuscle 
is  unknown.  In  experimental  transfusion  the  red  corpuscles  disap- 
pear at  the  end  of  a  variable  period.  The  destruction  of  blood- 
corpuscles  in  extravasations  does  not  give  us  any  precise  results. 
Observing  the  differences  in  color,  consistency,  and  chemical  reac- 
tion, it  is  found  that  they  correspond  to  the  different  degrees  of 
development.  This  shows  that  in  the  blood  there  is  a  constant 
destruction  and  renewal  of  the  corpuscles. 

As  to  the  place  of  destruction  of  the  red   corpuscles,  certain 


THE  BLOOD. 


167 


facts  show  that  the  liver  and  spleen  seem  to  he  places  for  the  accom- 
plishment of  it. 

Counting-  Red  Corpuscles. — Various  methods  have  been  devised 
for  connting-  the  number  of  corpuscles,  the  instruments  used  receiv- 
ing the  name  lia'macijtometers.  Modifications  are  numerous,  but 
underlying  all  of  them  is  one  main  principle,  namely:  the  actual 
counting   of    the    corpuscles  within   a   certain   measured   bulk.     To 


Fig.   50. — Ilasmacytometer  of  Thoma-Zeiss.      (L.\housse.) 

-l,  Capillary  glass  tube.  B,  A  glass  slide  upon  which  is  a  covered  disc 
accurately  ruled  so  as  to  present  1  square  millimeter  divided  into  100  squares 
of  ^/oQ  millimeter  each.  1,  Blood  is  drawn  up  to  this  point.  101  represents 
normal  saline-solution  drawn  up  the  tube,  mixed  with  the  blood  drawn  up  to 
1.     In  101  parts  the  blood  forms  1  part. 

preserve  the  shape  and  integrity  of  these  little  bodies  during  the 
technique  it  is  necessary  to  dilute  the  sample  of  blood  with  some 
solution  whose  specific  gravity  exactly  equals  that  of  the  blood- 
serum.  Some  of  this  blood-solution  is  then  placed  upon  a  grad- 
uated slide  beneath  a  microscope  for  counting,  when  the  number 
per  cubic  millimeter  is  easily  computed. 


1G8  PHYSIOLOGY. 

At  this  point  the  attention  of  tlie  student  will  be  directed'  to 
but  two  instruments:  (1)  the  Thoma-Zeiss  apjiaratus,  aiid  {2)  the 
Daland  hu'iiiatocrit. 

1.  Tuoaia-Zkiss  Apparatus. — The  apparatus  consists  of  two 
separate  and  distinct  parts:  a  capillary  tube  and  a  counting  cham- 
ber. The  tube  is  for  the  purpose  of  measuring  the  amount  of  blood 
whose  corpuscles  are  to  be  counted.  By  it  also  is  accomplished  the 
proper  dilution  in  the  upper,  bulbed  chamber.  The  capillary  por- 
tion of  the  tube  is  graduated  to  0.5  and  1.0  marks.  Just  above  the 
capillary  portion  of  the  instrument  is  the  bulbous  portion,  contain- 
ing a  small  glass  ball  to  assist  in  the  thorough  mixing  of  blood  and 
diluting  normal  saline  fluid.  Just  above  the  bulb  is  the  101  mark. 
For  drawing  both  blood  and  the  diluting  saline  into  the  apparatus 
there  is  attached  a  piece  of  rubber  tubing  with  a  suitable  mouth- 
piece. With  the  blood  up  to  the  1.0  mark  and  enough  diluting 
saline  to  bring  the  whole  quantity  of  liquid  to  101,  the  dilution  is 
1  to  100. 


Fig.  51. — Daland's  lisematocrit. 

The  second  portion  of  the  instrument,  known  as  the  counting 
chanihcr,  is  constructed  so  as  to  enable  one  to  count  under  the  micro- 
scope all  the  cells  in  a  known  bulk  of  the  diluted  blood.  In  the 
center  of  a  thick  glass  slide  is  cemented  a  cover-glass  of  accurately 
measured  thickness  with  a  hole  in  the  center  of  about  1  centimeter 
in  diameter.  In  the  central  area  of  this  cover-glass  there  is  also 
cemented  to  the  glass  slide  a  glass  disc  about  2  millimeters  smaller 
in  diameter  and  exactly  V^q  millimeter  thinner  than  the  cover-glass. 
The  glass  shelf  being  exactly  ^/^o  millimeter  thinner  than  the  cover- 
glass,  it  will  readily  be  seen  that  if  a  second  loose  cover-glass  be 
laid  upon  the  first,  the  under  surface  of  this  loose  cover-glass  will 
be  exactly  ^/^q  millimeter  above  the  upper  surface  of  the  glass  disc. 
In  this  way  there  is  secured  a  layer  of  fluid  ^/k,  millimeter  in  depth. 
Furthermore,  1  square  millimeter  of  the  surface  of  the  disc  is  out- 
lined and  subdivided  by  intersecting  lines  into  400  small  squares. 
For  convenience  in  counting,  every  fifth  row  of  squares  is  divided 
into  two  by  an  additional  line.  The  volume  of  diluted  blood  above 
each  square  of  the  micrometer  will  be  ^Aooo  cubic  millimeter.  The 
average  of  10  or  more  squares  is  then  ascertained,  which  result  is 


THE  BLOOD. 


169 


multiplied  by  4000  times  100  to  give  the  number  of  corpuscles  in  a 
cubic  millimeter  of  undiluted  blood. 

The  H.iiMATOCRiT. — A  rapid  approximate  determination  of  the 
relative  percentage  of  the  corpuscles  may  be  made  by  Daland's 
iiistrument.  The  blood  is  sucked  up  the  graduated  tube  without 
dilution  and  then  centrifuged.  The  corpuscles  rapidly  accumulate 
at  the  end  of  the  tube  in  an  almost  solid  mass,  and  their  collective 
volume  can  be  directly  read  off.  The  estimate  can  be  made  with  a 
small  quantity  of  l)lood,  and  is,  therefore,  capable  of  being  used  for 
clinical  jnirposes.  Daland  found  that  50  was  normal;  this,  multi- 
plied by  100,000,  gives  the  number  of  corpuscles  in  1  cubic  milli- 
meter. 


Fig.  52. — Red  Blood-corpuscles.      (Landois.) 

a,  1),  Normal    human    red    corpuscles   with    the    central    depression  more    or 

less    in    focus,      c,  (I,  e,    Mulberry    forms.       y,  li,  Crenated    corpuscles.  k.  Pale 

decolored  corpuscles,      i,  Stroma.      /,  Frog's  corpuscles  acted  upon  by  a  strong 
saline  solution. 


Experiments  Upon  the  Blood. — Points  of  interest  to  the  physiol- 
ogist particularly  and  to  the  clinician  incidentally  have  been  dis- 
closed as  the  results  of  some  simple  experimental  work  upon  the 
blood-corpuscles.  Each  red  corpuscle  is  seen  to  be  composed  of  a 
fine  meshwork,  or  stroma,  consisting  of  noncolored,  homogeneous 
protoplasm.  Scattered  throughout  this  framework  is  the  iron- 
holding  pigment,  which  gives  color  to  the  corpuscle  and  is  the  sub- 
stance with  which  the  oxygen-gas  enters  into  loose  combination. 
Any  reagent  which  is  able  to  sever  the  union  between  stroma  and 
haemoglobin  causes  the  latter  to  pass  into  solution  in  the  plasma. 
The  once-red  corpuscles  then  appear  as  transparent  bodies.  This 
makes  the  blood  dark  red,  but  transparent,  since  the  coloring  mat- 
ter is  in  solution.  When  the  blood  is  in  this  condition  it  is  said 
to  be  'lake-colored."  Laky  blood  may  also  be  produced  upon  the 
injection  of  the  blood-serum  of  one  animal  into  the  blood  of  another 


170  PHYSIOLOGY. 

kind,  the  serum  having  the  i)ower  to  destroy  the  red  corpuscles. 
'JMie  term  "globulicithii  action"  covers  tliis  property  of  the  serum. 

The  first  elTect  of  pure  ivaler  upon  red  corpuscles  is  to  produce 
a  very  obvious  change  in  shape.  From  a  discoid  form,  they  hecome 
spherical,  or  nearly  so.  After  sojne  time  the  luenioglobin  becomes 
dissolved  out,  leaving  the  corpuscles  transparent:  shadow-corpuscles. 
The  knowledge  thus  gained  led  to  further  research  to  find  some 
solution  which  will  not  all'eet  the  corpuscles. 

Isotonic  Solutions. — To  prevent  "laking"  of  the  blood  normally 
there  must  be  a  certain  degree  of  concentration  of  the  medium 
immediately  surrounding  the  corpuscles  so  that  just  sufficient  water 
is  maintained  within  tlie  corpuscles  as  is  needed.  If  by  the  addi- 
tion of  distilled  water  or  other  reagents  this  degree  of  concentration 
is  changed  so  that  the  balance  is  broken,  then  too  much  water  enters 
the  corpuscle.  There  immediately  follows  a  change  in  shape,  with 
forcing  out  of  the  pigment.  A  solution,  containing  just  enough  of 
salts  so  that  the  corpuscles  are  neither  altered  in  shape  nor  lose 
their  haemoglobin,  is  said  to  be  "isotonic."  The  percentage  of  jSTaCl 
necessary  to  generate  such  a  solution  is,  for  frogs'  blood,  0.65  per 
cent.;  for  blood  of  man,  0.95  per  cent. 

The  action  of  certain  organic  substances  is  of  considerable 
importance.  Thus,  bile  and  the  alkaline  salts  of  the  biliary  acids 
have  the  power  to  dissolve  and  destroy  the  red  corpuscles  with 
phenomena  which  resemble  those  produced  by  the  action  of  chloro- 
form. Urea  in  solution,  digitalin,  saponin,  and  venom  of  snakes 
also  destroy  them. 

As  to  vitality,  it  is  known  that  the  corpuscles  of  the  blood  that 
have  escaped  from  the  circulatory  system,  as  well  as  those  from 
defibrinated  blood,  when  reintroduced  into  the  living  blood-stream, 
retain  their  vitality. 

THE  WHITE  CORPUSCLES, 

The  white  corpuscles  are  colorless,  spherical  little  bodies  which 
are  a  little  larger  than  the  red  ones  and  much  less  numerous.  Each 
is  about  V0500  inch  in  diameter  and  is  composed  of  granular  proto- 
plasm that  is  highly  retractile  and  without  any  enveloping  mem- 
brane. 

In  striking  contrast  to  the  erythrocytes,  the  leucocytes  possess 
not  only  one,  but  usually  three  nuclei;  even  four  are  not  uncom- 
mon.    Within  the  nuclei  may  be  defined  several  distinct  nucleoli. 


THE  BLOOD.  171 

When  examining  a  section  of  blood,  it  is  at  once  a  striking  fea- 
ture how  few  are  the  white  as  compared  with  the  red  corpuscles. 
In  the  average  field  but  three  or  four  are  found,  while  at  the  same 
time  hundreds  of  erythrocytes  are  noticed.  The  average  is  biit  1 
white  for  every  500  or  600  red  ones. 

This  proportion  does  not  pretend  to  convey  an  accurate  idea  of 
their  relationship  because  of  the  frequent  fluctuations  of  the  white 
corpuscles  even  in  a  single  day.  They  increase  during  digestion  and 
diminish  during  abstinence. 

Bleeding,  lactation,  quinine,  local  suppuration,  pregnancy,  and 
leucocythsemia  increase  the  white  corpuscles;  their  number  is  dimin- 
ished by  large  doses  of  mercury. 

The  proportionate  number  of  leucocytes  that  is  found  in  blood 
drawn  from  its  containing  vessels  is  no  criterion  of  the  number 
found  within  the  blood-stream.  As  soon  as  blood  is  drawn  from  the 
body,  for  no  accountable  reason  as  yet  known,  an  immense  number 
of  white  corpuscles  disappears.  It  is  stated  that  there  remains  but 
one-tenth  of  the  number  previously  found  in  circulation. 

Colorless  corpuscles  are  not  essentially  peculiar  to  the  blood- 
stream nor  to  be  found  only  in  it,  for  similar  corpuscles  are  found 
in  lymph,  chyle,  adenoid  tissue,  the  marrow  of  the  long  bones,  and 
also  as  wandering  cells  in  connective  tissue,  drawn  thither  by  inflam- 
mation and  by  bacteria. 

Varieties. — According  to  Ehrlich,  they  may  be  separated  into 
tliree  groups,  the  basis  of  classification  depending  upon  the  staining 
prodivities  of  the  granules  held  within  the  cytoplasm.  To  the  first 
group  he  gave  the  name  eosinophiles,  because  the  granules  of  this 
class  of  corpuscles  stain  best  with  acid  aniline  dyes.  The  hasophiles 
comprise  the  second  group  and  include  those  staining  best  with  hasic 
dyes.  Last  come  the  neutrophiUs;  their  granules  are  capable  of 
being  colored  only  by  the  presence  of  neutral  dyes.  This  classifica- 
tion is  a  very  popular  one,  and  holds  a  very  prominent  position  in 
pathological  circles. 

White  blood-corpuscles  are  classified  in  two  varieties: — 

I.  Lymphocytes  are  without  granules  in  the  cell  and  without 
amoeboid  movement. 

(a)  Small  mononuclear  lymphocytes  are  about  the  size  of  a  red 
blood-corpuscle,  have  a  large,  round,  concentric  nucleus,  a 
small  amount  of  cytoplasm,  and  are  strongly  l)asophilic,  20 
per  cent. 


172  PHYSTOLOnY. 

(h)  Large  mononuclear  lymphocytes  have  a  large,  oval  nucleus, 
located    excentrically ;      cytoplasm     relatively    considerable, 
not  granular,  and  are  weakly  basophilic,  1  per  cent. 
II.  Leucocytes  have  a  granuhir  cytoplasm  and  amoeboid  move- 
ment. 

(a)  Transitional  are  mononuclear  leucocytes,  having  a  large 
nucleus,  considerable  granular  cytoplasm,  and  neutrophilic 
granules.  They  are  a  transitional  form  between  the  large 
lymphocytes  and  the  polymorphonuclear  leucocytes,  7  per 
cent. 

(h)  Polymorphonuclear  leucocytes  have  the  amoeboid  movement 
well  developed;  the  granules  in  the  cytoplasm  are  neutro- 
philic; and  the  nucleus  is  divided  into  lobes,  connected  by 
bands. 

(c)  Eosinophiles  have  a  segmented  nucleus,  the  granules  in  the 
cy toplasjn  are  large  and  stain  with  eosin ;  they  are  oxyphilic, 

(d)  Mast  cells  are  small  in  number,  with  a  polymorphic  nucleus 

and  basophilic  granules. 

Amoeboid  Movement. — All  the  leucocytes  have  in  common  a  very 
remarkable  attribute  of  spontaneously  changing  their  shape  and 
thereby  executing  certain  movements,  which,  from  their  great 
similarity  to  those  performed  by  the  micro-organism,  amoeba,  have 
been  termed  amoehoid.  When  the  conditions  of  temperature  and 
moisture  are  maintained  at  the  proper  standard,  the  leucocytes  will 
be  seen  slowly  to  alter  their  shapes  and  to  send  out  from  their  cyto- 
plasm little  processes  into  which  the  remainder  of  the  leucocytes 
seem  to  flow,  thereby  causing  a  slight  movement  with  change  of 
position.  This  process  repeated  successively  gives  to  the  cell  its 
power  slowly  to  move  from  place  to  place,  after  having  worked  its 
way  through  the  vessel-walls  into  the  surrounding  connective  tissues. 
This  locomotion  is  frequently  termed  the  "wandering"  of  the  cell. 

To  their  sticky  exteriors  there  are  frequently  seen  adhering 
fine  pieces  of  broken-down  cells,  bacteria,  and  other  foreign  par- 
ticles. By  reason  of  certain  internal  circulatory  movements  in  the 
protoplasm  of  the  leucocytes,  these  adherent  foreign  particles  may 
be  drawn  into  the  interior  of  the  cell,  where  some  are  absorbed,  and 
others  excreted  as  effete  matters. 

Functions  of  the  Leucocytes. — It  is  definitely  known  that  the 
leucocytes  play  an  important  role  in  the  process  of  blood-coagula- 
tion.    Their  relation  to  this  most  important  process  will   be  dis- 


THE  BLOOD.  173 

cussed  under  the  head  of  "Coagulation."     They  are  believed  to  help 
maintain  the  needed  proportion  of  proteids. 

Their  most  evident  function  is  the  protection  of  the  economy 
from  both  harmless  and  pathogenic  bacteria.  This  they  accomplish 
by  two  methods.  The  first  is  by  generating  a  defensive  proteid 
which,  when  imbibed  by  the  bacteria,  kills  them.  The  second  and 
more  usual  method  is  that  of  drawing  into  their  interiors  the  various 
bacteria,  together  with  the  debris  resulting  from  lesions,  and,  as  it 


Fig.  .5.]. — LeiR'ocytes  of  ^lan,  showing  Aina'boid  Movement.      (Landois.) 


were,  eating  them.  From  this  apparent  consumption  of  foreign  par- 
ticles they  have  gained  for  themselves  the  name  of  phagocytes,  and 
the  act  is  known  as  phagocytosis.  The  seat  of  the  presence  of  the 
bacteria  marks  a  miniature  battlefield,  with  the  hosts  of  bacteria 
drawn  up  on  one  side  in  battle  array  against  the  leucocytes,  the  two 
armies  to  become  engaged  in  a  death-struggle.  If  the  leucocytes, 
now  termed  phagocytes,  are  victorious,  they  not  only  kill  their  adver- 
saries, but  even  remove  every  vestige  of  the  combat,  aided  by  the 
fixed  connective-tissue  cells.     Those  leucocytes  which  come  out  of 


174  PHYSIOLOGY. 

the  affray  iinharnicd  and  are  no  longer  needed,  find  their  way  back 
into  the  blood-stream. 

If,  however,  the  bacteria,  with  their  toxic  secretions  and  excre- 
tions, are  too  powerful  for  the  phagocytes,  the  latter  succumb,  to 
become  pus-corpuscles.  When  the  pus  has  been  removed  by  drain- 
age and  the  action  of  other  leucocytes,  the  broken-down  tissues  are 
replaced  by  regenerating  connective  tissues. 

Bacteria  alone  are  not  the  provocation  for  attack  by  the  phago- 
cytes, for  the  presence  of  other  foreign  matters  will  also  call  out  an 
assault.  It  is  well  known  that  surgical  ligatures  of  gut  and  silk 
that  are  allowed  to  remain  wiiliin  the  body-cavity  and  tissues  are 
gradually  removed,  particle  by  particle,  by  the  phagocytic  action  of 
the  leucocytes. 

The  absorption  of  the  tails  of  tadpoles  and  other  batrachians 
is  due  to  phagocytic  action. 

Diapedesis. — By  reason  of  their  locomotive  tendencies  the  leu- 
cocytes and  red  corpuscles  are  able  to  make  their  way  through  the 
walls  of  the  capillaries;  this  emigration  has  been  styled  diapedesis. 
There  are  several  stages  before  the  leucocyte  finally  makes  its  exit, 
namely:  slowing  of  the  current  with  the  adherence  of  the  cell  to 
the  side  of  the  blood-vessel,  and  projection  of  processes,  to  be  fol- 
lowed by  the  gradual  exit  of  the  entire  leucocyte.  This  process 
occurs  to  some  extent  in  health,  but  is  greatly  exaggerated  by 
inflammation,  presence  of  bacteria,  etc.  Circumscribed  collections 
outside  of  the  vessels  often  form  abscesses;  the  leucocytes  then 
receive  the  name  pus-corpuscles.  The  leucocytes  in  this  condition 
usually  are  dead  and  show  signs  of  fatty  degeneration.  Frequently 
red  corpuscles  follow  in  the  wake  of  the  white  ones,  passing  through 
the  openings  in  the  vessel-walls  made  by  the  former. 

In  acute  fevers  and  septic  processes,  as  the  temperature  rises 
there  follows  a  decrease  in  the  number  of  erythrocytes,  with  a  corre- 
sponding increase  of  leucocytes. 

Origin  of  Leucocytes. — The  source  of  the  colorless  corpuscles 
seems  to  be  rather  extended.  They  originate  in  the  bone-marrow 
and  spleen,  but  the  credit  for  greatest  production  belongs  to  the 
lymphoid  tissues  and  lymphatic  glands.  From  these  latter  sources 
the  leucocytes  enter  the  lymph-circulation,  from  thence  to  be 
emptied  into  the  blood-stream.  After  having  once  gained  entrance 
to  the  blood-circulation  there  is  rapid  multiplication  to  keep  up  the 
proper  supply,  since  many  succumb  to  the  poisons  secreted  and 
excreted  by  the  various  bacteria. 


THE  BLOOD. 


175 


Blood-plates  and  Elementary  Granules. — In  addition  to  tlie 
erytlirocytes  and  leucocytes  found  floating  in  the  liquor  sanguinis, 
there  have  been  discovered  other  numerous,  smaller  bodies,  termed 
blood-plates  and  elementary  granules. 

The  blood-plates  are  pale  yellow  or  colorless  discs;  round,  oval, 
or  crescentic  in  shape;  and  varying  within  wide  ranges  as  to  size, 
although  always  smaller  than  red  corpuscles.  In  blood  that  has 
been  drawn  from  the  vessels  they  diminish  very  rapidly  both  in 
numbers  and  size,  becoming  gradually  dissolved  in  the  plasma,  and 
are  believed  to  assist  in  coagulation.     As  to  their  nature,  there  is 


Fig.   54. — Blood-plates  and  their  Derivatives.      (Landois.) 

1,  Red  corpuscle  on  the  flat.  2,  On  the  side.  3,  Unchanged  blood-plates. 
■4,  Lymph-corpuscle  surrounded  by  blood-plates.  5,  Altered  blood-plates.  6, 
Lymph-corpuscle  with  two  heaps  of  blood-plates  and  threads  of  fibrin.  7, 
Group  of  fused  blood-plates.  8,  Small  group  of  partially  dissolved  blood-plates 
with  fibrils  of  fibrin. 


some  diversity  of  opinion,  but  the  consensus  of  thought  seems  to  be 
in  favor  of  the  plates  being  formed  bodies,  and  not  precipitates. 
They  have  been  found  to  contain  the  same  elements  chemically  as 
do  the  nuclei  of  the  leucocytes,  so  that  they  are  probably  fragments 
of  the  nuclei  of  disintegrated  leucocytes.  In  nmnber,  their  range 
is  very  extensive:  from  15,000  to  200,000  in  a  cubic  millimeter  of 
blood.  They  take  part  in  the  formation  of  thrombi  and  in  coagu- 
lation of  blood. 

The  elementary  granules  are  smaller  than  the  blood-plates  and 
appear  to  be  composed  of  portions  of  the  protoplasm  of  leucocytes. 
They  contain  proteid  and  fatty  matters. 


176  PHYSIOLOGY. 

FORMATION  OF  RED  BLOOD=CORPUSCLES. 

The  red  corpuscles,  as  every  other  portion  of  the  economy,  per- 
form their  allotted  task  and  round  of  existence,  to  finally  die  and 
disappear.  Just  how  long  the  red  corpuscle  lives  is  yet  unknown, 
but  that  it  cannot  be  very  long  lived  is  probable  when  we  consider 
that  its  haemoglobin  is  the  parent-body  of  the  bile-pigments  which 
are  constantly  being  expelled  from  the  body  as  portion  of  the  faeces. 
Hence  there  must  constantly  be  manufactured  a  new  supply  of  cor- 
puscles to  replace  those  that  die. 

The  origin  of  the  red  corpuscle  as  to  time  may  be  spoken  of  as 
that  which  occurs  during  intra-uterine  life  and  that  occuring  during 
extra-uterine  life. 

During  Intra-uterine  Life. — The  corpuscles  which  first  appear 
in  the  human  embryo  owe  their  existence  to  a  very  simple  origin. 
They  differ  in  some  resj)ects  from  those  that  appear  later  during 
intra-uterine  life,  and  very  materially  from  those  formed  during 
life  outside  of  the  uterus. 

The  wall  of  the  yelk-sac,  situated  entirely  outside  of  the  body 
of  the  embryo,  is  the  seat  of  the  first  vessels  and  blood.  In  the 
chick  the  corpuscles  appear  during  the  first  days  of  incubation  and 
before  the  appearance  of  a  heart.  At  the  end  of  the  first  day,  sur- 
rounding the  early  embryo  there  appears  a  circular,  vascular  area 
made  up  of  cords  of  cells  in  which  are  developed  the  first  evidences 
of  the  vessels  and  corpuscles.  The  corpuscles  appear  in  groups 
within  this  branched  network  of  mesoblastic  cells,  where  they  f onn 
the  ''blood-islands'^  of  Pander.  Presently  the  cords  of  mesoblastic 
cells  which  compose  this  network  begin  to  become  vacuolated  and 
hollowed  out  to  constitute  a  system  of  branching  canals,  at  the  same 
time  that  their  cells  acquire  the  endothelial  type.  The  small, 
nucleated  masses  of  protoplasm,  known  as  the  "blood-islands," 
undergo  disintegration,  whereby  their  nuclei  are  set  free  soon  to 
collect  around  themselves  a  thin  envelope  of  protoplasm.  These 
constitute  the  primitive  red  corpuscles,  and  are  the  only  bodies  con- 
tained within  the  blood  during  the  first  month.  In  the  meantime 
they  have  been  acquiring  a  reddish  hue,  which  marks  the  advent  of 
the  haemoglobin.  As  the  canals  become  extended  and  branched 
eventually  to  connect  with  the  heart  as  its  system  of  vessels,  there 
appears  within  them  a  fiuid  into  which  are  emptied  the  red  cor- 
puscles. Thus  is  completed  the  circulation.  According  to  Klein, 
the  nuclei  of  the  protoplasmic  vessel-walls  multiply  to  form  new 
cells.     The  primitive  corpuscles  are  spherical  in  shape,  nucleated, 


THE  BLOOD.  I77 

and  possess  amoeboid  movements.  They  undergo  multiplication  by 
karyokinesis. 

During  the  foetal  period  the  protoplasm  of  the  connective-tissue 
corpuscles,  derived  from  the  mesoblast,  contains  ceils  of  the  size  and 
appearance  of  blood-corpuscles.  The  mother-cells  elongate,  throw 
out  processes  which  become  hollowed  out  and  branched  until  they 
reach  the  regular  circulatory  vessels,  with  which  they  unite  to  empty 
into  them  their  fluid  and  cells.  During  this  period  also  they  seem 
to  be  developed  from  the  liver,  spleen^  and  red  bone-marrow. 

During-  Extra-uterine  Life. — For  some  time  after  the  birth  of 
the  mammal,  nonnucleated  corpuscles  are  still  formed  in  the  spleen, 
liver,  and  connective-tissue  cells,  but  by  far  the  most  important  and 
prolific  seat  is  in  the  red  marroiv  of  hones.  It  is  in  the  bones  of  the 
skull,  trunk,  and  ends  of  the  long  bones  that  blood-fonnation  is 
most  extensive,  since  the  shafts  of  these  bones  contain  a  yellow, 
fatty  substance  which  is  nonproductive.  Within  the  marrow  are 
seen  numbers  of  nucleated,  red  cells,  which  are  very  similar  to  the 
corpuscles  of  the  embryo,  and  which,  like  them,  multiply  by  karyo- 
kinesis. From  these  repeated  divisions  there  result  nonnucleated 
red  corpuscles  which  are  washed  into  the  circulation.  The  blood- 
forming  cells  have  received  the  name  of  erythroilasts,  or  hwmato- 
hlasts,  and  are  particularly  numerous  after  copious  ha?morrhage, 
when  the  lost  blood  is  being  replaced  by  more  active  formation.  At 
such  times  some  erythroblasts  may  appear  in  the  blood-stream,  hav- 
ing been  forced  out  prematurely,  so  active  is  the  function  of  the 
red  marrow  in  striving  to  repair  the  damage  done.  These  soon  lose 
their  nuclei  while  in  the  blood-stream.  If  the  loss  by  hsemorrhage 
has  been  particularly  severe,  the  yellow  bone-marrow  and  spleen 
assist  in  blood-manufacture,  for  in  the  latter  and  in  the  splenic  vein 
are  found  nucleated,  red  corpuscles  identical  with  those  of  the  red 
marrow  of  bone. 

DESTRUCTION  OF  THE  RED  CORPUSCLES. 

No  exact  time  can  be  given  as  the  life-period  of  an  erythrocyte, 
but  it  is  usually  estimated  to  be  in  the  neighborhood  of  three  or 
four  weeks.  The  student  can  gain  some  comprehension  of  the  num- 
ber of  corpuscles  which  must  constantly  be  undergoing  disintegra- 
tion when  he  recalls  the  fact  that  all  of  the  pigmentary  matters  in 
the  body  owe  their  existence,  directly  or  indirectly,  to  the  haemo- 
globin of  these  little  bodies.  The  quantities  of  urinary  and  biliary 
pigments  alone  that  are  excreted  from  the  economy  are  considerable. 

12 


178 


PHYSIOLOGY. 


Physiologists  have  proved  that  there  are  fewer  red  corpuscles 
in  the  hepatic  than  in  the  portal  vein.  The  bile-pigments  are 
formed  by  the  liver-cells;  these  coloring  matters  contain  only  traces 


Fig.   55. — Blood-crystals  of  Man  and  Dilleieiit  Animals.      (Tuan- 
HOFFEB  and  Frey.) 

1,  Hsemoglobia  crystals:  Mo,  squirrel;  Tr,  guinea-pig;  M,  groundmole; 
L,  Horse;  Em,  man;  H,  Marmot;  Ma,  cat;  T,  cow;  mv,  from  venous 
blood  of  a  cat.  2,  Hsematin  crystals;  E,  man;  Vb,  sparrow;  M,  cat. 
3,    Haematoidin  crystals  from  an  old   extravasation  of  blood  in   man. 

of  iron,  while  the  hepatic  cells  are  rich  with  it.  They  give  the  char- 
acteristic test  for.  iron  when  treated  with  hydrochloric  acid  and 
potassium  f  errocyanide. 


THE  BLOOD.  179 

Only  traces  of  the  iron  are  excreted  as  a  constituent  of  the  bile. 
The  presence  of  iron  in  the  spleen  has  long  made  this  organ  seem 
a  cradle  to  many  physiologists  where  erythrocytes  are  born  and  nour- 
ished. But  the  presence  of  this  same  element  advances  an  argu- 
ment equally  as  strong  in  favor  of  the  spleen  being  the  grave  for 
these  same  little  bodies. 

Pathologically,  masses  of  iron  substances  are  found  within  the 
spleen,  liver,  and  red  bone-marrow  when  aljnormal  disintegration 
occurs,  as  in  anwmia. 

CHEMISTRY  OF  THE  CORPUSCLES. 

The  red  corpuscles  consist  of  a  stroma  containing  in  its  meshes 
a  peculiar  proteid  haemoglobin.  Chemically  they  are  made  of  60  per 
cent,  of  water  and  36  per  cent,  of  haemoglobin,  the  remaining  -f  per 
cent,  representing  the  stroma,  which  is  made  up  of  lecithin,  choles- 
terin,  and  nulceo-proteid.  The  white  corpuscles  consist  of  solids 
and  water.  The  solids  are  gluco-proteids  and  nucleo-proteids  and  a 
small  amount  of  albumin  and  globulin.  The  protoplasm  may  also 
contain  glycogen  and  fat.  The  nuxileus  is  made  up  of  nucleo-pro- 
teids, nuclein,  and  nucleic  acid.  The  phosphorus  content  of  the 
nucleus  is  greater  than  that  of  the  protoplasm. 

The  table  on  page  180  is  the  result  of  the  analyses  reported  by 
Halliburton. 

The  other  named  constituents  are  common  to  the  two  kinds  of 
corpuscles.  The  mineral  components  are  principally  the  chlorides 
of  potassium  and  sodium  and  the  phosphates  of  calcium  and  mag- 
nesium, the  phosphates  being  in  greater  proportion.  Water  forms 
90 "per  cent,  of  the  corpuscular  contents.  It  will  be  remembered 
that  the  sodium  salts  assume  greater  proportions  in  the  plasma. 
The  nucleo-proteid  obtained  from  the  white  corpuscles  is  the  pre- 
cursor of  the  fibrin-ferment  of  coagulation.  It  is  believed  that  the 
proteid  is  converted  into  fibrin-ferment  through  the  activity  of  the 
calcium  salts  of  the  plasma. 

Haemoglobin. — This  is  the  pigment  matter  of  the  red  corpuscles. 
Haemoglobin  is  a  proteid  composed  of  globin,  a  histon.  and  haematin. 
Its  principal  characteristics  are :  (1)  its  ability  to  combine  chem- 
ically with  oxygen  and  other  gases,  (3)  its  spectroscopic  phenomena, 
(3)  its  crystallization,  and  (4)  the  fact  of  its  containing  iron. 

It  is  by  virtue  of  the  presence  of  this  haemoglobin  that  the  red 
corpuscles  are  capable  of  performing  the  function  of  oxygen-carry- 
ing— carrying  it  from  the  external  respiration  in  the  lungs  to  the 


180 


PHYSIOLOGY. 


Chemicai 

Composition   of   Blood. 

PLASMA. 

'  "Wat.pr 

.    .    90.29% 

vv  diuci        ......••...•• 

'  Serum- 

Average,  52% 
Maximum,  56.7% 
Minimum,  45.6% 
Take  100  parts 

'    Organic 

(8.86%)^ 

^  Proteids   < 

albumin 
Serum-    | 
globulin 
.  Fibrin     . 

.      7.9  % 
0.4  % 

^  Extractives  :     Fats,  etc. 

.      0.56% 

Solids 
l-  C9-'71%)' 

Soluble 

salts  .   ^ 

'  NaCl 
KCl 
NaHCOg 

Inorganic  ^ 

.   (0.85%) 

Na^HPO, 

0.85% 

Insoluble  J  CaHPO, 

salts       1   CaSO, 

. 

V. 

Average, 

48% 
Maximum, 

54.4% 

Minimum, 

43.3% 

Take  100 

parts 


100.00% 
C0EPUSCLE3. 

Water 68.80% 


Solids 

(31.2%) 


Organic 

(30.4%)  ' 


Proteids 

(29.79%) 


Fats 


rHiBmoglobinfHaematin] 

<-^«'  1o,i"l|-  ■  "•"^" 

Globulin 2.43% 

°      I 0.61% 

;erinj 


f  Lecithi 
\Cholesteri 


Inorganic 

(0.8%) 


KCl 

NaCl 

MaCl^ 

CaHPO^ 

Mg3(P0,),. 

Fe  (see  Haematin). 


0.80% 


100.00% 


internal  respiration  in  the  cells  of  the  tissues.  The  liEemoglobin 
molecule  possesses  the  property  of  linking  to  itself  an  oxygen  mole- 
cule, forming  a  compound  known  as  oxylicBmogloUn.  The  union  of 
the  two  molecules  is  so  unstable  that  the  presence  of  an  easily 
oxidized  body,  or  of  an  atmosphere  with  a  lower  oxygen  pressure, 
separates  the  two,  the  oxidizable  body  and  the  atmosphere  taking 


THE  BLOOD.  181 

up  the  oxygen.  Oxyhasmoglobin,  minus  oxygen,  is  usually  termed 
reduced  hoimoglobin;  better,  however,  simply  hasmoglobin.  Oxy- 
htemoglobin  is  most  abundant  in  arterial  blood;  that  is,  blood  that 
has  received  its  oxygen  from  the  lungs  during  respiration  and  is 
then  on  its  way  to  supply  the  needs  of  the  cells  of  the  tissues.  Oxy- 
hsemoglobin  behaves  as  an  acid.  Ordinary  venous  blood,  upon  expo- 
sure to  the  air  for  a  considerable  length  of  time,  becomes  bright  red 
because  of  the  union  of  the  oxygen  of  the  air  with  the  hemoglobin 
of  the  blood. 

Crystallization  of  Haemoglobin. — The  haemoglobin  is  contained 
M'ithin  the  stroma  of  the  corpuscles.  In  form,  the  crystals  of  the 
blood  of  man  and  of  the  great  majority  of  animals  is  that  of  rhombic 


0    »      /  " 


Fig.  56. — Teichmann's  Hsemin-crystals.     (Lahousse.) 

prisms  or  needles  which  belong  to  the  rhombic  system;  in  the 
squirrel  there  are  produced  six-sided  plates. 

Haemoglobin  crystals  are  readily  broken  up  by  the  addition  of 
an  acid  or  an  alkali  into  two  parts:  hcematin  and  globin.  Hcematin 
is  a  brown  pigment,  representing  the  cleavage  product  of  haemo- 
globin in  the  presence  of  oxygen.  It  contains  all  of  the  iron  of  the 
decomposed  crystals,  and  is  not  crystallizable.  In  addition  to  the 
iron,  it  contains  the  four  chief  elements  of  proteid  bodies:  carbon, 
hydrogen,  oxygen,  and  nitrogen.  Globin  is  the  proteid  element  of 
the  liEemoglobin.  It  contains  all  the  sulphur,  and  constitutes  the 
major  proportion  of  the  haemoglobin  luolecule,  which  is  16,000  times 
heavier  than  a  molecule  of  hydrogen. 

Haemin. — Hasmin  is  the  decomposition-product  that  results  from 
the  action  of  hydrochloric  acid  upon  haematin.  The  haemin  crystals 
are  small  rhombic  plates  and  prisms.  The  finding  of  the  crystals 
of  Teichmann  constitutes  the  best-known  clinical  test  for  the  detec- 
tion of  blood.     The  crystals  are  prepared  by  adding  a  small  crystal 


182 


PHYSIOLOGY. 


of  common  salt  to  dry  blood  on  a  glass  slide,  and  then  an  excess  of 
glacial  acetic  acid.  The  preparation  is  then  gently  heated  vintii 
bubbles  of  gas  are  given  off.  Upon  cooling,  the  characteristic 
hsemin  crystals  are  formed.  By  transmitted  light  the  crystals 
appear  as  mahogany-brown,  but  by  reflected  light  they  are  bluish 
black. 


Fig.   57. — Sorby-Biowning  Microspectroseope. 

Chemical  Properties. — Hsemin  crystals  are  insoluble  in  water, 
alcohol,  ether,  and  chloroform.  Very  strong  sulphuric  acid  is 
capable  of  dissolving  them.  Should  this  solution  be  evaporated  to 
dryness  and  the  residue  properly  treated,  there  will  be  produced  a 
brown,  amorphous  powder.  This  product  is  known  as  hcEmatopor- 
phyrin. 

Haematoporphyrin  is  iron-free  htematin.  It  is  frequently  found 
in  pathological  urines,  while  traces  of  it  are  to  be  found  in  normal 
urine. 


THE  BLOOD.  Ig3 

It  has  the  same  formula  as  bilirubin,  isomeric,  but  not  identical. 
Mesoporphyrin,  containing  one  atom  of  oxygen  less  than  hsemato- 
porphyrin,  is  said  to  be  identical  with  hasmatoidin. 

Chlorophyll,  the  pigment  of  plants  concerned  in  respiration  and 
containing  iron,  gives  a  body,  phylloporphyrin,  on  cleavage  by  acids. 
It  is  similar  to  hsmatoporphyrin. 

Haematoidin. — In  old  blood-extravasates  in  the  brain,  hgema- 
toidin  is  found  in  crystals.  It  is  an  iron-free  derivative  of  hgemo- 
globin,  identical  with  bilirubin. 

Methaemoglobin. — Methsmoglobin  is  prepared  chemically  by 
adding  amyl  nitrite  to  blood.  It  contains  the  same  amount  of  oxy- 
gen as  haemoglobin,  but,  owing  to  its  different  combination,  the 
oxygen  cannot  be  removed  even  in  a  vacuum;  hence  it  cannot  be  a 
transporter  of  oxygen  to  the  tissues.  Potassium  chlorate  and  the 
continued  use  of  antipyrin  and  acetanilid  will  produce  methsemo- 
globin. 

Carbon-monoxide  Hsemoglobin,  or  Carboxyhaemoglobin. — With 
carbon-monoxide  gas  (CO)  ha-mogiobin  forms  a  compound  similar  to 
oxyhgemoglobin,  but  known  as  carbon-monoxide  hcemoglohin.  This 
union  is  much  more  stable  than  the  preceding,  so  that  when  carbon- 
monoxide  gas  is  breathed  in  excess  death  results  from  asphyxia,  since 
the  tissues  are  prevented  from  receiving  their  proper  supply  of 
oxygen. 

Carbon-monoxide  results  from  the  incomplete  combustion  of 
carbon  in  coal  and  charcoal  stoves.  Tts  poisonous  properties  are 
caused  by  its  combining  so  strongly  with  the  haemoglobin  of  the 
corpuscles  that  it  prevents  union  with  oxygen,  and  so  produces 
asphyxia.  The  blood  of  both  veins  and  arteries  is  bright,  cherry- 
red  in  color.  In  poisoning  from  this  gas,  artificial  respiration  with 
saline  transfusion  is  sometimes  of  avail. 

For  a  better  understanding  of  the  import  of  the  absorption 
bands  of  the  coloring  matters  in  the  blood,  a  brief  description  will 
be  given  of  the  instrument  whereby  they  are  studied. 

THE  SPECTROSCOPE. 

When  ivliite  light,  or  that  which  reaches  us  from  the  sun,  passes 
from  one  medium  into  another  more  dense,  it  is  decomposed  into 
several  kinds  of  light,  a  phenomenon  to  which  the  name  dispersion 
is  given.  Thus,  when  a  pencil  of  the  sun's  rays  is  passed  through 
a  prism  of  flint  glass,  it  is  broken  up  into  the  seven  colors  of  the 
spectrum.     This  band  of  colors  may  be  seen  naturally  in  the  form 


184 


PHYSIOLOGY. 


of  the  rain'bow.     These  colors  are  violet,  indigo,  blue,  green,  yellow, 
orange,  and  red. 

The  colors  of  the  solar  spectrum  are  not  continuous.  Several 
grades  of  refrangibility  of  rays  are  wanting,  and,  in  consequence, 
throughout  the  whole  extent  of  the  spectrum  there  is  a  great  num- 


THE  BLOOD.  185 

ber  of  very  narrow,  dark  lines  which  run  at  right  angles  to  the  longi- 
tudinal axis  of  this  band  of  light.  They  are  generally  known  as 
Fraunhofer's  lines,  since  the  most  marked  ones  were  first  mapped 
and  indicated  by  him.  They  are  designated  by  the  letters  A,  B,  and 
C,  in  the  red;  D,  in  the  yellow;  E,  h,  and  F,  in  the  green;  G  and  H, 
in  the  violet. 

If  the  light  produced  from  burning  common  salt  (sodium  chlo- 
ride) be  decomposed  by  means  of  a  prism,  it  will  be  found  to  give 
one  broad  yellow  line.  Artificial  light  will  not  give  Fraunhofer's 
lines.  The  D  line  in  the  solar  spectrum  is  due  to  the  volatilizing  of 
the  metal  sodium  in  the  sun.  Other  elements  account  for  the 
remaining  dark  lines  of  the  spectrum. 

The  spectroscope  is  combined  with  the  microscope  when  you 
wish  to  make  a  medico-legal  analysis  of  a  small  amount  of  coloring 
matter  resembling  blood.  The  microspectroscope  used  is  usually  the 
Sorby-Browning. 

As  will  be  seen  from  the  preceding  figure,  it  is  a  very  compact 
piece  of  apparatus,  very  ingenious  in  construction,  and  consists  of 
several  parts.  The  prism  is  contained  in  a  small  tube,  which  can  be 
removed  at  pleasure.  Below  the  prism  is  an  achromatic  eyepiece, 
having  an  adjustable  slit  between  the  two  lenses;  the  upper  lens 
being  furnished  with  a  screw  motion  to  focus  the  slit.  A  side  slit, 
capable  of  adjustment,  admits,  when  required,  a  second  beam  of 
light  from  any  object  whose  spectrum  it  is  desired  to  compare  with 
that  of  the  object  placed  on  the  stage  of  the  microscope.  This 
second  beam  of  light  strikes  against  a  very  small  prism  suitably 
placed  inside  the  apparatus,  and  is  reflected  up  through  the  com- 
pound prism,  forming  a  spectrum  in  the  same  field  with  that 
obtained  from  the  object  on  the  stage. 

^  is  a  brass  tube  carrying  the  compound  direct-vision  prism, 
and  has  a  sliding  arrangement  for  roughly  focusing.  B,  a  milled 
head,  with  screw  motion  to  adjust  finally  the  focus  of  the  achro- 
matic eyelens.  C,  milled  head,  with  screw  motion  to  open  and  shut 
slit  vertically.  Another  screw,  H,  at  right  angles  to  C,  regulates 
the  slit  horizontally.  This  screw  has  a  larger  head,  and  when  once 
recognized  cannot  be  mistaken  for  the  other.  D,  D,  an  apparatus 
for  holding  a  small  tube,  that  the  spectrum  given  by  its  contents 
may  be  compared  with  that  from  any  other  object  on  the  stage. 
E,  A,  screw  opening  and  shutting  a  slit  to  admit  the  quantity  of 
light  required  to  form  the  second  spectrum.  Light  entering  the 
aperture  near  E  strikes  against  the  right-angled  prism  which  I  have 


186  PHYSIOLOGY. 

mentioned  as  being  placed  inside  the  apparatus  and  is  reflected  up 
through  the  slit  belonging  to  the  compound  prism.  If  any  incan- 
descent object  is  placed  in  a  suitable  position  with  reference  to  the 
aperture  its  spectrum  will  be  obtained  and  will  be  seen  on  looking 
through  it.  F  shows  the  position  of  the  field-lens  of  the  eyepiece, 
(r  is  a  tube  made  to  fit  the  microscope  to  which  the  instrument  is 
applied.  To  use  this  instrument,  insert  G  like  an  eyepiece  in  the 
microscope  tube,  taking  care  that  the  slit  at  the  top  of  the  eyepiece 
is  in  the  same  direction  as  the  slit  below  the  prism.  Screw  on  to 
the  microscope  the  object-glass  required  and  place  the  object  whose 
spectrum  is  to  be  viewed  on  the  stage.  Illuminate  with  stage  mirror 
if  transparent.  Remove  A  and  open  the  slit  by  means  of  the  milled 
head  H  at  right  angles  to  D,  D.  When  the  slit  is  sufficiently  open 
the  rest  of  the  apparatus  acts  like  an  ordinary  eyepiece,  and  any 
object  can  be  focused  in  the  usual  way.  Having  focused  the  object, 
replace  A  and  gradually  close  the  slit  till  a  good  spectrum  is 
obtained.  The  spectrum  will  be  much  improved  by  throwing  the 
object  a  little  out  of  focus.  Every  part  of  the  spectrum  differs  a 
little  from  adjacent  parts  in  refrangibility,  and  delicate  bands  or 
lines  can  only  be  brought  out  by  accurately  focusing  their  own  parts 
of  the  spectrum.  This  can  be  done  by  the  milled  head  B.  When 
spectra  of  very  small  objects  are  viewed,  powers  of  V2  ™ch  to  V^o 
may  be  employed. 

These  bands  represent  the  light  absorbed  by  the  colored  medium. 
For  the  same  substance  the  bands  are  always  identical  and  similarly 
placed.  Thus,  a  solution  of  oxyhaemoglobin  of  a  certain  strength 
gives  two  bands,  reduced  hsemoglobin  gives  only  one.  The  other 
derivatives,  methjemoglobin,  haematin,  hgemin,  etc.,  though  similar 
to  haemoglobin  when  viewed  with  the  naked  eye,  yet  each  gives  char- 
acteristic absorption  bands  in  various  positions. 

Hsemochromogen  is  produced  by  treating  an  alkaline  haematin 
solution  with  ammonium  sulphide.     It  is  reduced  alkaline  haematin. 

Carbon-monoxide  haemoglobin,  oxyhemoglobin,  haemochromo- 
gen,  and  haematoijorphyrin  all  have  two  characteristic  bands  in  their 
spectra. 

By  adding  ammonium  sulphide  you  can  distinguish  between 
oxyhaemoglobin  and  carbon-monoxide  haemoglobin,  since  the  two 
bands  of  oxyhaemoglobin  disappear,  whilst  those  of  carboxyhaemo- 
globin  remain  unaltered. 

Haemochromogen  bands  are  to  the  violet  side  and  ha&matopor- 
phyrin  to  the  red  side  of  the  bands  of  oxyhsemoglobin  in  the  spec- 


THE  BLOOD.  187 

tram.  Acid  haematin,  alkaline  haematin,  reduced  haemoglobin,  and 
methgenioglobin  can  each  produce  a  band  on  the  red  side  of  the  D  line. 
A  reducing  agent  makes  this  band  vanish  in  the  case  of  methsemoglobin 
or  alkaline  hgematin,  and  produces  reduced  hsemoglobin  or  reduced 
haematin.  Eeduced  haemoglobin  can  be  temporarily  reoxidized  by 
shaking  the  solution. 

Picro-carmine  gives  a  two-banded  spectrum,  but  it  differs  in 
position  from  the  double  bands  of  oxyhemoglobin.  They  are  unal- 
tered by  ammonium  sulphide,  whilst  oxyhtemoglobin  gives  the  dou- 
ble band  of  reduced  hajmatin  by  the  addition  of  ammonium  sulphide. 

The  amount  of  hsemoglobin  as  calculated  by  various  methods 
and  instruments  has  been  found  to  be  in  man,  13.77  per  cent.;  in 
woman,  12.59  per  cent.  Pregnancy  reduces  the  quantity  from  9  to 
12  per  cent.  Normally  there  are  two  periods  in  a  person's  life  when 
the  amount  of  htemoglobin  attains  maximum  limits — in  the  blood 
of  the  newborn  and  again  between  the  years  twenty-one  and  forty- 
five.  Pathologically  there  follows  a  decrease  during  recovery  from 
febrile  conditions,  as  also  occurs  during  phthisis,  cancer,  cardiac 
disease,  chlorosis,  anaemia,  etc. 

It  is  known  that  dry  haemoglobin  contains  0.4  per  cent,  of  iron, 
and  that  all  the  iron  of  the  blood  is  held  by  the  haemoglobin  of  the 
red  corpuscles.     The  amount  of  iron  in  the  blood  is  about  -iS  grains. 

Colorimetric  methods  consist  in  making  comparisons  between  a 
standard  solution  of  a  known  strength  and  the  test  solution  of  blood 
to  be  examined,  water  being  added  to  the  latter  until  the  exact  shade 
of  the  standard  solution  is  obtained. 

Von  Fleischl's  Haemometer. — This  instrument  consists  of  A,  a 
cylindrical  cell  for  holding  the  prepared  blood;  D,  a  graduated 
wedge-shaped  piece  of  colored  glass  with  which  to  compare  the  solu- 
tion of  blood;  H,  a  stand  with  a  rack  and  pinion;  and  a  capillary 
tube  for  measuring  the  quantity  of  blood  required. 

1.  The  cell  (.4)  is  a  cylindrical  metallic  chamber  divided  by  a 
fixed  partition  into  two  equal  compartments,  open  at  the  top,  but 
closed  at  the  bottom  by  a  base  of  glass.  One  of  these  compartments 
is  to  be  filled  with  distilled  water,  the  other  with  the  proper  quan- 
tity of  blood  dissolved  in  distilled  water. 

2.  The  colored  glass  wedge  {B)  is  fitted  to  a  metal  frame,  so 
that  it  can  be  adjusted  in  the  stand  and  moved  from  side  to  side 
by  the  rack  and  pinion.  When  in  position  the  glass  wedge  moves 
directly  beneath  that  part  of  the  cell  which  contains  the  distilled 
water,  thus  enabling  one  to  compare  the  color  of  the  glass  with  that 


188  PHYSIOLOGY. 

of  the  dissolved  blood  which  fills  the  adjoining  compartment  of  the 
cell.  The  wedge  is  graduated  at  E  from  1  to  100,  the  figures  repre- 
senting the  percentage  of  hgenioglobin  in  the  specimen  of  blood  as 
compared  to  normal  blood  containing  13.7  per  cent,  of  haemoglobin. 

3.  Besides  the  support  for  the  glass  wedge  and  frame,  there  is 
a  white  plaster  mirror  (M)  which  furnishes  the  diffused  light 
required  in  the  test. 

4.  The  capillary  tubes  are  carefully  prepared  to  hold  the  pro- 
per quantity  of  blood.  The  size  of  these  tubes  varies,  and  on  the 
handle  of  each  is  stamped  a  number  indicating  its  capacity.^ 


59. — Von  Fleischl  Hsemometer,     (Lahousse.) 


A,  Mixing  vessel  with  two  compartments:  B,  for  diluted  blood;  C,  for 
pure  water,  reposes  over  the  colored  prism  of  glass.  D.  E,  Scale  to  read  off 
amount  of  haemoglobin.  M,  A  mirror  to  reflect  light.  H,  Milled  wheel  that 
moves  D. 

PHYSICAL  PROPERTIES  OF  THE  PLASMA. 

Plasma  is  the  fluid  part  of  the  blood  as  it  occurs  in  a  healthy 
condition  within  the  circulatory  system.  However,  upon  its  removal 
from  the  body  there  is  formed  in  it  a  solid  substance,  called  fibrin, 
from  elements  which  it  previously  held  in  solution.  The  fluid 
which  surrounds  the  clot  is  termed  serum;  it  is  plasma  minus  fibrin. 
Plasma  is  described  as  a  clear,  somewhat  viscid  fluid;  that  of  man, 
when  strata  are  examined,  is  colorless;  when  in  bulk  it  is  slightly 
yellow  because  of  the  presence  of  a  pigment. 


^  Dare's  hsemoglobinometer  is  most  frequently  employed. 


THE  BLOOD.  189 

CHEMICAL  PROPERTIES  OF  PLASMA  AND  SERUM. 

In  order  to  examine  plasma,  a  very  great  amount  of  caution  is 
necessary  to  prevent  its  coagulation,  even  after  separating  the  cor- 
puscles. The  most  common  methods  for  obtaining  it  in  a  liquid 
state  are  by  the  use  of  the  "living  test-tube" — an  excised  piece  of 
jugular  of  a  horse  filled  with  blood,  and  cold  as  an  environment.  It 
has  been  found  that  serum  differs  from  plasma  only  in  respect  to 
certain  proteids,  and,  as  it  is  so  much  easier  to  handle  the  serum, 
the  latter  is  principally  used  for  experimentation. 

Chemically  the  plasma  is  composed  of  inorganic  and  organic 
substances,  with  certain  gases. 


In  Weight.  In  Volume. 

Fig.   60. — Relative  Proportion  of   Corpuscles  and  of   Plasma.      (Human 
Blood.)      (Laxglois.) 

Inorganic  Constituents. — The  plasma's  greatest  factor  is  water. 
It  is  this  which  gives  it  fluidity  and  is  present  to  the  extent  of  90 
per  cent.  There  are  present  many  salts :  sodium  chloride,  carbonate 
of  soda,  chloride  of  potassium,  sulphate  of  potassium,  phosphate  of 
calcium,  phosphate  of  sodium,  and  phosphate  of  magnesium.  The 
first  two  occur  in  the  greatest  amounts,  the  remaining  ones  only 
as  traces.  It  is  carbonate  of  soda  that  gives  to  plasma  its  ability 
to  absorb  carbonic  acid  and  it  also  contributes  much  to  its  alkalinity. 

Organic  Constituents. — These  components  are  readily  divisible 
into  profeid  and  nonproteid  groups. 

The  Proteids  are: — 

1.  One  albumin  (serum-albumin). 

2.  Two  globulins,  termed  serum-globulin  and  fibrinogen. 

3.  A  nucleo-proteid. 

The  classes  of  proteids  present  various  soIubilHies  in  neutral  salt 
solutions,  by  appreciation  of  which  they  are  able  to  be  separated 
from  one  another. 


190  PHYSIOLOGY. 

The  albumins  upon  liali'-iBatiiration  with  ammonium  sulphate 
remain  in  solution,  while  the  globulins  and  nucleo-proteids  are  pre- 
cipitated. The  precipitate  is  removed  by  filtrations,  or  the  albu- 
mins may  themselves  be  precipitated  by  saturation  with  ammonium 
sulphate. 

The  gluhuUns  almost  universally  possess  the  characteristic  of 
coagulating  when  heat  of  75°  C.  is  applied  to  them.  In  man  the 
globulins  make  up  about  3  per  cent,  of  the  total  serum. 

Fibrinogen  is  also  a  globulin.  It  is  precipitated  by  half -satura- 
tion with  NaCl  thus  making  its  differentiation  from  serum-globulin 
a  comparatively  easy  task.  Upon  precipitating  with  NaCl,  if  a  lime 
salt  be  added,  the  precipitate  partakes  of  the  nature  of  a  fibrin-clot 
or  coagulum,  but  it  is  not  true  fibrin,  since  it  is  a  combination  of 
fibrinogen  with  lime. 

Nudeo-proteid  of  Plasma. — About  the  only  characteristic  that 
is  known  in  connection  with  the  nucleo-proteid  is  that  it  is  very 
essential  to  the  formation  of  fibrin  during  coagulation.  It  is  formed 
by  the  dissolution  of  the  leucocytes  and  blood-plates  after  the  blood 
is  shed  from  the  body.  When  hydrocele,  pericardial,  and  ascitic 
fluids  contain  no  leucocytes,  it  has  been  noticed  that  they  lack  power 
of  spontaneous  coagulation.  The  nucleo-proteids  in  the  presence  of 
calcium  salts  form  a  substance  which  is  identical  in  every  respect 
with  the  fibrin-ferment  of  Alexander  Schmidt.  This  new  substance 
possesses  the  power  of  converting  fibrinogen  into  fibrin. 

The  Nonpkoteids  of  the  Plasma. — The  nonproteids  comprise 
both  nitrogenous  and  nonnitrogenous  elements. 

The  nonnitrogenous  consist  of  carbohydrates  and  fats,  with  small 
amounts  of  lipochrome  and  sarco-lactic  acid. 

The  nitrogenous  elements  comprise  in  their  category  urea,  uric 
acid,  hippuric  acid,  creatin,  and  some  ferments. 

Urea,  which  represents  the  end-product  of  nitrogenous  combus- 
tion of  either  the  tissues  or  the  blood  itself,  and  which  must  be 
included  among  the  normal  elements  of  this  fiuid,  is  found  in  the 
blood  in  small  proportion.  But  it  can  accumulate  in  an  abnormal 
manner  within  the  blood  and  give  rise  to  the  disorder  known  as 
uraemia.  It  is  in  this  way  that  ablation  of  the  kidneys,  acute 
nephritis,  and  the  terminal  feverish  period  of  cholera,  in  which  the ' 
urinary  secretion  is  suppressed,  provoke  the  accumulation  of  urea  in 
the  blood. 

Uric  acid,  which  is  regarded  as  the  product  of  a  work  of  com- 
bustion less  advanced  than  for  urea,  doubtless  owes  its  existence  to 


THE  BLOOD. 


191 


an  incomplete  oxidation  of  the  true,  immediate  principles  of  the 
muscles.  It  may  occur  in  greater  proportion  than  usual  in  combina- 
tion with  soda,  with  the  urea,  in  the  blood  of  gouty  persons,  and  in 
that  of  albuminuric  persons. 

Gases  of  the  Plasma. — Present  knowledge  affirms  the  presence 
of  oxygen,  nitrogen,  and  carbonic  anhydride.  The  first  two  are 
simply  dissolved  in  the  plasma,  but  the  carbonic  anhydride  occurs  in 
from  43  to  57  volumes,  and  then  combines  chemically  with  soda  to 
form  carbonates  and  bicarbonates. 


Fig.   61. — Delicate  Fibrin  Coagiilum    (from   Croupous  Pneumonia.) 
X  350.      (Lenhaetz.) 


COAGULATION   OF  THE   BLOOD. 

Normal  blood  contained  within  the  body  vessels  is  a  fluid.  For 
a  very  brief  period  after  it  makes  its  exit  from  a  wounded  vessel  it 
remains  in  a  liquid  state,  but  mthin  two  or  three  minutes  its  vis- 
cidity increases  until  there  is  formed  a  solid  of  the  consistency  of 
jelly;  to  this  has  been  given  the  name  blood-clot.  The  process 
whereby  the  clot  is  formed  is  termed  coaguJaMon,  and  is  caused  by 
the  presence  of  a  body  called  fihri?i. 

To  best  observe  the  process  of  coagulation,  the  blood  is  drawn 
into  an  open  vessel  as  a  beaker,  care  being  taken  that  the  atmos- 
pheric and  other  conditions  are  favorable.  The  initial  change,  which 
occurs  within  the  first  two  or  three  minutes,  is  the  formation  of  a 
jellylike  layer  over  the  surface  of  the  blood ;  during  the  next  three 
or  four  minutes  this  layer  extends  to  such  a  degree  that  the  entire 


192  PHYSIOLOGY. 

blood-mass  becomes  enveloped.  If  at  this  time  the  contents  of  the 
vessel  be  turned  out,  they  f  onn  a  mold  of  the  exact  shape  of  the  con- 
taining vessel,  or  the  vessel  may  be  inverted  without  the  escape  of 
the  contents.  This  jellylike  mass  is  the  clot.  Within  it  are  impri- 
soned the  serum  and  corpuscles. 

A  straw-colored  fluid,  the  serum,  is  expressed,  appearing  upon 
the  surface  to  form  finally  a  transparent  layer  of  liquid  around  the 
clot.  The  retraction  is  complete  at  the  end  of  from  twelve  to 
twenty  hours,  at  which  time  all  of  the  serum  has  been  expressed  and 
the  corpuscles  enmeshed  within  the  network  of  fibrin.  The  clot,  so 
dense  that  it  may  readily  be  cut  with  a  knife,  being  heavier  than 
the  serum,  is  found  at  the  bottom  of  the  vessel.  It  is  now  just  about 
one-half  of  its  original  size.  The  serum,  when  examined,  is  found 
to  be  practically  free  from  corpuscles.  The  character  of  the  clot 
varies  according  to  the  state  of  the  blood.  It  is  large,  soft,  and 
tears  easily  at  times.  At  other  times  it  is  small,  resistant,  and  from 
the  energetic  contraction  of  the  fibrin  the  edges  of  the  upper  sur- 
face of  the  clot  curve  over  so  as  to  form  a  sort  of  cup. 

The  clotting  of  the  blood  is  due  to  the  development  in  it  of 
fibrin,  whose  fibrils  arrange  themselves  in  the  form  of  a  network. 

In  blood  within  its  vessels  there  are  found  no  such  fibrils  of 
fibrin;  therefore  normally  no  coagulation  occurs  within  the  body. 
These  fibrils  then  must  have  been  formed  by  some  change,  chemical 
or  otherwise,  of  one  or  more  constituents  of  the  blood.  That  the 
corpuscles  themselves  cannot  form  a  clot  excludes  them,  so  that  our 
attention  is  turned  to  the  plasma.  In  it  is  formed  the  fil^rin,  for 
pure  plasma  from  which  the  corpuscles  have  been  removed  very 
readily  coagulates.  When  blood  is  vigorously  beaten  with  twigs, 
long  shreds  of  a  nearly  transparent  substance  are  found  adhering 
to  them.  These  are  fibrin-fibers,  free,  or  nearly  so,  from  corpuscles. 
Its  structure  consists  of  very  delicate,  doubly-refractive  fibrils  of 
microscopical  size. 

Many  theories  have  been  propounded  to  account  for  the  forma- 
tion of  fibrin  and  the  coagulation  of  the  blood,  but  the  one  most 
widely  received  is  that  of  Hammersten,  a  Swedish  investigator. 

In  the  study  of  plasma  it  was  learned  that  one  of  its  constitu- 
ents was  a  proteid  of  the  globulin  class,  to  which  had  been  given  the 
name  fibrinogen.  It  is  held  in  solution  by  the  plasma  and  is 
believed  to  be  an  end-product  of  the  disintegration  of  useless  white 
corpuscles.  Within  the  circulating  fluid  there  is  an  immense  num- 
ber of  these  white  cells;   when  blood  is  withdrawn  from  the  living 


THE  BLOOD. 


193 


vessel  there  is  a  large  and  very  sudden  destruction  of  them;  accord- 
ing to  Alexander  Schmidt,  71.7  per  cent,  are  dissolved.  When  these 
little  bodies  are  disintegrated  in  the  laboratory  they  yield  nucleo- 
proteids ;  so  that  it  is  very  probable  that  practically  the  same  pro- 
ducts result  upon  disintegration  in  the  shed  blood.  To  this  nucleo- 
proteid  has  been  given  the  name  prothrombin.  By  the  action  of  the 
calcium  salts  dissolved  in  the  blood-plasma  the  prothrombin  is  con- 
verted into  fibrin-ferment,  or  thrombin.  When  thrombin  comes  into 
contact  with  the  fibrinogen  molecule  dissolved  in  the  plasma  it  splits 
it  into  two  parts:  one  is  a  globulin,  which  is  very  small  in  propor- 
tion and  equally  unimportant;  it  remains  in  solution.  The  other  is 
the  insoluble  substance  fibrin,  which  entangles  the  corpuscles  and  is 
so  essential  to  the  formation  of  the  blood-clot. 

The  process  of  fibrin-formation  has  been  neatly  tabulated  by 
Dr.  J.  J.  K.  Macleod/  as  follows: — 

Living  blood 


Plasma 


Albumin      Globulin 


Corpuscles 


White 


Red 


Ca  salts  -\-  Prothrombin 


Fibrinogen  +  Fibrin  ferment 


Second  globulin 


Fibrin 


Serum 


Clot 


Dead  blood 


'^  "Practical  Physiologj'." 


13 


19i  PHYSIOLOGY. 

To  epitomize,  it  may  be  said  that  coagulation  depends  upon 
three  factors,  according  to  Hammersten's  theory:  (1)  calcium  salts  to 
convert  the  nucleo-proteids  in  the  form  of  prothrombin  into  throm- 
bin, or  (2)  fibjin- ferment;  this  latter  breaks  up  the  (3)  fibrinogen  in 
solution  into  an  unimportant  globulin  and  the  all-important  fibrin. 

Fibrin-ferment  is  a  term  used  simply  for  convenience  and  prob- 
ably is  a  misnomer.  It  is  a  proteid  of  the  globulin  group  whose  sub- 
stance does  not  seem  to  be  used  up  in  the  process  nor  to  enter  into 
the  fibrin  formed;  a  small  quantity  of  it  serves  to  break  up  an 
immense  amount  of  fibrinogen. 

Morawitz  thinks  that  extracts  of  organs  form  a  proenzyme  from 
a  zymogen  stage,  thrombogen,  whence  thrombin  arises  from  the  pro- 
enzyme under  the  influence  of  the  calcium  ions.  The  formation  of 
thrombin  is  stopped  immediately  by  sodium  fluoride,  and  the  course 
of  formation  of  thrombin  can  be  closely  followed  by  the  addition  of 
small  quantities  of  this  salt. 

In  the  peculiar  hereditary^  disease  of  males  only,  known  as 
haemophilia,  it  sometimes  happens  that  diminished  coagulability  is 
due  to  a  deficiency  of  the  calcium  salts.  Consequently  the  tendency 
to  bleed  may  in  some  cases  l)e  lessened  by  the  internal  administra- 
tion of  calcium  chloride,  or  the  actual  hasmorrhage  may  be  stopped 
upon  its  local  application  or  of  adrenalin. 

A  condition  known  as  biiffy  coat  occurs  when  blood  coagulates 
very  slowly.  It  is  most  readily  seen  in  horses'  blood,  being  caused 
by  the  more  rapid  sinking  of  the  red  corpuscles  in  slow  coagulation, 
thus  leaving  the  upper  stratum  to  consist  of  a  layer  of  fibrin  and 
white  corpuscles.  This  whitish  layer  is  elastic,  has  some  resistance, 
is  more  or  less  opaque,  and  has  therefore  been  designated  the  buffy 
coat. 

The  shape  of  the  vessel  is  also  a  factor  in  the  production'  of 
"buffy  coat."  If  the  vessel  be  long  and  straight,  the  fall  of  the  cor- 
puscles is  facilitated.  The  buffy  coat  then  appears.  No  buffiness, 
however,  is  seen  if  the  vessel  be  large  and  low,  and  if  the  blood  be 
received  in  a  vessel  which  is  shaken  from  time  to  time.  The  blood 
of  different  parts  of  the  vascular  system  shows  differences  as  to  the 
time  required  for  complete  coagulation.  Arterial  blood  coagulates 
more  quickly  than  venous ;  blood  of  the  hepatic  veins  coagulates  very 
little,  and  the  same  is  true  of  menstrual  blood — probably  due  in  the 
latter  to  mixture  with  the  alkaline  vaginal  secretions,  for,  when 
menstruation  is  so  abundant  that  this  alkalinity  is  overcome,  then 
clotting  may  ensue, 


THE  BLOOD.  195 

Certain  conditions  favor  the  rapidity  of  coagulation.  Clotting 
is  accelerated  by  these  factors:  1.  Calcium  salts.  2.  A  tempera- 
ture a  little  higher  than  that  of  the  body  (102°  to  107°  F.).  3.  Pre- 
sence of  foreign  bodies.  If  a  needle  be  made  to  penetrate  the  wall 
of  a  vessel,  fibrin  is  deposited  upon  it  and  so  produces  coagulation. 
It  seems  to  be  a  sort  of  phenomenon  analogous  to  that  which  occurs 
when  a  thread  is  suspended  in  a  solution  of  sugar,  when  the  crystals 
of  sugar  are  deposited  upon  it.  Injections  of  laky  blood,  biliary 
salts,  fibrin-ferment,  and  rapid  venous  injection  of  a  strong  alkaline 
solution  of  a  nucleo-proteid  also  hasten  coagulation.  4.  Injury  to 
the  vessel-walls.  5.  Agitation,  probably  because  there  is  then  a 
more  free  mixture  with  oxygen.  Gelatin  increases  the  coagulating 
power  of  blood,  and  has  been  used  in  haemophilia. 

Coagulation  is  retarded  by:  1.  Oxalates,  which  combine  with 
calcium.  2.  A  very  low  temperature.  3.  The  saturation  of  blood 
with  CO2  (thus  in  asphyxia  the  blood  does  not  coagulate).  4.  Blood 
received  into  a  vessel  filled  with  oil  does  not  coagulate.  5.  Coagula- 
tion is  prevented  when  the  blood  is  in  contact  with  normal,  living, 
vascular  walls.  The  addition  of  certain  articles  retards  coagula- 
tion; thus,  feeble  doses  of  alkalies,  carbonate  of  sodium  and  potas- 
sium, sugar,  water,  albumin,  injection  of  peptone,  and  leech  extract. 
In  the  disease  known  as  haemophilia,  as  well  as  in  lightning  strokes, 
the  blood  does  not  coagulate. 

Why  Blood  does  not  Normally  Coagulate  within  the  Blood-vessels. 
— Much  time  and  experiment  have  been  given  to  ascertaining  the 
cause  for  noncoagulation  within  living  walls,  but  notwithstanding 
the  question  is  yet  unsettled.  By  some  it  is  thought  that  the 
destruction  of  the  white  corpuscles  is  not  extensive  enough  to  fur- 
nish the  proper  supply  of  nucleo-proteid,  from  which  fibrin-ferment 
is  manufactured.  According  to  Schmidt,  the  blood  within  the  liv- 
ing vessels  is  constantly  being  acted  upon  by  two  opposing  influences : 
one  with  a  tendency  to  promote  coagulation,  the  other  to  oppose  it. 
In  health  the  former  never  gains  the  ascendency.  But  perhaps  the 
real  secret  depends  upon  the  intima  being  alive  and  intact. 

Haemorrhage  and  its  Effects. — It  is  common  knowledge  that  a 
very  abundant  loss  of  1)lood  causes  death.  The  blood  has  for  its 
functions  to  insure  the  physical  conditions  of  the  life  of  the  cells 
as  well  as  to  maintain  an  excitability  of  the  nerve-cells  which  gov- 
ern respiration  and  circulation.  Every  considerable  loss  of  blood 
disorders  cell-life  in  the  organism,  tending  to  cause  death.  Necrosis 
very  soon  manifests  itself  when  a  member  has  by  some  procedure 


196  PHYSIOLOGY. 

been  deprived  of  its  normal  supply  of  blood.  When  the  loss  of 
blood  has  been  from  the  whole  system,  and  not  confined  to  any  mem- 
ber, a  general  death  precedes  the  local  death  of  the  cells,  because, 
the  oxygen  not  going  to  the  cardiac  and  respiratory  centers,  the 
functions  of  the  heart  and  lungs  are  arrested.  The  principal  symp- 
toms of  great  loss  of  this  vital  fluid  are  general  paleness  and  lower 
temperature  of  the  cutaneous  surface,  oppression,  breathlessness, 
stoppage  of  the  secretions,  with  finally  general  convulsions  of 
anaemia. 

The  quantity  of  blood  which  can  be  lost  without  causing  death 
varies  according  to  age,  sex,  temperature,  etc.  The  loss  of  some 
cubic  centimeters  in  the  newborn,  of  a  half-pound  in  an  infant  of 
one  year,  or  of  half  the  quantity  of  blood  in  an  adult,  is  capable  of 
causing  death.  Women  bear  the  loss  of  blood  much  better  than 
men  do  because  of  the  periodical  haemorrhages  to  which  they  are 
subject. 

The  renewal  of  the  blood  appears  to  be  accomplished  rapidly, 
although  the  time  of  withdrawal  plays  an  important  role  in  determin- 
ing whether  there  will  l)e  attending  fatality.  If  the  loss  has  not 
been  too  severe,  the  fluid  part  of  the  blood  and  its  dissolved  salts  is 
replenished  by  withdrawal  from  the  lymph  and  plasma  of  the  tissues. 
Later  the  albumin  is  restored,  but  a  much  longer  period  is  required 
for  replenishment  of  the  corpuscles.  The  amount  of  haeonoglobin  is 
diminished  in  proportion  to  the  amount  of  bleeding. 

Shock  very  materially  affects  the  results  of  haemorrhage.  When 
the  sensibilities  are  deadened  temporarily  by  anaesthetics,  less  seri- 
ous results  follow  the  loss  of  a  given  quantity  of  blood  than  do  those 
when  the  same  quantity  escapes  through  accident. 

Transfusion. — This  is  a  process  by  which  blood  is  conveyed 
from  one  animal  to  the  vascular  system  of  another.  It  was  shortly 
after  Harvey's  discovery  of  the  circulation  of  the  blood  that  this 
operation  was  first  practiced  by  Denis,  of  Paris.  He  transfused  with 
success  the  blood  of  a  lamb  into  that  of  a  man.  It  was  believed  that 
a  great  panacea  had  been  discovered  whereby  not  only  blood  lost  by 
haemorrhage  could  be  replaced,  but  a  cure  effected  for  many  diseases 
and  infirmities.  Subsequent  attempts  proved  such  miserable  fail- 
ures that  the  operation  was  abandoned  and  even  proscribed  by  law. 
More  than  a  century  later  it  was  revived,  but  only  after  much  experi- 
mentation upon  the  lower  animals. 

The  serum  of  certain  animals  possesses  the  property  of  dis- 


THE  BLOOD.  197 

solving  the  red  corpuscles  of  another  species  of  animals.  The 
serum  of  a  dog  destroys  the  red  corpuscles  of  man;  the  haemoglobin 
is  dissolved  out.  The  serum,  besides  its  action  on  the  red  corpuscles, 
is  also  active  against  the  white  corpuscles  of  the  same  animal,  stop- 
ping their  amoeboid  movements.  The  globulicidal  action  of  the 
serum  is  related  to  its  poisonous  action  on  microbes.  The  normal 
serum  of  certain  animals  kills  microbes,  as  the  serum  of  the  dog 
kills  the  typhoid  bacilli.  The  power  to  kill  red  corpuscles  and 
microbes  is  due  to  the  presence  in  the  serum  of  a  substance,  an 
alexin.     In  transfusion  this  plays  an  important  part. 

The  knowledge  gained  thereby  was  to  the  effect  that,  for  the 
operation  to  be  at  all  successfully  performed,  blood  of  the  same 
species  of  animal  should  be  used  as  the  one  on  which  it  is  performed. 
It  was  only  after  the  establishment  of  this  rule  that  it  appeared  pos- 
sible to  determine  the  value  of  transfusion  and  to  make  application 
of  it,  with  some  degree  of  safety,  to  man. 

In  practice  there  are  two  kinds  of  transfusion:  (1)  blood  with 
fibrin  ;  (2)  blood  without  fibrin.  In  using  fibrinated  blood  the  stream 
is  passed  directly  from  the  blood-vessel,  either  artery  or  vein,  into 
that  of  the  patient.  Usually  the  peripheral  end  of  a  vein  of  the 
person  furnishing  the  blood  is  united  with  the  central  end  of  a  vein 
of  the  patient.  The  tubing  should  have  been  previously  filled  with 
a  normal  salt  solution  so  as  to  exclude  the  entrance  of  air  into  the 
circulation,  for,  if  sufficient  quantity  of  it  be  introduced,  it  will  be 
carried  to  the  right  side  of  the  heart,  where,  by  virtue  of  the  heart's 
action,  a  froth  will  be  generated,  the  bubbles  from  which,  being 
pumped  into  the  pulmonary  arteries,  arrest  pulmonary  circulation 
and  cause  death.     The  danger  of  coagulation  is,  however,  very  great. 

In  using  defibrinated  blood  the  shed  blood  is  first  whipped  in 
an  open  vessel  with  a  glass  rod  so  as  to  separate  the  fibrin;  it  is  then 
filtered,  heated  to  the  temperature  of  the  body,  and  injected  very 
slowly  into  a  vein  (usually  the  median  basilic)  in  the  direction  of  the 
heart.  Besides  giving  a  tendency  toward  intravascular  coagulation, 
there  is  also  danger  of  introduction  of  bacteria,  whose  entrance  into 
the  injected  blood  occurs  with  the  beating  in  the  process  of  defibrin- 
ation. 

It  has  been  learned  that  the  most  serious  symptoms  of  rapid 
haemorrhage  follow  the  sudden  diminution  in  the  amount  of  blood 
in  circulation,  accompanied  with  a  moderate  fall  of  blood-pressure. 
From  these  data  we  conclude  that  the  proper  measures  to  take  are 


198  PHYSIOLOGY. 

to  replenish  the  amount  of  fluid  regardless  of  the  corpuscles  or  the 
soluble  nutrient  elements  of  the  plasma.  A  precaution  to  be  taken 
is  that  the  fluid  should  be  of  such  a  density  and  nature  that  no  dis- 
turbance in  the  vascular  system  be  generated. 

This  knowledge  has  led  to  the  manufacture  of  various  artificial 
solutions  for  infusion,  the  one  most  used  being  a  warm,  sterilized, 
physiological  salt  solution  (NaCl,  0.95  per  cent.);  this  is  injected 
either  subcutaneously  or  into  any  exposed  vein. 

Transfusion  is  called  for  after  copious  hcemorrhage  (acute  anae- 
mia), or  in  such  cases  of  poisoning  when  the  blood-corpuscles  are 
no  longer  capable  of  supplying  the  tissues  with  their  required  supply 
of  oxygen.  This  condition  is  particularly  prominent  in  carbon- 
monoxide  (CO)  poisoning. 

Plethora. — The  old  physicians  admitted  that  there  was  in  cer- 
tain individuals  of  sanguine  temperament  an  exaggerated  richness 
of  the  mass  of  blood  as  a  consequence  of  too  active  nutrition.  How- 
ever, it  is  impossible  to  verify  in  an  experimental  manner  if  the 
mass  of  blood  be  augmented.  Yet  plethora  is  usually  accompanied 
with  a  swelling  of  the  veins  and  arteries;  an  injection  of  mucous 
membrane;  a  full,  hard  pulse;  congestive  vertigo,  and  dyspnoea  from 
pulmonary  congestion.  Many  physicians  believe  that  there  is  no 
such  condition  as  too  much  blood  in  the  body,  unless  it  be  introduced 
experimentally  by  transfusion.  The  above  symptoms  are  explained 
by  reason  of  an  increased  peripheral  circulation  at  the  expense  of 
the  more  central  one.  Nevertheless,  the  above-named  symptoms 
disappear  by  blood-letting,  which  would  seem  to  admit  the  existence 
of  plethora  to  a  certain  extent. 

An  experimental  plethora  may  be  induced  in  dogs  by  trans- 
fusion; so  that  the  blood  may  be  increased  from  80  to  100  per  cent, 
without  provoking  any  trouble.  The  injected  plasma  is  soon  gotten 
rid  of,  but  the  surplus  corpuscles  remain  for  a  long  time.  There 
is  also  believed  to  be  an  increase  in  the  number  of  red  corpuscles  in 
those  persons  in  whom  for  any  reason  there  should  be  a  suppression 
of  periodically  recurring  haemorrhages,  as  in  menstruation  and  bleed- 
ing from  the  nose. 

Plethora  of  water,  or  liydrcemia,  follows  the  excessive  ingestion 
of  water.  The  condition  is  but  temporary,  however,  as  an  increased 
diuresis  rapidly  eliminates  the  excess  of  water. 

There  is  a  physiological  excess  of  red  corpuscles  in  the  blood  of 
man  and  animals  who  live  in  hio-h  altitudes. 


THE  BLOOD.  199 

MEDICO=LEGAL  TESTS  OF  THE  BLOOD. 

To  determine  that  a  substance  under  examination  and  inspec- 
tion is  blood  several  tests  are  employed : — 

First. — Teichmann's  crystals,  or  hsemin  crystals,  are  a  product 
of  decomposition  of  the  coloring  matter  of  the  blood.  They  may  be 
prepared  by  the  addition  to  the  blood  of  glacial  acetic  acid  and 
sodium  chloride.  A  few  granules  of  dried  blood  with  a  few  granules 
of  salt  are  pulverized  on  a  glass  slide;  having  covered  the  powder 
with  a  glass  circle,  a  drop  of  the  acid  is  allowed  to  flow  under,  when 
the  slide  is  heated.  If  the  examined  substance  be  blood,  the  char- 
acteristic crystals  appear. 

Second. — The  Guaiacum  Test. — On  treating  a  solution  of  the 
coloring  matter  of  the  blood  with  an  alcoholic  tincture  of  guaiacum 
and  an  ethereal  solution  of  hydrogen  peroxide,  a  deep-blue  coloration 
is  produced,  due  to  oxidation  of  the  guaiacum  resin. 

Third. — The  Spectkoscope  Test,  in  which  characteristic  bands 
appear. 

Fourth. — Careful  measurements  of  the  blood-corpuscles,  their 
diameter,  etc.,  by  means  of  the  microscope  and  photomicrographs. 

Fifth. — The  Precipitin  Test. — Strong  rabbits  are  injected 
subeutaneously  with  5  cubic  centimeters  of  sterile  human  blood,  the 
injections  being  repeated  every  two  or  five  days,  depending  upon  the 
condition  of  the  test  animal.  The  occurrence  of  a  rise  of  tempera- 
ture above  101°  F.  or  a  decided  loss  in  weight  are  considered  coun- 
ter-indications to  further  injections  until  after  this  reaction  has  sub- 
sided. It  is  better  to  give  injections  of  only  5  cubic  centimeters 
each  and  always  with  great  care  as  to  asepsis,  since  abscesses  often 
develop  at  or  near  the  site  of  puncture.  Usually  20  to  30  cubic 
centimeters  make  a  sufficient  quantity  for  the  average-sized  rabbit, 
and  with  due  care  a  specific  anti-serum  can  always  be  produced  in 
from  three  to  four  weeks.  After  a  sufficient  quantity  of  blood  has 
been  injected  to  insure  obtaining  an  anti-serum,  the  rabbit  is  chloro- 
formed, the  chest-cavity  opened,  and  the  blood  drawn  from  the  heart 
into  a  sterile  receptacle  by  means  of  a  sterile  trocar  and  cannula. 
The  drawn  blood  is  placed  in  an  icebox  for  one  hour  until  well  coag- 
ulated. Carbolic  acid  is  now  added  to  the  serum,  which  has  separ- 
ated sufficiently  to  make  the  mixture  approximately  0.5  per  cent, 
acid.  The  serum  is  then  drawn  up  into  sterile  pipettes  and  sealed. 
It  will  remain  potent  indefinitely  if  kept  at  a  low  temperature. 


200  PHYSIOLOGY. 

The  test  is  made  as  follows :  A  given  amount  of  the  test-serum 
is  diluted  to  the  desired  extent  with  sterile  water  or  normal  saline 
solution.  To  a  few  cubic  centimeters  of  this  diluted  solution  in  a 
sterile  test-tube  is  added  an  equal  quantity  of  a  similarly  diluted 
solution  of  the  blood  to  be  tested  and  the  tube  left  at  room  tempera- 
ture or  placed  in  an  incubator  for  two  or  three  hours  at  37°  C.  The 
reaction,  if  it  occurs,  will  be  more  rapid  and  marked  if  the  tube  is 
exposed  to  the  higher  temperature.  If  the  dilution  be  sufficient  the 
reaction  will  not  occur  at  room  temperature.  If  the  test-serum  is 
used  undiluted  and  pure  human  blood  is  added  to  it,  the  reaction  is 
immediate. 

If  only  the  sample  of  blood  to  be  tested  is  diluted  and  pure  test- 
serum  is  used,  the  reaction  is  almost  immediate.  The  reaction  is 
marked  by  a  turbidity  of  the  solution,  becoming  constantly  more 
intense.  If  an  old  stain  is  to  be  examined  by  the  serum  test,  the 
material  containing  it  is  washed  in  sterile  water  or  in  sterile  normal 
saline,  the  mixture  is  repeatedly  filtered  and  finally  added  to  some 
of  the  test-serum,  as  in  the  examination  of  fresh  blood  already 
described. 

Contamination  with  monkey  blood  can  be  excluded  first  by  a 
great  dilution  of  the  blood  tested,  and  a  dilution  of  the  test-serum 
of  1  to  500,  with  incubation;  second,  by  a  great  dilution  of  the  blood 
tested,  the  test-serum  being  used  pure  and  the  test  made  at  room 
temperature. 


CHAPTER  VI. 

THE  CIRCULATION. 

In  animals  above  the  very  lowest  grades,  as  also  in  plants,  there 
exists  a  particular  liquid  (nutritive  fluid,  blood,  sap),  which  is  agi- 
tated into  a  circular  or  simply  oscillating  movement.  By  reason 
of  this  movement  it  is  permitted  to  reconstitute  itself  unceasingly,  to 
distribute  the  materials  of  nutrition  to  the  different  parts  of  the  or- 
ganism, and  at  the  same  time  carry  away  some  effete  products. 

In  the  lowest  orders  of  animal  life,  as  the  amoebae  and  infusoria, 
where  no  special  organs  are  manifest  and  no  part  therefore  has  needs 
differing  from  any  other,  there  is  found  no  circulatory  system — no 
heart  or  propelling  body  or  any  blood-vessels.  Its  life  depends  upon 
diffusion  throughout  its  parenchyma  of  substances  brought  from  with- 
out and  of  those  which  must  be  excreted.  It  is  only  as  special  organs 
show  themselves  and  the  liquids  take  determined  directions  toward 
one  or  another  of  them,  that  blood-vessels  are  seen  to  commence; 
these  at  the  same  time  become  the  receptacles  of  products  absorbed  for 
the  purposes  of  nutrition  and  the  distributors  of  these  same  materials 
to  the  various  tissues  of  the  organism. 

It  is,  therefore,  from  complex  organisms  that  the  idea  of  a  per- 
fect circulation  is  gained,  with  its  admirable  mechanism  for  incessant 
movement  whereby  the  fluid  necessary  for  its  growth,  functions,  and 
individual  life  is  forced  to  every  part.  Viewed  as  a  whole,  the  vas- 
cular system  of  the  higher  animals  forms  a  system  of  branching  ves- 
sels or  canals,  closed  in  all  parts,  and  not  showing  at  any  point  in 
their  course  the  least  perceptible  orifice  of  communication  with  the 
external  world.  Consequently,  the  fluids  which  have  to  penetrate  into 
the  closed  channels  of  circulation,  as  well  as  those  which  have  to 
emerge  from  them  for  the  needs  of  secretion  and  nutrition,  only  do 
so  by  passage  through  the  vascular  walls;  that  is,  through  the  finest 
filters  imaginable. 

At  a  variable  point  in  this  tubular  apparatus  there  exists  an 
organ  of  propulsion,  the  heart,  which  is  seconded  in  its  work  by 
auxiliary  means  and  forces  which  aim  to  give  a  determined  and  con- 
stant direction  to  the  movement  of  the  circulatory  fiuid. 

(201) 


202  PHYSIOLOGY. 

In  the  study  of  comparative  anatomy  it  is  found  that  certain 
lower  organisms  are  absolutely  without  any  semblance  of  blood-ves- 
sels, yet  they  absorb  through  the  periphery  of  their  bodies  the  gases  as 
well  as  the  liquids  of  the  fluids  in  which  they  are  plunged,  and,  in  fact, 
are  nourished  and  continue  to  live.  It  is  only  as  animals  with  spe- 
cial organs  appear  in  the  scale  of  animal  life  that  there  is  developed  a 
system  of  canals,  more  or  less  complete,  which  are  intended  to  con- 
tain the  nourishing  fluid.  And  where  there  is  a  circulatory  system 
there  is  present  some  means,  composed — in  the  great  majority  of 
cases — of  muscle,  for  the  impulsion  of  the  circulatory  fluid  to  every 
part  of  the  organism.  Whenever,  in  animal  organisms,  there  is 
transformation  of  energy  into  motion  or  mechanical  work,  it  may 
nearly  always  be  attributed  to  muscle.  So  that  in  the  higher  forms 
of  animals  there  exist  one  or  more  rhythmically  contractile  organs — 
for  the  most  part  muscular  in  nature — to  which  is  attributed  the  task 
of  maintaining  a  definite  circulation. 

Comparative. — Among  insects  and  the  lower  orders  of  Crustacea 
the  heart,  if  such  it  may  be  called,  is  simply  the  contractile  dorsal 
blood-vessel;  among  the  higher  Crustacea,  as  the  lobster,  there  exists 
dorsally  a  well-defined  muscular  sac.  Among  the  invertebrates  in 
general  the  blood  passes  from  the  arteries  into  irregular  spaces, 
known  as  lacunae,  which  are  situated  in  the  tissues  and  from  which 
it  finds  its  way  back  into  the  veins  to  terminate  in  the  heart  for  the 
completion  of  its  cycle.  That  interesting  creature,  the  amphioxus, 
the  lowest  of  the  vertebrates,  possesses  a  primitive,  lacunar  vascular 
system.  Its  contractile  dorsal  vessel  serves  as  its  systemic  heart;  a 
ventral  vessel  serves  as  a  respiratory  heart,  vessels  proceeding  from  it 
to  the  gills.  Fishes  contain  but  a  respiratory  heart,  which  sends 
blood  to  the  gills  for  aeration.  It  consists  of  a  venous  sinus,  an 
auricle,  and  a  ventricle.  From  the  gills  it  finds  its  way  to  the  aorta, 
to  be  distributed  throughout  the  tissues  without  any  further  impul- 
sion. Among  the  amphibians,  as  the  frog,  there  are  found  two  auri- 
cles and  a  single  ventricle.  Eeptiles  possess  two  auricles  with  two 
ventricles,  though  the  latter  are  but  incompletely  separated.  Among 
birds  and  mammals  there  is  a  heart  which  serves  a  double  purpose — 
it  sends  blood  to  the  lungs  for  aeration,  to  the  body  in  general  to 
serve  the  needs  of  its  various  tissues.  The  passage  of  the  blood  to 
the  lungs  is  accomplished  by  the  right  auricle  and  ventricle  and  is 
known  as  the  pulmonary  system.  That  going  to  the  tissues  of  the 
body  is  propelled  by  the  left  auricle  and  ventricle  to  constitute  the 
systemic  system. 


THE  CIRCULATION.  203 

THE   CIRCULATORY    SYSTEM. 

This  system  has  for  its  distinctive  function  the  propulsion  of  the 
blood  to  every  part  of  the  economy.  It  is  a  closed,  vascular  apparatus 
consisting  of  an  impelling  agency,  or  pump,  with  an  outgoing  and 
incoming  system  of  vessels.  The  central  pumping  organ  is  the 
heart,  from  which  proceed  the  vessels  that  carry  the  blood  from  the 
heart  to  the  various  organs  and  parts  of  the  body — the  arteries — and 
the  vessels  returning  the  impoverislied  blood  to  the  right  side  of  the 
heart — the  veins.  Connecting  the  smallest  arterioles  and  the  fine 
radicals  of  the  beginning  veins  is  a  network  of  microscopical  vessels, 
large  enough  in  many  places  to  admit  of  but  a  single  row  of  cor- 
puscles and  whose  walls  are  composed  of  a  single  layer  of  endothelial 
cells;  these  are  the  capillaries. 

THE  HEART. 

The  heart  is  a  hollow,  cone-shaped  organ  of  muscle.  It  is  situ- 
ated in  the  cavity  of  the  thorax,  inclosed  by  a  serous  sac :  the  peri- 
cardium. It  lies  between  the  lungs,  rests  on  the  diaphragm,  and  is 
located  more  on  the  left  than  on  the  right  side.  It  is  placed  obliquely ; 
its  broad  end,  or  base,  by  attachments  to  the  blood-vessels,  is  fixed 
to  the  front  of  the  vertebral  column.  The  base  of  the  heart  extends 
from  the  fourth  to  the  eighth  dorsal  vertebra.  The  apex  is  inclined 
downward,  forward,  and  to  the  left,  where  it  terminates  just  behind 
the  interval  between  the  fifth  and  sixth  ribs,  ^/^  inch  to  the  inner 
side  of  and  ly,  inches  below  the  nipple.  The  heart  is  5  inches  in 
length;  in  breadth,  Sy,  inches;  and  in  thiclmess.  Sy^  inches. 

The  heart  is  brown  in  color,  and  on  its  surface  has  a  longitudinal 
and  a  transverse  groove,  which  shows  a  division  of  the  organ  in  four 
parts :  the  two  auricles  and  two  ventricles.  The  heart  increases  in 
all  dimensions  up  to  a  late  period  in  life,  thus  augmenting  its  weight. 
The  auricles  are  cavities  having  thin  walls.  The  base  of  the  heart 
is  formed  by  the  auricles.  A  partition  separates  them  and  they  are 
connected  with  the  great  veins, — the  cavae  and  pulmonary  veins. — by 
which  they  receive  blood  coming  from  every  portion  of  the  system. 
The  aperture  of  communication  between  the  auricles  and  ventricles  is 
the  auriculo-ventricular  opening,  which  permits  the  blood  to  leave  the 
auricle  to  enter  the  ventricle,  but  valves  prevent  it  from  running  back 
into  the  auricle.  The  thick-walled  parts  of  the  heart  are  the  ven- 
tricles, which  become  thicker  in  the  direction  of  the  apex.  Like  the 
auricles,  they  are  separated  by  a  partition  and  connected  with  the 


204 


PHYSIOLOGY. 


large  arteries, — the  pulmonary  artery  and  aorta, — by  which  they 
send  blood  to  the  entire  system.  Both  ventricles  have  valves  called 
aortic  and  pulmonary,  which  prevent  the  reflow  of  the  blood  from  the 
arteries  into  the  ventricles. 

The  right  auricle  consists  of  an   oblong  part,   the   sinus.     The 
walls  of  the  right  auricle  are  thin  and  translucent,  but  are  thickened 


Fig.   62. — Anterior  Surface  of  the  Heart.      (Bourgeey.) 

1,  Right  ventricle.  2,  Left  ventricle.  4,  Right  auricle.  5,  Left  auricle. 
6,  Pulmonary  artery.  7,  Aorta.  8,  Vena  cava  superior.  9,  Anterior  coro- 
nary artery.      10,  Posterior  coronary  artery.      11,  Coronary  vein. 

by  means  of  isolated  columns  of  muscle  called  the  pectinate  muscles. 
These  pectinate  muscles  make  the  interior  of  the  heart  present  an 
uneven,  ridgelike  appearance.  On  the  partition  between  the  auricles 
there  is  a  shallow,  oval  fossa,  with  a  border,  which  is  the  position  of  the 
foramen  ovale,  by  which  the  two  auricles  communicated  during  intra- 


THE  CIRCULATION. 


205 


uterine  life.     The  openings  of  small  veins,  the  foramina  Thebesii,  can 
be  seen  at  various  parts  of  the  inner  surface  of  the  right  auricle. 

The  auriculo-ventricular  orifice  of  the  right  side  of  the  heart  is 
a  large  oval  aperture.  It  is  about  an  inch  in  diameter.  It  is  guarded 
by  the  tricuspid  valve,  or  right  auriculo-ventricular  ralve. 


Fig.  63. — Heart  of  the  Cow,  with  Left  Auricle  and  Ventricle  Laid 
Open.      ( MuLLER. ) 

a,  Root  of  the  aorta.  6,  Spaces  in  the  wall  of  the  auricle.  r,  c.  Orifices 
of  the  pulmonary  veins.  1,  1,  Pulmonary  veins.  p,  p.  Papillary  muscles. 
q,  q,  Columnae  carneae.  A,  Orifice  of  the  aorta.  K,  Left  ventricle.  S,  Septum. 
r,  Left  auricle.  W,  Lateral  wall  of  left  ventricle.  1,  1,  2,  Leaflets  of  mitral 
valve. 


The  left  auricle  has  thick  walls,  and  the  walls  are  not  so  trans- 
lucent as  those  of  the  right  auricle.  It  has  a  smooth  interior  surface, 
except  with  the  auricular  appendage,  where  pectinate  muscles  are 
present.  It  has  four  openings,  which  are  the  pulmonary  veins,  two 
in  the  right  and  two  in  the  left  side  of  the  auricle.     At  the  lower 


206 


PHYSIOLOGY. 


anterior  part  of  the  cavity  is  the  left  aurieulo-ventricular  orifice.  The 
right  ventricle  is  in  the  shape  of  a  pyramid  with  the  base  upward  and 
backward.  It  extends  from  the  right  auricle  to  near  the  apex  of  the 
heart,  and  occupies  more  of  the  front  surface  of  the  heart  than  the 
left  ventricle.  The  walls  of  the  right  ventricle  are  only  one-third 
the  thickness  of  those  of  the  left.  The  septum  ventriculorum  bulges 
into  the  right  ventricle.  There  are  numerous  projecting  ridges  in  the 
right  ventricle  which  are  muscles  called  the  columnaB  carneae.     Some 


Fig.  64. — Diagram  of  Mammalian  Heart.      (Beclard.) 

a.  Left  ventricle.  b.  Right  ventricle.  c,  Left  auricle.  d,  Right  auricle. 
f,  Aorta.  {/,  {I,  Pulmonary  arteries.  h.  Inferior  vena  cava.  i,  Superior  vena 
cava.  k.  Orifice  of  superior  vena  cava.  /,  Orifice  of  inferior  vena  cava. 
m,  Orifice  of  the  coronary  vein.  o,  Left  pulmonary  vein.  p.  Right  pulmonary 
vein.  r.  Orifice  of  the  right  pulmonary  vein.  s.  Orifice  of  the  left  pulmonary 
vein. 


of  them  are  named,  from  their  shape,  the  papillary  muscles,  which 
project  from  the  interior  surface  of  the  ventricle  and  end  in  narrow 
tendinous  cords   called  the  chordae  tendineae. 

The  right  aurieulo-ventricular  orifice  opens  into  the  ventricle  at 
its  lower  back  part.  From  its  edges  projects  a  broad,  membranous 
fold  divided  into  three  parts  and  hence  called  the  tricuspid,  whose 
free  borders  are  attached  by  the  chordae  tendineae  to  the  papillary 
muscles  and  to  other  points  on  the  interior  surface  of  the  ventricle. 


THE  CIRCULATION. 


207 


When  the  valve  is  open  the  three  parts  lie  against  the  interior  surface 
of  the  ventricle.  The  duplicature  of  the  endocardium  with  included 
fibrous  tissue  makes  up  the  tricuspid  valve  and  the  chordae  tendineae. 
The  pulmonary  artery  springs  from  the  base  of  the  right  ventricle. 
Its  opening  is  provided  with  three  semilunar  valves.  These  valves  are 
three  crescentric  doublings  of  the  endocardium  with  fibrous  tissue  and 
are  arranged  in  a  circle.  Their  convex  border  is  attached  around 
the  edge  of  the  orifice  of  the  artery.  Behind  each  valve  the  artery 
is  dilated  into  a  shallow  pouch,  called  the  sinus  of  Valsalva,  which 

Pulmonary  valve. 


Aortic 
valve. 


Bicuspid 
valve.    ■ 


Fig.  65. — Valves  of  Heart. 

prevents  the  valve.  Avhen  open,  from  adhering  to  the  side  of  the  artery 
and  permits  the  reflow  of  blood  readily  to  press  the  valve  down  to 
close  the  opening.  At  the  middle  of  the  free  border  of  the  valve  there 
is  a  thickening  of  fibrous  tissue,  making  the  corpora  Arantii.  The 
left  ventricle  is  three  times  the  thickness  of  the  right,  and  its  apex 
forms  the  apex  of  the  heart.  It  is  longer  and  forms  more  of  the 
posterior  surface  of  the  heart  than  the  right  ventricle.  Like  the 
right  ventricle,  it  has  columnjE  carneae,  papillary  muscles,  and  chords 
tendines. 

The  left  auriculo-ventricular  valve  is  provided  with  a  pair  of 
membranous  folds  forming  the  mitral  valve,  or  bicuspid  valve.  It 
is  larger  in  size  and  thicker  than  the  right  auriculo-ventricular  valve. 
These  mitral  segments  have  the  chordae  tendineae  attached. 


208  PHYSIOLOGY. 

The  left  ventricle  has  an  opening  which  is  the  origin  of  the  great 
blood-vessel,  the  aorta.  It  is  provided  with  semi-lunar  or  sigmoid 
valves,  of  the  same  character  as  those  of  the  pulmonary  artery. 

Structure  of  the  Heart. 

The  lining  membrane  of  the  heart  is  called  the  endocardium. 
All  the  valves  of  the  heart  are  made  up  by  its  inclosing  fibrous  tissue. 
The  endocardium  is  formed  of  epithelium  and  fibro-elastic  tissue. 
The  rings  to  which  the  valves  are  attached  are  also  made  of  endo- 
cardium and  fibro-elastic  tissue. 

Muscular  Structure  of  the  Heart. 

The  muscular  fibers  of  the  auricles  consist  of  two  layers  running 
in  different  directions.  The  external  fibers  are  common  to  both 
auricles,  while  some  run  into  the  interauricular  septum.  The  internal 
fibers  are  not  common  to  both  auricles,  but  are  confined  to  each 
auricle.  The  fibers  of  the  internal  layer  are  attached  to  their  respec- 
tive auriculo-ventricular  rings.  The  external  fibers  run  in  a  trans- 
verse direction;  the  internal  fibers  cross  the  direction  of  the  former. 
There  are  other  muscular  fibers,  arranged  concentrically  around  the 
origin  of  the  great  veins  and  auricular  appendages. 

In  the  ventricles  there  are  several  layers  of  muscles.  The  outer 
layer  runs  from  the  base,  where  they  are  attached  to  the  fibro-car- 
tilaginous  rings  around  the  orifices,  toward  the  apex  of  the  heart, 
where  they  run  by  a  sharp  twist  into  the  interior  of  the  left  ventricle 
to  the  papillary  muscles.  This  twisting  of  the  fibers  gives  rise  to  the 
whorl  of  the  fibers  at  the  apex  of  the  heart.  Other  fibers  run  obliquely 
upward  in  the  septum  to  be  attached  to  the  fibro-cartilaginous  ring, 
from  which  they  started.  Still  other  fibers  pass  in  a  horizontal  direc- 
tion into  the  posterior  wall  of  the  left  ventricle  and  take  a  ringlike 
course  in  it. 

The  right  ventricle  in  the  arrangement  of  its  muscular  fibers  may 
be  regarded  as  an  appendage  of  the  left. 

Histology. — The  fibers  of  the  heart  are  striated.  Unlike  the 
voluntary  muscle,  they  branch  and  have  their  ends  united  to  each 
other  so  as  to  form  a  network.  The  open  space  in  the  network  is 
filled  with  connective  tissue  and  lymphatics.  The  muscle-cells  are 
quadrangular  in  shape,  with  clear  oval  nuclei.  There  is  no  sar- 
colemma  in  heart-muscle.  The  muscles  of  the  heart  anastomose  and 
divide.     As  to  lymphatics,  the  heart  is  very  liberally  supplied  with 


THE  CIRCULATION. 


209 

The  muscu- 


them.     The  nerves  are  nonmedullated  near  their  ends 
lar  mass  of  the  heart  is  called  the  myocardium. 

Pericardium. — This  is  a  fibro-serous  sac  inclosing  the  heart,  and 
consists  of  two  leaves,  or  layers.  The  internal  serous,  or  visceral, 
layer  closely  invests  the  heart  and  the  commencement  of  the  great 
blood-vessels.     It  is  an  inextensible  membrane. 


n 

Fig.  06. — Course  of  Muscular  Fibers  of  Heart.      (Landois.  ) 

I.  Course  of  the  muscular  fibers  on  the  left  auricle,  with  the  outer  trans- 
verse and  inner  longitudinal  fibers,  the  circular  fibers  on  the  pulmonary  veins 
(r.   p.).    T,  The  left  ventricle.    (John  Reid.) 

II.  Arrangement  of  the  striped  muscular  fibers  on  the  superior  vena  cava. 
a,  Opening  of  the  vena  .izygos.      Y,  Auricle.    (Elischer.) 

The  external  filirous.  or  parietal,  layer  is  a  strong,  inelastic  mem- 
brane which  embraces  the  origin  of  the  great  blood-vessels  at  the 
base  of  the  heart. 

These  two  layers  unite  to  make  a  close  sac.  Between  the  pari- 
etal and  visceral  layers  is  the  pericardial  liquor,  which  permits  the 
two  layers  to  slide  on  each  other  without  friction.     The  elastic  fibers 

14 


210 


PHYSIOLOGY. 


in  the  parietal  layer  permit  of  its  following  very  closely  the  chang- 
ing form  of  the  heart. 

The  Auricles. — In  examining  each  half  of  the  heart  it  is  easy  to 
recognize  that  the  auricle,  on  account  of  the  thinness  and  the  weak- 
ness of  its  muscular  walls,  can  scarcely  be  the  important  part  of  that 
organ.  In  laying  bare  the  heart  of  an  animal  while  artificial  respira- 
tion is  maintained,  it  is  seen  that  the  action  of  the  auricle  is  very  weak 
as  compared  with  that  of  the  ventricle.  A  manometer  introduced 
into  the  auricular  cavity  at  the  moment  when  it  contracts  marks  a 


Fig.  67. — Course  of  the  Ventricular  Muscular   Fibers.      (LandOIS.) 

A,  On  the  anterior  surface.  B,  View  of  the  apex  with  the  vortex.  V, 
Course  of  the  fibers  within  the  ventricular  wall.  D,  Fibers  passing  into  a 
papillary  muscle,   P. 


pressure  that  is  five  or  six  times  less  than  that  obtained  in  the  corres- 
ponding ventricular  cavity  under  the  same  conditions. 

The  pressure  in  the  auricles  is  lowest  at  the  period  of  diastole, 
and  since,  then,  the  pressure  in  the  veins  is  greater  than  the  pres- 
sure in  the  auricles,  there  is  a  flow  of  blood  into  the  auricles,  which 
gradually  becomes  less.  When  the  ventricles  dilate,  another  fall  in 
the  auricular  pressure  takes  place  and  another  rush  of  venous  blood 
follows.     The  opening  of  the  great  veins  is  contracted,  and  this  act, 


THE  CIRCULATION.  211 

preceding  the  contraction  of  the  auricle,  drives  the  blood  from  the 
veins  into  the  auricles.  When  the  auricles  contract,  the  blood  can- 
not flow  back  into  the  veins  to  any  great  extent. 

The  Ventricles. — The  ventricles  represent  the  parts  that  are 
really  active  in  the  cardiac  circulation.  The  strength  of  the  contrac- 
tions proper  to  the  two  ventricles  reveals  itself  in  the  thickness  of  the 
muscular  walls,  the  fibers  of  which  are  inserted  into  fibrous  rings. 
These  latter  are  the  veritable  skeleton  of  the  heart.  Manometric 
observation  presents  us  with  proof  of  the  force  of  the  ventricular 
contractions. 

GENERAL  COURSE   OF  THE  CIRCULATION. 

Since  the  main  points  of  the  anatomy  of  the  heart  have  been 
touched  upon,  it  might  be  well  at  this  stage  roughly  to  consider  the 
circuit  of  the  blood  through  it  and  its  vessels.  The  vascular  system 
is  a  closed  apparatus  consisting  of  a  central  pump  with  its  vessels 
leading  to  every  part  and  organ  of  the  economy.  All  vessels  lead- 
ing aivay  from  the  heart  are  arteries;  those  leading  toward  it  are 
veins. 

The  entire  circuit  of  the  blood  is  divided  into  two  principal  por- 
tions, which  are  distinctly  separated  from  one  another  both  ana- 
tomically and  functionally.  The  one  conveys  the  blood  to  and  from 
the  lungs  during  the  process  of  aeration;  so  that  to  it  has  been 
affixed  the  term  pulmonary  circulation.  The  other  has  for  its  func- 
tion the  distribution  of  the  blood  to  all  parts  and  organs  of  the 
economy  in  general,  thereby  receiving  the  name  systemic  circulation. 

Beginning  with  the  left  ventricle,  the  blood  is  conveyed  to  the 
aorta,  from  which  branches  are  distributed  to  every  part  of  the  body, 
through  the  capillaries  to  the  veins,  to  be  eventually  returned  as 
dark,  impure  blood  to  the  right  auricle.  This,  the  greater  circuit, 
has  been  termed  the  systemic  circulation.  During  the  course  of  this 
circulation  it  has  been  found  that  the  blood  from  the  capillaries  of 
some  of  the  abdominal  viscera  is  gathered  together  into  a  single  ves- 
sel, the  portal  vein,  which  again  subdivides  to  form  a  capillary  plexus 
in  the  liver.  This  accessory  circulation  is  commonly  designated  as 
the  portal  circulation. 

From  the  right  auricle  the  blood  flows  into  the  right  ventricle, 
from  which  it  is  expelled  through  the  pulmonary  artery  to  the  lungs, 
to  be  returned  to  the  left  auricle  as  bright-red,  pure  blood.  This 
change  in  color  is  due  to  the  presence  of  oxygen  in  the  haemoglobin 


212 


PHYSIOLOGY. 


gained  during  the  process  of  aeration.     This  shorter  circuit  is  known 
as  the  lesser,  or  pulmonary,  circulation. 

Difference  of  pressure  between  the  blood  of  the  aorta  and  pul- 
monary artery,  on  the  one  hand,  and  that  in  the  venue  cavae  and  pul- 
monary veins,  on  the  other  hand,  is  responsible  for  the  flow  of  blood. 


Fig.    6S. — Diagram  of  the   Circulation.      (Duval.) 

1,  Left  ventricle.  2,  Left  auricle.  3,  Right  ventricle.  4,  Right  auricle. 
5,  Aorta.  6,  Systemic  capillaries.  7,  Inferior  vena  cava.  S,  Pulmonary 
artery.  9,  Pulmonary  capillaries.  10,  Pulmonary  vein.  11,  Gastric  and  intes- 
tinal vessels.  12,  Intestine.  13,  Portal  vein.  14,  Portal  vein,  forming  second 
capillary  system  in  the  liver  15,  Liver.  16,  Hepatic  vein.  17,  Pulmonary,  or 
lesser,    circulation.     18,  Systemic,   or   greater,    circulation. 

Its  direction  is  always  in  the  line  of  least  resistance.  The  greater 
the  difference  of  pressure,  the  greater  is  the  velocity  of  the  blood- 
stream; the  reduction  of  this  difference  to  nil,  as  in  death,  results 
in  no  movement.   ' 


THE  CIRCULATION. 


213 


CHANGES  IN  THE  SHAPE  OF  THE  HEART. 

When  the  auricles  contract,  they  become  smaller.  When  the 
ventricles  contract,  the  base  of  the  heart  approaches  the  apex  (lur- 
ing the  contraction  of  the  fibers  running  in  a  longitudinal  direction. 
As  the  blood  escapes  from  the  ventricles,  then  the  lateral  and  antero- 
posterior diameters  lessen. 

CHANGE  IN  POSITION  OF  THE  HEART. 

In  diastole,  the  heart  hangs  downward  and  to  tlie  left  from  the 
line  of  its  basal  attachment.  During  contraction,  it  assumes  a  posi- 
tion at  right  angles  to  its  base  and  presses  the  heart  in  contact  with 
the  chest  more  vigorously,  producing  the  impulse  of  the  heart. 


01       02       03      04       05       06       07      08       09       lOeecs. 

I  [Heart  Sounds 
dup                                                Lnbb dup 

Fig.  69. — A  Cardiac  Cycle.     (Starling.) 

CARDIAC  REVOLUTION. 

The  cardiac  revolution  may  be  divided  as  follows:  (1)  the  first 
sound;  (2)  the  first,  or  short,  silence;  (3)  the  second  sound;  and, 
(4)  the  second,  or  long,  silence. 

If  the  cardiac  revolution  be  divided  into  tenths,  then  the  first 
sound  will  be  Yio ;  the  first  silence,  ^/^^o;  the  second  sound, -/if,;  and 
the  long  silence,  ^/^q. 

The  time  of  the  various  acts  of  the  total  cardiac  movement  in 
man  are,  according  to  Gibson,  as  follows: — 

Auricular  systole 0.112  second. 

Ventricular  systole   0.368  second. 

Ventricular  diastole   0.578  second. 

Cardiac  cycle    1.058  seconds. 


214 


PHYSIOLOGY. 


The  rhythmica,!  succession  of  these  acts  constitutes  the  cardiac 
revolution.  By  their  function  the  vital  fluid — the  blood — is  kept  in 
constant  circulation  within  the  body  so  that  every  portion  of  the 
economy  receives  its  proper  nourishment.  The  processes  of  meta- 
bolism are  balanced,  the  various  organs  and  glands  of  the  body  per- 
form their  needed  functions,  and  the  whole  animal  lives  and  thrives. 

The  events  in  a  cardiac  revolution  can  be  tabulated  as  follows : — 


1st   period. 

Auricular  Systole. 
Accomplishment  of  ven- 
tricular diastole. 


3d  period. 

General  diastole  of  the 
heart. 

Closure  of  semilunar 
valves. 

The  blood  pours  into 
the  auricles,  and  a 
little  into  the  ventri- 
cles. 


2d    period. 

Ventricular  systole. 

Closure  of  mitral  and 
tricuspid  valves. 

Opening  of  semilunar 
valves. 

The  blood  is  thrown  in- 
to the  aortic  and  pul- 
monary arteries. 

Cardiac  impulse. 

Diastole  of  the  arteries 
and  the  pulse. 

Auricular  diastole. 

To  physiologists,  the  first  period  in  the  movement  of  the  heart 
coincides  with  contraction  of  the  auricles.  The  clinicians  take  the 
first  period  at  the  moment  of  ventricular  systole. 

MOVEMENTS  OF  THE  HEART. 

The  heart  movements  consist  of  alternate  contractions  and 
relaxations,  which  follow  each  other  with  a  certain  rhythm.  Systole 
is  the  name  for  contraction;   diastole  is  the  term  for  relaxation. 

The  two  auricles  contract  and  relax  synchronously,  and  these 
movements  are  followed  by  a  simultaneous  contraction  and  relaxa- 
tion of  the  ventricles.  There  is  a  systole  and  diastole  of  auricles 
and  a  systole  and  diastole  of  ventricles.  At  last  there  is  a  very  short 
period  in  which  the  heart  is  in  diastole.  The  succession  of  move- 
ments from  the  commencement  of  one  auricular  systole  to  the  com- 
mencement of  one  immediately  following  is  known  as  a  cardiac  rev- 
olution. The  auricular  contraction  is  less  sudden  than  the  ventri- 
cular. The  contraction  of  the  auricle  lasts  a  very  short  time,  while 
the  time  of  ventricular  contraction  is  considerable,  and  the  relaxa- 
tion of  the  ventricle  is  slow. 

The  time  of  contraction  of  the  auricle  and  its  repletion  are  about 
the  same,  but  the  ventricular  diastole  is  nearly  twice  as  long  as  the 
ventricular  systole.     The  auricles  have  a  uniform,  wavelike  move- 


THE  CIRCULATION.  215 

ment;  the  ventricles  have  a  spasmodic  action  in  their  movement.  If 
now  the  venae  cava?  and  pulmonary  veins  are  delivering  blood  into 
the  two  auricles,  then  at  this  time  the  diastole  of  the  auricles  is 
gradually  approaching  completeness.  The  swelling  of  the  auricles  is 
due,  in  part,  to  the  pressure  in  the  veins  being  greater  than  in  the 
cavity  of  the  auricles  and  in  part  to  the  inspiratory  movement  of 
the  thorax  sucking  the  blood  from  the  veins  external  to  the  thorax 
to  the  interior  of  the  veins  of  the  chest.  During  this  period  the 
ventricles  are  filling  with  blood,  for  both  the  triscuspid  and  mitral 
valves  are  open.  As  the  cavity  of  the  auricles  is  smaller  tlian  that 
of  the  ventricles,  the  auricles  are  filled  sooner,  and  consequently  con- 
tract before  the  ventricles,  the  veins  offering  a  resistance  to  the 
backward  movement  of  the  blood  by  a  narrowing  of  their  opening. 
The  systole  of  the  auricle  forces  the  blood  chiefiy  in  the  line  of  least 
resistance  into  the  ventricle,  which  is  not  yet  completely  filled  and 
is  undergoing  diastole.  While  the  blood  is  passing  from  the  auricles 
into  the  ventricles  the  auriculo-ventricular  valves  are  floated  grad- 
ually into  a  horizontal  position.  The  blood  by  the  systole  of  the 
auricles  has  filled  the  ventricles,  already  filled  in  part  during  the 
diastole  of  the  auricle.  Now  the  ventricles  contract,  the  mitral  and 
tricuspid  valves  are  tightly  pressed  together,  and  regurgitation  of 
blood  into  the  auricles  is  prevented.  Now,  as  the  blood  cannot  go 
back  into  the  auricles,  it  must  by  the  muscular  force  of  the  ven- 
tricles rush  into  the  pulmonary  artery  and  aorta,  respectively.  The 
onset  of  the  blood  forces  open  the  semilunar  valves  of  the  pulmonary 
artery  and  aorta,  and  exerts  a  pressure  in  these  arteries  partially 
filled  with  blood  before  the  new  rush  of  blood  sets  in.  Their  walls 
are  necessarily  considerably  distended.  Then  the  ventricles  dilate 
and  at  the  same  time  the  mitral  and  tricuspid  valves  open,  and  the 
semilunar  valves  close  from  the  recoil  of  blood  against  them.  From 
the  time  the  systole  of  the  ventricles  ends  to  the  full  distension  of 
the  auricles,  all  the  chambers  of  the  heart  are  in  diastole  and  are 
being  filled  with  blood.  This  is  the  resting  of  the  heart,  and  is  called 
the  pause. 

Pathological  Cardiac  Action. — An  increase  in  the  heart's  action 
is  produced  by  any  resistance  either  to  the  heart  itself  or  to  any  of 
its  blood-vessels.  With  increased  action  the  heart-muscle  under- 
goes hypertrophy,  and  frequently,  dilatation  also. 

The  most  common  resistance  met  with  in  the  vessels  is  narrow- 
ing of  their  lumen  or  want  of  elasticity  in  their  walls.  Within  the 
heart  the  most  usual  defects  are  narrowing  of  the  orifices  or  incom- 


216 


PHYSIOLOGY. 


petency  of  the  valves.  On  account  of  the  latter  condition  blood  is 
allowed  to  escape  in  the  wrong  direction  so  that  the  heart  must  do 
extra  work  to  keep  all  of  it  in  circulation. 

Palpitation  and  syncope  are  two  very  common  conditions  met 
with,  and  they  are  due  to  faulty  heart-action,  induced  perhaps  by 
causes  that  are  more  or  less  remote. 

The  Cardiac  Impulse. — Synchronous  with  this  is  "apex-beat,'^  by 
which  is  understood  that  surface  movement  which  is  seen  or  the 
impulse  that  can  be  felt  within  a  circumscribed  area  and  is  produced 
by  ventricular  systole.  This  area  is  located  in  the  fifth  left  inter- 
costal space  between  the  mammary  and  midsteriial  lines.  The  cen- 
ter of  this  area  is  described  as  being  two  inches  below  the  nipple  and 
one  inch  to  its  sternal  side. 


Fig.  70. — SiiiuIi'iHon   Cardiograph. 

The  cause  of  the  impulse  of  the  heart  is  not  the  apex  but  the 
change  in  form  and  consistency  of  the  ventricles,  when  these  pass 
from  the  diastole  to  the  systole  and  in  the  instantaneous  transforma- 
tion.    It  is  the  sudden  hardening  of  the  ventricle. 

The  impulse  takes  place  at  the  same  time  as  the  systole  of  the 
ventricle,  and  is  caused  by  the  ventricle,  which  is  pressed  very  firmly 
against  the  chest.  At  the  time  of  the  contraction  of  tlie  ventricle 
the  outline  of  the  heart  changes;  instead  of  being  an  oblique  cone 
having  an  elliptical  base,  as  at  rest,  it  becomes  a  regular  cone  with 
a  regular  base. 

For  giving  more  accurate  accounts  of  the  heart's  movements 
recourse  is  had  to  the  instruments  called  cardiographs. 

Cardiographs. — These  are  instruments  which  give  graphic  rec- 
ords of  the  heart's  movements.  They  register  at  the  same  time  the 
movements  of  the  auricles,  ventricles,  and  the  beating  of  the  heart 


THE  CIRCULATION. 


217 


against  the  walls  of  the  chest.  For  obtaining  these  records  of  ani- 
mals the  heart  was  exposed,  and  levers  were  attached  to  various  parts 
of  it  so  that  their  distal  ends  could  make  tracings  upon  a  revolving, 
blackened  surface. 

This  apparatus  was  inapplicable  for  use  upon  the  human  heart, 
but  there  are  to-day  for  its  study  numerous  cardiographs,  all  of 
them,  however,  being  only  modifications  of  Marey's  tambours. 

Sanderson^s  instrument  consists  of  a  hollow  disc,  the  rim  and 
back  of  which  are  of  brass,  while  the  front  is  of  thin  rubber.  On 
its  back  is  a  flat  steel  spring  bent  at  right  angles,  and  its  unattached 
end  is  provided  with  an  ivory  button  which  is  directly  over  the  cen- 
ter of  the  rubber  membrane.  The  ivory  button  is  applied  over  the 
point  where  the  apex-beat  is  most  plainly  felt.     During  the  applica- 


Fig.  71. — Cardiogram   (B)  witli  Simultaneous  Record  of  Heart- 
sounds  (A).     ( HuRTHLE,  Starling. ) 

1,  Position  of  first  sound.  2,  Position  of  second  heart-sound.  The  first 
heart-sound,  corresponding  to  the  systole  of  the  ventricle,  begins  at  the  notch 
in  the  cardiogram  near  the  top  of  the  ascent;  hence  the  ascent  of  curve  pre- 
ceding this  notch  is  due  to  auricular  systole  forcing  blood  into  the  ventricle, 
and   the   ventricular  systole   is   indicated   by  the   notch. 

tion  of  the  apparatus  the  ivory  button  is  kept  continually  in  motion 
by  the  surface  pulsations.  Each  movement  of  the  button  sets  the 
rubber  membrane  in  motion,  and,  as  the  drum  is  airtight  and  in 
communication  with  a  second  drum  with  a  recording  lever,  the 
diminution  of  air  in  the  first  causes  an  increase  in  the  content  of  air 
in  the  second,  and  an  elevation  of  its  recording  lever  on  a  smoked 
drum.  Each  systole  of  the  ventricle  causes  a  sudden  rise  of  the 
lever,  and  the  end  of  the  systole  is  noted  by  a  marked  gradual  descent 
of  it. 

The  cardiogram  is  read  from  right  to  left,  and  normally  shows  a 
small  elevation,  corresponding  to  auricular  systole,  immediatelv  suc- 
ceeded by  a  very  abrupt  rise  which  marks  ventricular  svstole.     This 


218  PHYSIOLOGY. 

is  held  for  0.3  of  a  second  and  presents  small  vibrations,  which  are  at- 
tributed to  the  closure  of  the  semilunar  valves.  The  very  abrupt, 
downward  stroke  marks  the  pause,  or  diastole. 

Clinically^  changes  in  the  cardiac  impulse  are  best  ascertained 
by  using  any  of  the  graphic  instruments  and  then  studying  the  curves 
obtained.  From  such  study  the  observer  is  able  to  get  very  definite 
knowledge  as  to  the  nature  of  the  cardiac  lesion,  its  severity,  etc.  The 
various  stenoses,  insufficiencies,  hypertrophies,  and  dilatations  may  by 
this  means  be  diagnosed  with  considerable  accuracy. 

Endocardiac  Pressure. — The  ordinary  mercurial  manometer,  by 
which  the  heart's  work  can  be  estimated,  is  unsuitable  for  determin- 
ing its  ventricular  pressure.  The  objections  are  the  relatively  great 
amount  of  work  required  to  produce  a  given  displacement  of  the  mer- 
cury; that  it  is  not  susceptible  and  sensitive  to  quickly  follow  differ- 
ences of  pressure;  and  when  once  displaced,  the  mercury  possesses 
enough  oscillations  of  its  own  which  confuse  oscillations  of  blood- 
pressure.  However,  when  this  instrument  by  the  introduction  of  a 
properly  placed  valve  is  converted  into  a  "maximum  and  minimum 
manometer,"  the  actual  blood-pressure  may  be  more  readily  deter- 
mined. 

The  dog  has  been  very  extensively  used  for  the  application  of  this 
instrument,  as  a  consequence  of  which  the  appended  figures  are 
given : — 

Systole.  Diastole. 

Maximum  Pressure.  Minimum  Pressure. 

Left  ventricle    140  millimeters — 30  to  40  millimeters. 

Right  ventricle 60  "  —  15  " 

Right   auricle    20  "  —  7  to     8 

By  negative  pressure  is  meant  that  the  mercury  in  the  instru- 
ment has  been  sucked  toward  the  heart.  The  negative  pressure,  as 
is  seen,  occurs  only  during  the  diastole  of  the  heart.  Moens  is  of  the 
opinion  that  this  negative  pressure  within  the  ventricle  happens 
shortly  before  the  systole  has  reached  its  height.  During  negative 
pressure  the  blood  from  the  veins  is  sucked  into  the  heart. 

For  determination  of  the  duration  of  the  cardiac  events,  as  well 
as  the  blood-pressure — that  is,  to  have  tracings  of  the  curves  for  each 
cavity,  to  know  the  time-relations  for  comparisons,  as  well  as  the 
curves  of  the  great  arteries  and  veins — requires  an  instrument  of 
some  complexity.  Only  within  recent  years  have  these  been  invented, 
by  Chauveau  and  Marey,  whereby  elastic  manometers  counterbalance 
the  blood-pressure  instead  of  a  column  of  liquid.     Many  of  the  in- 


THE  CIRCULATION.  219 

struments  employed  give  their  tracings  from  movements  transmitted 
to  them  from  cardiac  sounds  through  a  tube  to  the  recording  appa- 
ratus. The  sounds  were  usually  appropriately  curved  cannula?,  to 
one  end  of  which  were  attached  flexible  rubber  bags,  or  ampullae. 
Two  were  introduced  through  the  jugular  vein  into  the  right  auricule 
and  ventricle,  a  third  into  an  intercostal  space  in  front  of  the  heart. 
These  were  put  into  communication  with  three  tambours  with  their 
needles,  by  which  were  recorded  the  endocardiac  pressure  with  the 
duration  of  the  auricular  and  ventricular  contractions. 

By  these  levers  it  was  shown  without  doubt  that  the  apex-beat 
is  due  to  the  systole  of  the  ventricle,  as  the  two  were  synchronous. 


'  z 

.3  4 

r' 

' . y^-' 

~~ — -. — , 

~^j 

~-  — ,J 

1  z 

3  4 

Line  of  a'mosplieric 
pressure. 


Fig.  72. — Magnified  curve  of  the  course  of  pressure  within  the  left 
ventricle  and  the  aorta  of  the  dog,  the  chest  being  open;  to  be  read 
from  left  to  right.  Recorded  simultaneously  by  two  elastic  manometers 
with  transmission  by  liquid.      (Porter.) 

In  both  curves  the  ordinates  having  the  same  numbers  have  the  foHowing 
meaning:  1,  The  instant  preceding  the  closing  of  the  mitral  valve.  2,  The 
opening  of  the  semilunar  valve.  3,  The  beginning  of  the  "dicrotic  wave," 
regarded  as  marking  the  instant  of  closure  of  the  semilunar  valve.  4,  The 
instant  preceding  the  opening  of  the  mitral  valve. 

Pressure  Curve  in  the  Ventricle. — Experiments  on  ventricular 
pressure  have  been  made  with  Fick's  elastic  manometer  and  the  dif- 
ferential manometer  of  Hiirthle.  Dr.  Porter,  of  Harvard,  has  made 
a  study  of  this  subject  with  the  instrument  of  Hiirthle,  and  I  shall 
follow  him  in  the  description  of  the  curves  obtained. 

Porter  (Fig.  72),  with  his  predecessors,  has  shown  that  the 
systolic  muscular  contractions  begin  quite  suddenly,  producing  a  swift 
rise  of  pressure.  The  diastolic  fall  of  pressure  is  nearly  as  sudden 
as  the  rise.  In  the  fall  of  diastolic  pressure,  the  pen  often  reaches 
below  the  pressure  of  the  atmosphere.  Between  the  systolic  rise  and 
the  diastolic   fall   it   is   found  that  the   systolic  pressure   causes  its 


220  PHYSIOLOGY. 

curve  to  bend  alternately  downward  and  upward.  Between  these 
two  points  the  general  direction  of  the  curve  approaches  the  hori- 
zontal, and  thus  may  be  denominated  the  "systolic  plateau."  The 
curve  of  intraventricular  pressure  rarely  gives  any  clear  indication 
of  the  beginning  or  end  of  auricular  systole.  The  ventricular  pres- 
sure curve  does  not  give  any  clear  indication  of  the  moment  of  clos- 
ing or  opening  of  either  auriculo-ventricular  or  semilunar  valves. 
These  instances  can,  however,  be  marked  upon  it  after  they  have  been 
obtained  in  an  indirect  manner. 

In  Fig.  72  the  ordinate  1  indicates  the  closing,  and  ordinate  4 
the  opening  of  the  mitral  valve;  ordinate  2  indicates  the  opening, 
and  ordinate  3  the  closing  of  the  aortic  valve.  In  the  arterial  curve, 
2  marks  the  beginning  of  the  systolic  rise  and  3  the  beginning  of 
the  dicrotic  wave,  which  corresponds  closely  to  the  closure  of  the 
aortic  valve. 

During  the  period  when  the  bicuspid  valve  is  open,  the  pres- 
sure is  lower  in  the  ventricle  than  in  the  artery,  the  aortic  valve  is 
shut,  and  blood  is  entering  the  ventricle,  this  being  the  "period  of 
the  reception  of  blood,"  During  the  greater  part  of  the  period 
when  the  bicuspid  valve  is  shut,  the  aortic  valve  is  open,  the  pressure 
is  higher  in  the  ventricle  than  in  the  artery,  the  ejection  of  blood 
is  taking  place,  this  being  the  "period  of  ejection,"  which  lies  between 
the  ordinates  2  and  3  (Fig,  72). 

There  are  two  brief  periods,  during  each  of  which  both  valves 
are  shut  and  the  ventricle  is  a  closed  cavity;  one  immediately  pre- 
cedes the  period  of  ejection,  the  other  immediately  follows  it.  The 
explanation  of  these  periods  is  that  it  takes  a  brief  time  for  the 
cardiac  muscle,  contracting  upon  the  blood  in  the  closed  ventricle, 
to  raise  the  pressure  to  the  high  point  required  to  overcome  the 
opposing  pressure  within  the  artery  and  to  open  the  aortic  valve. 
Hence  the  ventricular  cycle  is  composed  of  four  periods:  the  first, 
the  period  of  complete  closure  with  strongly  rising  pressure;  the 
second,  the  period  of  ejection,  relatively  long;  the  third,  a  period  of 
complete  closure,  with  swiftly  falling  pressure;  the  fourth  is  the 
period  when  the  pressure  is  low  and  blood  is  entering  the  ventricle. 

Persistence  of  the  Heart  Movement. — The  heart  may  continue 
to  beat  for  some  time  after  its  removal  from  the  body.  This  is  par- 
ticularly noticeable  in  cold-blooded  animals  like  the  turtle,  whose 
heart  movements  have  been  known  to  continue  even  for  days. 

When  the  heart  dies  the  ventricles  stop  first,  but  the  right  auricle 
is  the  last  to  be  arrested;  hence  it  is  called  the  "  ultimum  moriens." 


THE  CIRCULATION.  221 

50UNDS  OF  THE  HEART. 

When  the  ear  is  placed  over  the  cardiac  region,  or  to  a  stetho- 
scope applied  to  the  precordial  area,  two  characteristic  sounds  are 
heard.  The  two  sounds  are  known  as  the  first  sound  and  second 
sound,  and  are  emitted  during  every  cardiac  revolution.  Though  the 
sounds  occur  in  quick  succession,  yet  they  are  each  separated  by 
silences. 

The  first  sound  is  the  stronger  of  the  two.  In  nature  it  is  dull. 
It  coincides  with  the  shock  of  the  heart.  The  first  sound  is  fol- 
lowed by  the  first,  or  short,  silence. 

The  second  sound  is  shorter  in  duration  and  clearer  in  character 
than  the  first.  It  conies  an  instant  afterward,  at  the  moment  when 
the  whole  heart  is  in  relaxation.  In  pitch,  the  second  sound  is  from 
one-fourth  to  one-third  higher  than  that  of  the  first  sound. 

Following  the  second  sound  of  the  heart  there  occurs  the  second, 
or  long,  silence.  In  reality  the  pause  occupies  but  a  fraction  of  a 
second,  yet  it  is  said  to  be  "long"  as  compared  with  the  first  silence. 

It  must  be  borne  in  mind  by  the  student  that  there  occur  in 
reality  four  sounds  during  each  cardiac  cycle.  However,  the  first 
two  normally  occur  in  unison,  as  do  the  second  two,  so  that  but  two 
sounds  are  heard  by  the  examiner. 

From  their  difference  in  pitch  the  two  heart-sounds  may  be 
expressed  graphically  upon  the  musical  staff.  To  the  ear  they  sim- 
ulate the  sounds  which  are  produced  in  pronouncing  the  words, 
"lubb,"  "dup,"  the  former  corresponding  to  the  first  heart-sound, 
the  latter  to  the  second. 

If  the  two  sounds  be  listened  to  at  some  distance  from  the  heart, 
the  first  may  nearly  always  be  distinguished  from  the  second  by  com- 
paring the  intervals  between  them.  The  time  elapsing  between  the 
first  and  second  sounds  is  generally  much  shorter  than  that  which 
separates  the  second  sound  from  the  first  in  the  succeeding  revolu- 
tion of  the  heart.  But,  in  medical  practice,  too  much  importance 
must  not  be  attached  to  these  intervals,  since  their  respective  dura- 
tion is  extremely  variable.  In  the  absence  of  the  impulse  it  is  bet- 
ter to  depend  upon  the  differences  of  pitch. 

Causes  of  the  Sounds. — The  nature  and  causes  of  the  cardiac 
sounds  are  best  studied  in  a  large  mammal  whose  heart-action  is 
comparatively  slow.  For  this  purpose  the  horse  is  used.  Its  pulse 
averages  but  forty.  The  animal  is  properly  prepared  by  anaesthe- 
tizing, curarizing,  and  exposing  the  viscus  to  view  by  placing  a  win- 


222  PHYSIOLOGY. 

(low  in  the  thorax.  With  stethoscope  and  by  observation  and  pal- 
pation, the  experimenter  is  ready  to  determine,  among  the  complex 
actions  which  make  up  a  cardiac  cycle,  the  one  which  gives  rise  to 
each  of  the  two  sounds. 

Second  Sound. — The  cause  of  the  second  sound  is  the  sudden 
closure  of  the  sigmoid  (semilunar)  valves  of  the  aorta  and  pulmonary 
artery  during  relaxation  of  the  ventricle.  The  sudden  closing  of 
the  valves  is  produced  during  the  effort  of  the  arterial  blood  to 
escape  backward  from  the  elastic  reaction  of  the  aorta  and  pulmon- 
ary artery. 

Proofs  abound  in  support  of  this  theory.  If  the  valvular  move- 
ments be  hindered  in  one  of  the  above-mentioned  arteries  by  placing 
a  clamp  close  to  its  base,  immediately  the  second  sound  is  suppressed 


Fig.  73. — The  Action  of  the  Semilunar  Valves.     (Chauveau.) 

Pp,  Tracing  of  the  variations  of  pressure  in  the  left  ventricle.  2,  Means 
second  sound.  8,  Tracing  by  the  signal  magnet,  showing  the  action  of  the 
valve  which  by  its  movements  closes  and  opens  an  electric  current  to  the  signal 
magnet.  The  second  sound  (closure  of  the  semilunar  valves)  corresponds  to  the 
moment  when  the  ventricle  relaxes,  that  is,  at  the  beginning  of  the  ven- 
tricular diastole. 

at  that  point.  If  the  valvular  action  of  both  vessels  be  suppressed, 
the  second  sound  may  be  completely  extinguished. 

Again,  should  the  apex  of  the  heart  be  cut  off  and  the  ventri- 
cular blood  be  made  to  escape  to  the  outside,  no  second  sound  occurs. 
In  this  experiment  the  sigmoid  valves  have  neither  been  lifted  up 
nor  allowed  to  fall  back  and  stretch  themselves  out  with  a  sound. 

Physically,  one  is  able  to  account  for  the  production  of  the 
second  sound  on  the  principle  that  it  is  produced  by  the  clicking  of 
the  sigmoid  valves.  In  fact,  similar  sounds  are  obtained  by  produc- 
ing sudden  tension  of  a  membrane  under  the  action  of  a  column  of 
liquid. 

When  the  initial  stump  of  an  aorta,  whose  valves  are  still  intact, 
is  attached  to  a  tube  and  the  reflux  of  the  liquid  closes  the  valves,  a 
clear,  snappy  click  is  produced. 


THE  CIRCULATION.  223 

When  pathological  conditions  occur,  the  sound  is  altered,  being 
accompanied  by  or  even  altogether  replaced  by  a  blowing  sound, 
known  as  a  "munnur." 

The  Cause  of  the  Fisst  Sound  is  more  difficult  to  determine 
than  is  that  of  the  second.  The  nature  of  this  sound  is  more  com- 
plex, several  factors  entering  into  its  evolvement. 

Since  it  is  established  that  the  first  sound  corresponds  in  point 
of  time  with  ventricular  systole,  it  is  reasonable  to  connect  it  with 
one  or  several  phenomena  which  take  place  in  the  heart  at  that 
moment.  They  are:  The  precordial  shock,  contraction  of  the  ven- 
tricles, occlusion  of  the  auriculo-ventricular  valves,  and  opening  of 
the  sisrmoid  valves. 


Fig.   74. — The  Action  of  the  Tricuspid  Valve.      (Ciiauveau.) 

Pr,  Tracing  cf  the  variations  of  pressure  in  the  right  ventricle.  1,  Means 
first  sound  S,  Tracing  by  the  signal  magnet,  showing  the  action  of  the  valve, 
■which  by  its  movements  closes  and  opens  an  electric  current  to  the  signal 
magnet.  The  first  sound  (closure  of  the  auriculo-ventricular  valves)  is  simul- 
taneous with  the  beginning  of  the  ventricular  systole  and  it  produces  during  the 
first  sound   a  ra,pid  ascent  of  the   curve  of  ventricular  pressure. 

While  the  above  phenomena  are  synchronous  with  the  first 
sound,  yet  the  majority  of  them  are  believed  to  have  no  action  in 
producing  the  first  sound.  Thus,  the  sound  is  audible  in  a  heart 
from  before  which  the  chest-wall  has  been  removed,  so  that  precor- 
dial shock  is  not  the  source  of  the  sound. 

That  the  opening  of  the  sigmoid  (semilunar)  valves  is  not  of 
consequence  has  long  been  refuted  by  experiment. 

In  the  case  of  the  second  sound  we  just  learned  that  the  pro- 
duction of  it  was  due  to  the  closure  of  the  sigmoid  valves.  In  like 
manner  the  closure  of  the  auriculo-ventricular  valves  is  in  part  the 
cause  of  the  first  sound.  Wintrich,  by  means  of  proper  resonators, 
was  able  to  analyze  the  first  sound  and  so  distinguish  the  clear,  snappy 
valvular  component  of  this  so-called  solid  sound.  The  very  fact  that 
the  sound  is  low  and  booming  in  nature  demonstrates  the  fact  that 
there  must  be  some  other  component  entering  into  its  causation. 


224  PHYSIOLOGY. 

The  tension  and  vibration  of  the  chordae  tendinea?  are  factors 
in  producing  sound,  but  the  nature  of  it  is  similar  in  every  respect 
to  that  produced  by  valvular  vibration. 

Even  though  the  auriculo-ventricular  valves  and  their  chordae 
tendinese  be  destroyed  in  an  excised  heart,  yet  will  there  be  pro- 
duced a  feeble  sound  of  rather  low  pitch.  This  sound  is  believed  to 
be  produced  by  the  contraction  of  the  muscular  fibers  of  ventricular 
walls,  and  has  been  termed  ^^muscle-sound." 

Any  muscle  whatever,  during  its  contraction,  gives  rise  to  a  dull 
sound.  It  is  evident  then  that,  during  contraction  of  the  ventricle, 
this  same  phenomenon  must  occur  and  so  contribute  its  part  to  the 
production  of  the  first  sound. 

From  new  experiments  it  appears  that  the  role  of  the  muscular 
contraction  is  more  important  than  it  has  generally  been  thought  to 
be.  For  verification  of  this  the  following  experiment  seems  to  be 
decisive : — 

The  heart  is  exposed  in  a  dog  which  has  been  poisoned  with 
curare  and  in  which  artificial  respiration  has  been  maintained  dur- 
ing two  hours.  The  left  veritricle  is  cut  open  in  front  and  at  the 
back  with  scissors  along  the  intraventricular  partition.  The  incis- 
ions are  rapidly  lengthened  from  the  apex  toward  the  base  in  such 
a  manner  as  to  turn  completely  outside  all  the  ventricular  wall. 
This  portion  is  no  longer  held  to  the  rest  of  the  heart  except  by  the 
auricle. 

The  suspended  piece  of  ventricular  wall,  under  these  conditions, 
continues  to  contract  with  force  and  rhythm  for  some  seconds.  If 
the  stethoscope  be  applied  to  the  internal  face  of  the  stump,  it  per- 
mits us  to  hear  at  the  moment  of  each  contraction  a  sound  that  is 
exactly  like  the  one  which  had  been  perceived  in  the  nonmutilated. 
There  is,  however,  a  vast  difference  in  intensity,  the  sound  emitted 
from  the  experimental  heart-muscle  being  very  weak. 

The  contraction  of  the  auricles  is  not  considered  at  all  as  being 
a  factor  in  the  production  of  cardiac  sounds.  Eepeated  experiments 
have  proved  the  auricular  contractions  to  be  inaudible. 

Position  of  Valves  and  the  Areas  of  Audibility. — The  pulmonary 
and  tricuspid  of  the  right  side  lie  nearer  the  surface  than  the  aortic 
and  mitral  of  the  left. 

The  best  point  to  hear  the  pulmonary  valve  is  chiefly  behind 
the  third  left  costal  cartilage.  For  the  aortic  valve  it  is  behind  the 
left  half  of  the  sternum,  on  a  level  with  the  third  space.  For  the 
mitral  valve  it  is  behind  the  left  half  of  the  sternum,  on  a  level  with 


THE  CIRCULATION.  225 

the  fourth  and  upper  border  of  the  fifth  cartilage.  For  the  tricuspid 
valve,  behind  the  lower  fourth  of  the  sternum,  to  the  right  of  the 
iniddle  line  from  the  fourth  right  cartilage  to  a  point  behind  the 
junction  of  the  sixth  right  cartilage  to  the  sternum. 

Variations  in  Heart-sounds. — Increase  in  the  intensity  of  the 
first  sound  of  the  heart  is  indicative  of  a  more  vigorous  contraction 
of  the  ventricles,  with,  of  course,  greater  tension  of  the  auriculo- 
ventricular  valves. 

Increase  of  the  second  sound  denotes  a  higher  tension  in  the 
corresponding  large  arteries.  The  condition  is  usually  demonstra- 
tive of  overfilling  and  congestion  of  the  pulmonary  circuit.  With 
equal  intensity  the  muscular  sound  of  the  left  ventricle  is  appre- 
ciably longer  than  that  of  the  right. 

Weak  heart-sounds  are  indicative  of  a  feeble  action  of  the  heart 
and  usually  denote  degenerations  of  the  heart-muscle. 

The  Coronary  Arteries. — The  heart-muscle,  by  reason  of  its 
almost  constant  activity,  must  be  very  generously  supplied  with  blood 
to  insure  its  proper  nutrition.  In  it  are  found  a  system  of  arteries, 
capillaries,  and  veins,  known  as  the  coronary  vessels. 

The  arteries  going  to  the  heart-muscle  are  two  in  number:  the 
right  and  left  coronary.  They  are  the  first  branches  of  the  aorta,  and 
take  their  origin  just  above  the  level  of  the  free  margins  of  the  semi- 
lunar valves.  The  diameter  of  the  coronary  arteries  is  that  of  a 
crow's  quill.  From  these  main  vessels  there  proceed  numerous 
branches  which  dip  down  into  the  heart-substance,  dividing  and  sub- 
dividing as  they  go  until  a  system  of  capillaries  is  formed. 

The  effete  products  are  conveyed  to  the  general  circulatory  sys- 
tem by  the  coronary  vein,  which  empties  its  blood  into  the  right 
auricle. 

It,  with  its  branches,  is  provided  with  valves,  since  every  auri- 
cular systole  interrupts  the  venous  flow;  the  ventricular  contrac- 
tions, however,  accelerate  its  flow.  The  coronary  arteries  are  char- 
acterized by  their  very  thick  connective  tissue  and  elastic  intima, 
which  perhaps  accounts  for  the  frequent  occurrence  of  atheroma  of 
these  vessels. 

Ligature  of  the  coronaries  in  the  case  of  dogs  is  followed  by 
very  prompt  results,  because  of  the  sudden  anaemia  and  inability  of 
the  heart  to  rid  itself  of  its  metabolic,  decomposition  products. 
Within  two  minutes  the  cardiac  contractions  become  very  irregular, 
give  place  to  twitches,  and  then  all  movements  cease. 

In  those  cases  of  fatty  degeneration  where  alteration  of  the  cor- 

15 


226  PHYSIOLOGY, 

onary  vessel-walls  produces  the  condition  known  as  atheroma,  the 
symptoms  of  ligaturing  and  of  sudden  death  occur  because  of  the 
sudden  arrest  of  the  heart's  action. 

At  the  beginning  of  systole  the  blood  rushes  into  the  coronary 
arteries  in  the  same  fashion  that  it  does  into  other  arteries.  How- 
ever, later,  during  systole,  the  branches  of  the  coronary  arteries  are 
so  squeezed  by  the  strong  ventricular  contractions  that  the  passage 
of  the  blood  is  temporarily  obstructed  or  even  made  to  retrograde. 
Before  the  blood  can  recede  to  any  extent,  systole  has  ended  and  the 
blood  then  flows  along  as  before. 

It  has  also  been  found  that,  during  the  beginning  of  a  ventri- 
cular systole,  a  cut  into  the  coronary  artery  of  a  living  animal  causes 
a  spurt  of  blood  from  the  central  end  of  the  artery. 

A  shortening  of  the  diastolic  period  lessens  the  nutritive  supply 
to  the  heart.  Diastolic  distension  of  the  left  heart  by  "back  pres- 
sure" lessens  the  coronary  flow.  These  facts  are  of  much  practical 
import  in  diseases  of  the  heart. 

Frequency  of  the  Heart's  Action. — During  health  the  heart  acts 
so  smoothly  and  with  so  little  concern  on  our  part  that  there  is 
required  considerable  self-attention  before  any  differences  are  seen 
to  exist.  Its  action,  as  studied  from  the  throbbings  (pulse)  that  are 
exhibited  by  some  of  the  more  superficial  arteries,  and  each  of  which 
corresponds  to  ventricular  systole,  is  found  to  lie  in  very  close  sym- 
pathy to  the  other  great  functions  of  the  economy  and  is  accordingly 
influenced  by  them.  The  average  number  of  adult  beats  is  73  per 
minute.  Even  in  health  great  deviation  on  either  side  of  this 
standard  may  exist,  depending  upon  age,  sex,  size,  food  and  drink, 
3xercise,  posture,  etc.  That  age  and  sex  exercise  an  influence  upon 
the  frequency  of  the  heart's  movements  must  be  remembered  by  the 
clinician  when  making  his  diagnosis.  From  the  annexed  table  it  will 
be  noticed  that  just  before  birth  the  rate,  as  determined  by  the 
stethoscope,  is  very  high,  but  gradually  diminishes  until  very  old  age, 
when  there  is  a  slight  increase.  Sex  is  very  influential,  the  female 
heart  averaging  about  eight  beats  more  per  minute. 

It  has  been  noticed  that  the  rule  seems  to  be  that  smaller  ani- 
mals possess  a  greater  amount  of  neuro-muscular  activity  than  larger 
ones.  Among  human  beings  this  is  also  applicable,  shorter  people 
usually  having  a  pulse  that  is  a  trifle  more  rapid  than  taller  people. 
Idiosyncrasies  are  frequently  found  which  are  at  first  very  mislead- 
ing to  the  diagnostician.  Thus,  the  pulse  of  Napoleon  I  often  did 
not  exceed  40  beats  to  the  minute,  yet  he  was  perfectly  well.     After 


THE  CIRCULATION.  227 

each  meal  there  is  an  increase  of  from  5  to  10  beats,  while  following 
very  violent  exercise  the  figures  140  or  150  may  be  reached. 

During  health  there  is  found  a  nearly  constant  relation  existing 
between  the  number  of  heart-beats  and  of  respirations.  This  pro- 
portion is  four  heart-beats  for  every  single  respiration.  Even  when 
the  number  is  very  much  increased  from  violent  exercise  or  any  other 
cause,  the  proportion  still  remains  constant.  Pathological  conditions 
usually  alter  this  relation.     Landois  gives  the  following  results : — 

In  male  adults  the  pulse-rate  is  72,  in  females  80. 

Pulsations  per  Minute. 

Age  Malk. 

Foetal  130  to  140 

1  year  120  to  130 

2  years  105 

3  years  100 

4  years  97 

5  years  94 

10  years  90 

10  to  15  years  78 

15  to  50  years  70 

80  to  90  years  80 

Work  of  the  Heart. — When  a  force  produces  acceleration,  or 
when  it  maintains  motion  unchanged  in  opposition  to  resistance,  it 
is  said  to  do  worJc.  To  convey  an  impression  of  the  amount  of  work 
done  by  any  machine,  it  is  usual  to  express  its  efficiency  in  terms  of 
work-units.  This  is  a  comparatively  easy  task  when  attempted  in 
the  physical  world,  but  becomes  extremely  difficult  when  one  attempts 
to  express  in  terms  of  work-units  the  force  of  the  heart's  action. 
The  work  of  the  heart — central  pump,  that  it  is — is  so  hard  to 
reckon  in  view  of  the  ill-defined  data  that  we  are  able  to  obtain  as 
to  the  resistance  which  it  overcomes  and  from  the  fact  that  different 
portions  of  this  human  machine  are  known  to  exert  different  degrees 
of  force. 

Anatomical  differences,  then,  in  the  heart  musculature  permit 
the  conclusion  that  the  left  heart,  the  walls  of  which  are  thicker, 
has  more  force  than  the  right  heart.  It  is  reasonable  to  state  from 
these  premises  that  where  the  ventricular  walls  are  three  times 
thicker  in  one-half  of  the  heart  than  they  are  in  the  other,  that  one 
must  have  a  thrice  greater  systolic  force  than  the  other  half. 

The  work  of  the  heart  is  usually  expressed  in  kilogrammeters. 
A  kilogrammeter  is  equal  to  7.24  foot-pounds.  To  estimate  the 
work  of  the  heart  according  to  Dr.  Leonard  Hill,  the  mean  pressure 


228  PHYSIOLOGY. 

and  velocity  in  the  aorta  and  the  volume  of  blood  ejected  by  the 
ventricle  must  be  obtained. 

If  W  be  the  work  done  during  systole  of  the  left  ventricle  in 
gram  centimeters;  Q,  the  volume  of  the  output  in  cubic  centimeters; 
M,  the  mass  of  the  output  in  grams;  P,  the  specific  gravity  of  the 
blood  (.•.  M  =  PQ);  V,  the  mean  velocity  in  the  aorta;  H,  the 
mean  aortic  pressure  in  grams  per  centimeter;  g,  the  acceleration 
due  to  gravity  ^981  centimeters  per  second,  then 


MV 


2g 

.  W  =  QH+  ^^^' 


2g 

The  mean  aortic  pressure  may  be  put  down  as  12  centimeters 
of  mercury  (specific  gravity  of  mercury  =  13.5).  The  volume  of  the 
systolic  output  is  about  110  cubic  centimeters.  Substituting  these 
data  in  the  above  equation  one  obtains: — ■ 

1  05  X  110  X  33^ 

W=  110  +  12  +  13.5  +  ~ =  17.880  gram  cen- 

2  X  981  ^ 

timeters. 

If  in  the  case  of  the  right  ventricle  the  mean  pressure  in  the 

pulmonary  artery  be  taken  to  be  -1  centimeters  of  the  mercury, 

the  work  of  that  ventricle  will  be  one-third  of  that  of  the  left 

ventricle.     Thus,  the  total  work  of  each  systole  of  the  heart  will  be 

17,880  X  Vs  =  23,640  gram  centimeters,  and  the  total  work  of  the 

heart  will  be  per  day  about  24,000  kilogrammeters,  or  1000  kilo- 

grammeters  per  hour,  or  the  equivalent  of  about  V50  of  the  whole 

amount  of  heat  produced  in  the  body. 

INNERVATION  OF  THE  HEART. 

If  the  heart  be  removed  from  the  chest  or  all  of  its  nerves  be 
severed,  it  will  still  continue  to  beat  for  a  variable  time,  dependent 
upon  the  class  of  animal  operated  upon.  In  the  case  of  the  frog  and 
other  cold-blooded  animals  the  beating  of  the  heart  will  continue  for 
hours  under  favorable  conditions.  From  this  it  would  seem  that 
there  must  reside  within  the  heart  itself  some  mechanism  whereby 
the  rhythmical  movements  of  the  heart  are  maintained. 

Like  every  other  organ  of  the  body,  the  heart  receives  its  pro- 
per quota  of  nerve-supply,  through  whose  medium  are  conducted  cer- 
tain impulses  from  without  and  by  whose  influence  its  rhythm  may 


THE  CIRCULATION.  229 

be  altered.  Yet,  in  addition  there  would  seem  to  be  nerve-ganglia 
within  the  heart-substauce  which  behave  as  stimuli  to  the  heart  and 
so  maintain  its  ordinary  rhythmical  movements. 

Cardiac  Ganglia. — This  internal  mechanism  has  been  chiefly 
studied  in  the  frog,  where  there  exist  in  the  heart  three  distinct 
ganglia:  Remak's,  Bidder's,  and  von  Bezold's.  From  the  cells  of 
these  ganglia  there  are  discerned  numerous  small  fibers  which  form 
a  plexus  over  the  surface  of  the  auricles  and  upper  portion  of  the 
ventricles. 

Remah's  ganglion  is  seen  at  the  orifice  of  the  superior  vena  cava 
or  sinus  venosus.  Bidder's  is  located  at  the  jimction  of  the  auricles 
and  ventricles  in  the  auriculo-ventricular  groove.  Von  Bezold's 
ganglion  has  its  seat  in  the  interauricular  septum. 

The  heart  of  a  mammal  differs  from  that  of  an  amphibian  only 
in  that  there  are  several  groups  of  ganglia  in  the  mammals,  while 


I 

A, 

II 

^*^^^fc 

^-^   Yri 

^^^^T* 

s«v^^H 

fw 

^ 

^^m 

-YJv' 

ml^jb 

^^^Voi 

Fig.  75.— He; 

irt  of  the 

Frog.      ( Livox. ) 

I.  Anterior  view.  II.  Posterior  view.  A,  A,  Aortse.  Vc,  Superior  vena 
cava.  Or,  Auricle.  F,  Ventricle.  Ba,  Aortic  bulb.  «S'F,  Sinus  venosus. 
Tci,  Inferior  vena  cava.      Tb,  Hepatic  vein.      Vh,  Pulmonary  vein. 

but  one  exists  in  the  amphibians.  However,  these  several  ganglia 
of  the  mammal  are  believed  to  be  automatically  and  physiologically 
equivalent  to  the  homologous  single  ganglion  or  group  of  ganglia  of 
the  amphibian.     The  same  general  laws  may  be  applied  to  both. 

Cause  of  Cardiac  Rhythm. — The  rhythm  of  the  ventricle  is  a 
property  of  the  cardiac  muscle.  In  the  maintenance  of  this  rhythm 
the  nervous  system  does  not  intervene  except  as  an  ordinary 
excitant  of  muscle.  It  is  known  that,  if  the  apex  of  the  frog's  heart 
be  cut  away,  it  is  then  separated  from  all  ganglia.  The  excised  por- 
tion does  not  beat  spontaneously,  while  the  rest  of  the  heart,  the 
auricles  and  the  base  of  the  ventricles,  continue  their  rhythmical 
action.  Thus  it  seems  that  the  ventricles  normally  contract  under 
the  persuasion  of  irritations  which  arise  in  them  from  the  cardiac 
ganglionic  cells. 


230  .  PHYSIOLOGY. 

If  now  the  isolated  and  immovable  portion  of  the  heart  be 
placed  under  a  cardiograph  and  subjected  to  opening  of  the  induc- 
tion current,  there  will  result  a  pulsation  from  each  isolated  induc- 
tion shock. 

It  is  a  remarkable  fact  that,  if  this  same  excised  portion  be 
excited  by  frequent  breaks  (at  least  thirty  per  second),  the  muscle 
beats  rhythmically.  Ordinary  striped  muscle  responds  to  isolated  and 
separate  breaks  of  the  induction  current  by  manifesting  isolated 
contractions.     Heart-muscle  cannot  be  tetanized. 

Hence  this  observation  would  force  us  to  the  conclusion  that 
the  heart's  rhythm  does  not  depend  upon  the  ganglionic  cells  of  the 
heart.  The  rhythm  is  the  property  of  the  cardiac  muscle  to  react 
to  the  frequent  excitations  which  it  receives. 

In  this  respect  cardiac  muscle  is  completely  differentiated  from 
ordinary  striated  muscle.  It  is  a  mistake  to  seek  to  make  the  rhyth- 
mical property  of  the  cardiac  muscle  a  property  of  ordinary  muscle. 

Theory  of  Cardiac  Rhythm. — The  heart  is  not  equally  excitable 
during  rest  and  during  action ;  it  is  less  excitable  during  action  than 
during  waning  action;  that  is,  during  the  beginning  than  during 
the  end  of  systole.  The  comparative  want  of  excitability  is  so 
marked  during  the  commencement  of  systole  that  this  period  has 
been  called  the  refractory  period. 

The  auricles  and  ventricles  do  not  receive  excitations  except 
during  and  at  the  end  of  diastole,  because  of  the  refractory  phase 
during  cardiac  contraction.  It  is  during  diastole  that  the  cavities 
of  the  heart  possess  greatest  excitability.  At  the  end  of  general 
diastole  the  auricles  and  ventricles  are  full  of  blood,  particularly  the 
auricles. 

By  reason  of  this  blood-distension  the  auricles  become  excited 
and  contract.  The  blood  is  rushed  into  the  ventricles,  dilating  them 
to  their  maximum.  From  distension  produced  in  them  and  also 
from  ganglionic  impulses  which  were  not  efficacious  except  at  this 
moment,  the  ventricles  are  made  to  contract  in  their  turn. 

With  each  cardiac  cycle  the  same  phenomena  are  manifested, 
the  result  being  a  rhythmical  action  of  the  heart. 

The  warm-blooded  heart  increases  its  pulsations  with  rise  of 
temperature  and  decreases  them  correspondingly  with  fall  of  tem- 
perature. The  temperature  does  not  act  through  the  endocardium, 
but  directly  upon  the  muscle  itself  or  its  ganglia. 

Direct  irritation  of  the  surface  of  the  ventricle  with  tetanizing 
currents  of  electricity  shows  a  marked  change  in  the  rhythm.     Upon 


THE  CIRCULATION. 


231 


the  human  heart  the  constant  current  calls  out  an  acceleration  of 
the  heart,  while  an  induction  current  is  without  effect.  Hence,  in 
apparent  death  the  proper  current  to  employ  to  stir  up  the  heart  is 
the  constant  current. 

Numerous  experiments  have  been  performed  upon  the  hearts  of 
animals  (the  frog  chiefly)  for  determihing  the  causes  and  means  of 
control  of  the  rhythmical  movements  of  the  heart.  The  experi- 
ments consist,  for  the  most  part,  of  ligaturing  various  portions  of 
the  heart,  and  are  performed  by  tightening  and  then  relaxing  the 
ligature  so  that  the  physiological  connection  is  destroyed,  while  its 
anatomical  and  mechanical  functions  are  still  intact.  The  most 
important,  as  well  as  best  known,  of  the  ligature  experiments  is  the 
one  known  as : — 


A.  Ligature  below  the  auriculo-ventricular  groove  (L) ;  the  sinus  venosus 
(3)  and  the  auricles  (1)  continue  to  beat,  but  the  apex  of  the  isolated  ventricle 
is  arrested. 

B.  Ligature  of  L  to  sinus  (3),  which  continues  its  rhythmical  beats;  1 
and  2  are  arrested  in   diastole  (seventh  experiment  of  Stannius). 

C  After  the  ligature  (L)  as  in  B,  a  second  ligature  (L')  is  placed  around 
the  auriculo-ventricular  groove;  the  ventricle,  which  was  originally  arrested, 
after  some  rhythmical  contraction,  is  again  arrested  (tenth  experiment  of 
Stannius). 


Staxxius's  Experiment. — If  the  sinus  venosus  of  the  frog's 
heart  be  separated  from  the  auricles  by  the  application  of  a  ligature, 
then  the  auricles  and  ventricles  will  remain  quiet  in  diastole,  while 
the  veins  and  the  remainder  of  the  sinus  continue  to  beat.  If  a 
second  ligature  be  applied  at  the  junction  of  the  auricles  and  ven- 
tricle, the  usual  sequence  is  for  the  ventricle  to  begin  to  beat  again 
while  the  auricles  continue  to  remain  in  their  diastolic  rest.  Though 
the  two,  sinus  venosus  and  ventricle,  continue  to  beat,  their  motion 
is  not  rhythmical,  the  ventricular  movements  being  considerably 
slower.     In  every  case  the  quiescent  portion  can  be  made  to  give 


232  PHYSIOLOGY. 

single  contractions  by  stimuli,  either  mechanical  or  electrical.  Thus, 
when  the  ventricle  remains  quiet  after  the  first  ligature,  it  may  be 
made  to  give  single  contractions  by  pin-pricks. 

To  explain  the  experiment  of  Stannius  it  has  been  asserted  that 
Eemak's  and  Bidder's  ganglia  are  motor  and  von  Bezold's  is  inhibi- 
tory; that  the  motor  influence  of  Eemak's  and  Bidder's  is  greater 
than  the  inhibitory  influence  of  von  Bezold's;  hence,  in  the  absence 
of  all  ligatures,  the  heart  beats.  That  the  motor  power  of  Bidder's 
is  less  than  the  inhibitory  power  of  von  Bezold's;  consequently,  the 
first  ligature  cutting  ofl:  the  motor  power  of  Eemak's,  the  auricle 
and  ventricle  stand  quiescent,  while  after  the  second  ligature,  cut- 
ting off  also  the  inhibition  of  von  Bezold's  ganglia,  the  ventricle, 
actuated  by  Bidder's  ganglia  alone  and  unopposed,  again  commences 
to  beat. 

According  to  Gaskell  and  Englemann,  the  nerve-ganglia  do  not 
play  any  part  in  the  movements  of  the  frog's  heart.  According  to 
their  ideas  the  sinus  sends  out  impulse-waves  through  the  muscular 
structure  of  the  heart.  When  the  first  Stannius  ligature  is  applied 
it  blocks  the  waves  running  from  the  sinus  to  the  right  auricle. 
Here  the  sinus  continues  beating,  but  the  remainder  of  the  heart  is 
quiet.  If,  now,  you  tie  a  ligature  in  the  auriculo-ventricular  groove 
of  this  quiescent  heart,  then  the  ventricle  beats.  The  ligature  or 
compressor  at  this  point  is  said  to  stimulate  the  ventricle. 

His  has  discovered  a  bundle  of  muscular  fibers  which  run  from 
the  posterior  part  of  the  interauricular  septum  into  the  intraventri- 
cular septum,  and  it  is  held  to  be  a  pathway  of  myogenic  impulses 
from  the  auricle  to  the  ventricle.  When  this  bundle  of  fibers  is 
clamped  in  animals,  the  ventricle  beats  with  a  slower  rhythm  and 
one  entirely  independent  of  the  auricles.  In  the  Stokes-Adams  dis- 
ease we  have  a  similar  block  in  the  heart,  where  the  rhythm  of  the 
ventricle  is  independent  of  the  auricle;  the  ventricles  may  be  beat- 
ing 37  per  minute  and  the  auricles  90.  These  facts  favor  the  myo- 
genic theory  of  cardiac  contractions.  Kronecker,  however,  has  liga- 
tured this  bundle  of  His  and  has  never  seen  the  pulsations  of  the 
heart  interrupted  or  modified,  and  he  states  that  it  does  not  enjoy 
any  role  in  the  conduction  of  motor  impulsions  from  the  auricle  to 
the  ventricle,  but  that  they  take  place  only  through  the  nerve-ele- 
ments. 

Tawara  holds  that  the  cells  in  the  bundle  of  His  are  not  the 
ordinary  muscular  fibers  of  the  heart,  but  the  variety  of  cardiac  mus- 
cle which  has  been  called  Purkinje  cells  or  fibers.     He  also  found 


THE  CIRCULATION. 


233 


a  nervous  network  in  this  bundle.  Dr.  Alfred  Stengel  discovered 
an  atheromatous  lesion  in  the  bundle  of  His  in  a  case  of  Stokes- 
Adams  disease. 

Dogiel  and  Archangelsky,  in  a  frog's  heart,  have  extirpated  the 
ganglia  of  Bidder,  the  intraventricular  ganglia,  and  the  ganglion 
cells  and  nerves  which  lie  about  the  auriculo-ventricular  groove,  and 
found  that  the  ventricle  lost  the  power  to  rhythmically  contract, 
although  its  muscle  and  nerves  were  retained  up  to  the  ganglion 


Fig.  77. — Cardiac  Plexus  and  Stellate  Ganglion  of  the  Cat.      (Landois.) 

B,  Right.  L,  Left  (X  li/2)-  t,  Vagus.  2',  Cervical  sympathetic  and  In 
the  annulus  of  Vieussens.  2,  Communicating  branches  from  the  middle  cer- 
vical ganglion  and  the  ganglion  stellatum.  2",  Thoracic  sympathetic.  3,  Re- 
current laryngeal.  4,  Depressor  nerve.  5,  Middle  cervical  ganglion.  5',  Com- 
munication between  5  and  the  vagus.  6,  Ganglion  stellatum  (first  thoracic 
ganglion).  7,  Communicating  branches  with  the  vagus.  8,  Nervus  accelerans. 
8,  8',  8",  Roots   of   accelerans.      9,  Branch    of   ganglion   stellatum. 

cells,  which  had  been  removed.  In  such  a  heart,  robbed  of  its 
ganglion  cells,  the  law  of  Bowditch,  that  a  minimal  irritation  is  at 
the  same  time  a  maximal  one,  fails,  for  the  cardiac  muscle  gave  vary- 
ing heights  of  contraction  with  varying  strength  of  the  electrical 
current. 


234 


PHYSIOLOGY. 


Extracardiac  Nervous  System. 

The  extracardiac  nervous  system  is  composed  of  llie  cardiac 
branches  of  the  vagus,  together  with  the  cardiac  branches  of  the 
sympathetic. 

The  Vagus. — The  superficial  origin  of  this  nerve  is  from  the 
groove  between  the  inferior  olive  and  the  restiform  body.  It  leaves 
the  skull  by  passing  through  the  middle  compartment  of  the  jugular 
foramen,  presenting,   immediately   after   its   exit,   an   enlargement 


Fig.  78. — Course  of  Vagus  Nerve  in  Frog.      (Stirling.) 

SM,    Submentalis.      LU,    Lung.      V,    Vagus.      OP,    Glosso-pharyngeal. 
Hypoglossal.       L,  Laryngeal.       I'H,  SH,  Gil,   OH,    Petro-,    sterno-,    genio- 
omo-    hyoid.      EG,  Hypoglossus.       H,  Heart.       BR,  Brachial    plexus. 


and 


known  as  the  gangliform  plexus.  The  accesory  portion  of  the  spinal 
accessory  nerve  joins  this  ganglion,  while  the  hypoglossal  nerve 
winds  around  it  in  a  spiral  manner. 

As  has  been  previously  stated,  the  immediate  cause  of  the  rhyth- 
mical contractions  of  the  heart  lies  in  the  protoplasm  of  the  muscle- 
cells  themselves,  but  that  the  rate  and  force  of  its  beats  are  influenced 
by  impulses  reaching  it  through  the  central  nervous  system.  The 
effects  of  these  impulses  are  twofold:  inliihition,  or  diminution  in 
the  rate  or  force  of  the  heart-beat,  and  acceleration,  or  increase  in 


THE  CIRCULATION. 


235 


the  rate  or  force.  Both  the  inhibitory  and  accelerator  centers  are 
located  within  the  medulla,  fibers  from  which  leave  the  cranium  and 
reach  the  heart.  Of  these  efferent  fibers  of  the  vagus,  the  inhibi- 
tory ones  are  most  prominent  and  come  from  the  spinal  accessory. 

However,  there  are  accelerator  fibers  which  take  their  origin  in 
the  medulla  oblongata  and  then  descend  in  the  spinal  cord.  They 
emerge  by  the  anterior  roots  to  the  stellate  ganglion  or  first  thoracic, 
then  proceed  by  the  annulus  of  Vieussens  to  the  inferior  cervical 
ganglion  of  the  sympathetic,  and  then  to  the  heart-muscle. 

Knowledge  of  the  presence  of  inhibitory  fibers  in  the  vagus  is 
due  to  the  investigation  of  the  Weber  brothers,  who,  about  fifty 
years  ago,  demonstrated  their  presence  in  the  vagus  of  the  frog. 
They  showed  that  stimulation  of  one  or  both  produces  slowing  or 


(llUl/l/lil/lilil^^ 


iumm 


Fig.  79.- 


-Traeing  by  Lever  Attached  to  Frog's  Heart  on  Stimulation 
of  the  Pneumogastric  Nerve.     (Foster.) 


a-b   shows    time    of   stimulation    by    electricity.     As   ttie   tracing   shows,    the 
heart's  movements  were  arrested   for   some  time. 


complete  stoppage  of  the  beats  of  the  heart.  Stimulation  not  only 
inhibits  the  heart's  action,  but  also  modifies  it  in  this,  that  the  force 
of  the  contraction  and  the  income  and  output  of  the  ventricle  are 
diminished.  The  number  of  ventricular  and  auricular  beats  are  not 
in  unison,  both  being  less  frequent. 

It  makes  no  difference  whether  one  irritates  the  center  of  the 
pneumogastrics,  their  trunk,  or  peripheral  ends  within  the  heart,  the 
same  result  follows:  there  is  a  diminution  in  the  number  of  the 
heart-beats.  A  tap  upon  the  abdominal  wall  is  able  to  throw  the 
pneumogastric  into  greatly  increased  action;  so  that  the  heart  is 
often  stopped  and  death  ensues.  In  this  case  the  sympathetic 
nerves  of  the  solar  plexus  convey  the  impression  up  the  spinal  cord 
to  the  center  of  the  pneumogastric  in  the  medulla.  From  the  medulla 
the  impulse  is  sent  down  the  inhibitory  fibers  of  the  pneumogastric. 


236  PHYSIOLOGY. 

which  causes  arrest  of  the  heart.  The  arrest  always  occurs  in  diastole, 
never  in  systole. 

All  of  the  sensory  nerves  of  the  body  have  a  reflex  relation  to 
the  pneumogastrics.  Even  pinching  the  skin  of  some  fishes  is  suffi- 
cient to  stop  the  heart.  Irritation  of  the  branches  of  the  fifth  nerve 
in  the  rabbit  by  ether  and  other  vapors  can  stop  the  heart.  There 
are  reasons  to  believe  similar  results  can  occasionally  be  obtained  in 
man. 

Swallowing  Fluids. — Experimenters  have  demonstrated  that 


Fig.  80. — Arrest  of  the  Heart  of  a  Rabbit  by  Irritation  of  the  Peripheral 
End  of  the   Pneumogastric   in   the   Neck.      (  Gley.  ) 

PC,   Carotid  pressure   equals   12   centimeters   of   mercury.     E,    Excitation  of 
the  nerve  by  an  induction  current.     T,  Time  every  2  seconds. 

swallowing  interferes  with  or  even  may  abolish  for  a  short  time  the 
cardio-inhibitory  action  of  the  vagus.  By  reason  of  this  the  pulse- 
rate  is  greatly  increased.  Sipping  a  wineglassful  of  water  will  raise 
the  pulse-count  30  per  cent.  In  this  way  water  can  be  made  to 
behave  as  a  powerful  cardiac  excitant.  The  course  of  the  impulse 
is  along  afferent  fibers  of  the  nerves  supplying  the  oesophagus  to  the 
cardio-inhibitory  center,  whose  tonus  is  reduced. 

Stimulation  of  the  vagus  always  produces  the  same  result — inhi- 


THE  CIRCULATION. 


237 


bition — no  matter  at  what  point  in  its  course  the  nerve  be  stimu- 
lated. 

If  the  pneumogastries  be  divided  in  the  neck  the  heart  runs 
with  great  rapidity.  This  is  due  to  the  removal  of  the  inhibitory 
power,  which  comes  from  the  center  located  within  the  medulla.  A 
brake,  as  it  were,  is  taken  from  the  heart,  so  that  all  restraint  is 
removed. 

Inhibition  is  not  perceived  immediately  after  the  application  of 
the  stimulus.  There  is  present  a  distinct  latent  period  which  pre- 
cedes the  inhibitory  effects.     Various  conditions  may  modify  the 


Fig.  81. — Irritation  of  Nerviis  Depressor  in  a  Rabbit,  Causing  a  Fall 
of  Arterial  Tension.      (Gley.  ) 

PC,   Carotid  pressure.     E,   Time  of  irritation  of  nerve  by  the  induced  cur- 
rent.     T,  Time    recorded    every    two    seconds. 


length  of  this  period,  but  the  average  duration  is  one  or  two  beats. 
The  stimulus  is  applied  to  either  side,  though  the  right  vagus  seems 
to  be  more  susceptible ;  when  the  stimulus  is  strong  enough  to  cause 
complete  stoppage,  this  condition  is  the  result  of  lengthening  the 
diastole,  the  most  usual  occurrence. 

Peculiarities. — Some  of  the  points  of  peculiarity  of  the  vagus 
and  its  action  are:  1.  The  heart  is  arrested  in  diastole;  so  that  the 
slowing  depends  upon  the  period  of  diastole.  2,  The  irritation  of 
one  nerve  alone  acts  upon  the  two  sets  of  inhibitory  ganglia  in  the 
heart  by  reason  of  association  fibers.  3.  After  the  arrest  of  the 
heart  by  excitation  of  the  vagus,  the  heart  begins  its  contractions 
first  in  the  auricles. 


238 


PHYSIOLOGY. 


Afferent  Nerve  of  the  Heart  (Depressor  Nerve  of  Ludwig 
and  von  Cyon.) — This  nerve  in  the  rabbit  usually  arises  from  two 
branches,  one  from  the  trunk  of  the  vagus  and  the  other  from  the 
superior  laryngeal.  It  ends  in  the  heart,  and,  according  to  some,  in 
the  aorta's  origin.  It  is  found  in  man  and  other  animals.  When 
its  central  end  is  stimulated,  there  is  a  fall  of  arterial  tension  to 
about  half  its  former  level.  After  the  stimulation  is  arrested,  the 
tension  returns  to  normal.     With  this  fall  of  arterial  tension  the 


|V      JMD 


Fig.  82. — Scheme  of  the  Cardiac  Nerves  in  the  Rabbit.      (Landois.) 

P,  Pons.  MO,  MeduUa  oblongata.  Tag,  Vagus.  SL,  Superior  Laryngeal. 
IL,  Inferior  laryngeal.  SC,  Depressor  or  superior  cardiac  brancii.  IL-H, 
cardio-inhibitory.     H,  Heart,      a,   a.  Accelerator  fibers.     S,  Cervical  sympathetic. 


beats  of  the  heart  are  slowed;  but  if  the  vagi  are  divided,  there  is 
no  change  in  the  frequency  of  the  heart,  which  shows  that  the 
lessening  of  the  number  of  heart-beats  is  due  to  stimulation  of  the 
cardio-inhibitory  center.  Even  after  curarization,  irritation  of  the 
central  end  of  the  depressor  lowers  the  arterial  tension.  If  the 
splanchnics  are  previously  divided,  stimulation  of  the  depressor  has 
hardly  any  effect.  After  an  injection  of  pyocyanin,  which  para- 
lyzes the  vasodilator  centers,  irritation  of  the  depressor  does  not 
lower  arterial  tension. 


THE  CIRCULATION. 


239 


Porter  and  Beyer  have  shown  that  it  dilates  the  arterioles 
throughout  the  body,  and  especially  those  blood-vessels  innervated 
by  the  splanchnics.  Excessive  repletion  of  the  heart  stimulates  the 
endings  of  the  depressor  nerve  in  the  heart.  These  afferent  impulses 
inhibit  the  main  vasomotor  center  and  permit  the  arterioles  to 
dilate,  and,  opening  the  flood-gates,  thus  relieve  the  systolic  strain 
of  the  muscular  fibers  of  the  heart.  The  depressor  nerve  is  not  in 
constant  action  and  is  not  easily  fatigued. 


Sup-,  lar.  n. 


Depressor 


S.C.C. 


--Sym^. 


,.. -Vagus 


Vagus 


Sup-,  lar.  n.-j 


...  Sup^.  Cerv.  Gang 
-  Depressor 


Cerv.  symp.  n. 


— Vago.  symp 


RABBIT 


DOG 


Fig.  83. — Diagram  of  the  connections  of  the  Depressor  Nerve  in  the 
Rabbit  and  Dog,  according  to  Cyon.  It  will  be  noticed  that  in  the  lat- 
ter animal  the  depressor  nerve  runs  in  the  vagus  trunk  for  the  greater 
part  of  the  course.      (Starling.) 


It  has  been  stated  that  the  depressor  nerve  acts  like  a  safety- 
valve  to  the  heart. 

Von  Cyon  has  shown  that  iodothyrin  augments  the  irritability 
of  the  depressor  nerve. 

The  depressor  is  greatly  called  into  play  in  the  heart  of  the 
bicycle-rider,  where  the  abdominal  reservoir  of  blood  is  compressed 
by  the  active  abdominal  muscles,  and  the  blood  is  driven  into  the 
thoracic  cavity  and  the  heart  is  swollen  with  blood.  The  depressor 
cannot  well  dilate  the  abdominal  vessels,  for  they  are  compressed  in 
bicycle-riding  by  the  violent  compression  of  the  muscles  of  the 
abdomen. 


240 


PHYSIOLOGY. 


Fig.  84. — Schema  of  Innervation  of  the  Heart  of  a  Dog.      (Mobat.  ) 

gg.ca,  Cardiac  ganglia  in  which  the  cardiac  nerves  terminate,  gg.ci.  Inferior 
cervical  ganglion,  g.cs,  Superior  cervical  ganglion,  gg.pl,  Plexiform  ganglion. 
sym.th.  Thoracic  sympathetic.  an.Ti,  Ansa  Vieussenii.  pn.g,  Pneumogastric. 
n.re.  Vertebral  nerve.  Vag.symp.,  Vago-sympathetic.  sym.c.  Cervical  sympa- 
thetic, sym.cr,  Prolongation  of  the  sympathetic  in  the  skull.  6",  First  cervical 
pair.  D\  First  dorsal  pair.  X,  Origin  of  the  pneumogastric.  XI,  Bulbar  origin 
of  the  spinal  accessory. 


Accelerators. — When  they  are  irritated  they  not  only  accelerate 
the  beat  of  the  heart,  but  also  increase  the  force,  causing  a  greater 
output  of  blood. 


THE  CIRCULATION.  241 

The  accelerators  apparently  have  less  powerful  functions,  for 
when  the  inhibitors  and  they  are  simultaneously  irritated  the  effect 
is  inhibition.  The  phenomenon  is  less,  however,  than  if  the  same 
inhibitors  had  been  stimulated  by  themselves.  Aside  from  their 
great  and  primary  differences  as  to  the  effects  produced,  the  acceler- 
ators differ  in  that  they  require  a  greater  intensity  of  stimulus  to 
produce  any  results ;  also  in  that  a  comparatively  long  latent  period 
precedes  every  effect.  In  every  respect  the  accelerators  seem  to  be 
directly  opposite  to  the  inhibitors.  They  are  the  antagonists  of  the 
inhibitors. 

When  the  accelerator  fibers  are  divided,  the  rhythm  of  the  heart 
remains  unchanged.  This  proves  that  the  accelerator  center  is  not 
constantly  in  a  state  of  tonic  excitement.  When,  however,  the 
peripheral  ends  of  the  accelerators  are  stimulated  by  a  faradic  cur- 


j^"      £4-        ,,,'.          28         ^^.           32         J.          0<i         ^..           27          ,„  •■          ^// 

■|   ,   '       '       ■       -      1       P--' — 1 r— 1 ! : r     -r-    j—   ,    -\ 1 [ j r i r--i — -|      t      t— -i r—\.. 

Fig.  85. — Curve  of  Blood-jiressure  in  the  Cat,  recorded  by  a  mercury 
manometer,  showing  the  increase  in  frequency  of  heart-beat  from  excita- 
tion of  the  augmentor  nerves.      (From  Howell.) 

The  curve  reads  from  right  to  left.  The  augmentor  nerves  were  excited 
during  thirty  seconds  between  the  two  stars.  The  number  of  beats  per  tea 
seconds  rose  from  24  to  33   (Boehm,   1875,   p.   258). 

rent,  the  amount  of  blood  ejected  from  the  heart  is  increased  and 
the  arterial  tension  is  necessarily  raised.  The  force  of  the  contrac- 
tion of  the  auricles  and  ventricles  is  also  increased.  Hence,  some 
believe  the  accelerators  contain  both  accelerator  and  augmentor 
fibers. 

LudM'ig  holds  that  the  reduction  of  blood-pressure  in  the  capil- 
laries of  the  brain,  but  particularly  those  of  the  medulla,  excites  the 
accelerators.  Exhilarating  emotions  and  diminished  blood-pressure 
also  throw  them  into  activity.  Oxygen  is  an  accelerator.  When 
the  heart  beats  rapidly  from  any  agreeable  cause,  or  one  feels  "light 
at  heart,"  the  manifestation  is  due  to  the  influence  of  the  acceler- 
ator fibers  on  the  heart. 

The  sympathetic  fibers  which  pass  to  the  heart  are  nonmedul- 
lated,  having  lost  their  medulla  in  the  various  ganglia  through  which 

16 


242  PHYSIOLOGY. 

they  pass.  In  this  respect  they  arc  in  direct  antagonism  to  the 
inhibitory  fibers,  whose  course  can  be  ascertained  by  the  histologist 
in  his  microscopical  study  of  the  pneumogastric.  The  augmentor 
center  is  in  the  medulla  oblongata. 

Thus,  the  heart  is  controlled  by  two  nerves  whose  functions  are 
diametrically  opposite  in  character.  They  establish  a  system  of 
"check"  upon  one  another,  each  normally  preventing  extremes  in 
the  action  of  the  other. 

Influence  of  Drugs. — Because  of  the  complicated  action  of  vari- 
ous drugs  upon  the  heart,  many  observers  are  led  to  believe  that 
there  are  various  internal  mechanisms  of  the  heart  upon  which  these 
substances  act.  Besides  acting  upon  the  muscular  tissue,  some  are 
found  which  exert  influences  upon  the  intracardiac  ganglia.  The 
two  drugs  that  are  most  familiar  to  the  physiologist  and  those  with 


Fig.  86. — Increase  in  the  Force  of  the  Ventricular  Contraction 
(curve  of  pressure  in  riglit  ventricle)  from  stimulation  of  augmentor 
fibers.      (Howell.) 

There  is  little  or  no   change  in  frequency    (Frauck,   1S90,  p.  819). 

which  he  is  most  engaged  in  performing  his  experiments  are  atropine 
and  muscarine.  Their  actions  are  both  nervous.  Thus,  atropine 
paralyzes  the  post-ganglionic  fibers,  thereby  giving  the  accelerators 
full  sway,  the  consequence  being  augmentation  of  the  heart's  beats. 
On  the  other  hand,  muscarine  stimulates  permanently  the  inhibitory 
ganglia,  so  that  the  heart-beats  are  slowed,  or,  if  the  dose  be  large 
enough,  complete  arrest  of  heart  movement  follows. 

If  a  frog's  heart  be  excised  and  placed  in  a  suitable  vessel  and 
a  few  drops  of  a  very  dilute  solution  of  muscarine  be  placed  upon 
it,  its  beats  will  soon  cease  and  it  will  continue  quiescent  as  long  as 
the  muscarine  remains  upon  it.  When  the  muscarine  is  removed 
and  atropine  applied  to  the  heart,  its  regular  beats  manifest  them- 
selves within  a  short  time.     Pilocarpin  also  stimulates  the  cardio- 


THE  CIRCULATION. 


243 


inhibitory  ganglia  and  slows  the  heart.  Atropine  removes  tliis  and 
the  heart  beats  faster.  Nicotine  in  small  doses  paralyzes  the  ends  of 
the  preganglionic  fibers  of  the  cardiac  parasympathetic  ganglia. 

Some  drugs  produce  results  by  their  effects  upon  the  heart- 
muscle  alone,  either  stimulating  or  depressing  the  same.  Thus,  the 
muscular  contractions  are  rendered  more  forceful  while  the  rate  is 
uninfluenced  by  the  action  of  digitalis,  strophanthus,  etc.  The  mus- 
cular contractions  are  depressed  by  veratrum,  aconite,  etc. 

In  addition  to  drugs  influencing  the  heart's  action  by  effects 
upon  its  muscle  and  ganglionic  nerve  terminations,  some  exert  an 
influence  upon  the  vagus  center  in  the  medulla  oblongata.  Thus, 
aconite,  digitalis,  and  adrenalin,  by  stimulating  this  center,  produce 
a  slowing  of  the  heart-beats. 

Some  heart-poisons  in  small  doses  diminish  the  heart's  action 
and  in  large  doses  usually  accelerate  its  movements;  or  the  con- 
verse may  be  the  truth  with  regard  to  the  doses  of  other  drugs. 


-^' 


I  i  I  N  I 


Fig.  87. — Staircase  Contractions  of  a  Frog's  Ventricle  in  Response 
to  a  Series  of  like  Stimuli,  written  on  a  regularly  revolving  drum  by 
the  float  of  a  water  manometer  connected  with  the  chamber  of  the  ven- 
tricle.    (Howell,  after  Bowditch.) 

The  record  is  to   be   read   from   right   to   left. 


Stannius  Heart. — If  in  a  frog's  heart  the  Stannius  ligature  be 
applied  around  the  heart  at  the  junction  of  the  sinus  with  the 
auricle,  the  auricle  and  ventricle  stand  still  in  diastole,  and  it  is  then 
called  a  Stannius  heart. 

Minimal  Stimulus  Causes  Maximal  Contraction. — If  you  excite 
once  a  minute  the  apex  of  a  Stannius  heart  with  induced  current  of 
necessary  intensity,  commencing  with  currents  too  weak  to  cause  a 
contraction,  it  will  be  found  that  finally  the  heart  contracts.  If  the 
current  is  augmented,  still,  a  contraction  ensues  of  the  same  height 
as  at  first.  The  height  of  the  contraction  is  independent  of  the 
intensity  of  the  electric  current.  In  other  words,  with  very  weak 
induction  currents  the  heart  either  does  not  contract,  or,  if  it  con- 
tracts, does  its  best.  With  skeletal  muscle,  increasing  the  strength 
of  the  electrical  stimulus  increases  the  height  of  contraction. 


244  PHYSIOLOGY. 

Staircase  Contraction  of  Bowditch. — In  a  Stanniused  heart 
where  the  ventricle  is  quiescent,  single  induction  shocks  of  a  con- 
stant strength,  applied  at  intervals  of  five  seconds,  will  produce  con- 
tractions. It  is  found  that  for  the  first  five  beats  the  contractions 
become  longer  with  each  irritation.  After  that  they  remain  about 
the  same.  This  is  called  the  staircase  phenomena  of  cardiac  muscle. 
This  is  also  seen  in  skeletal  muscle. 

Refractory  Period  of  the  Heart. — Marey  observed  that  the 
irritability  of  the  heart  to  weak  electrical  currents  decreased  during 
systole  and  increased  during  diastole.  Thus,  a  weak  induction  cur- 
rent applied  to  a  heart  during  systole  does  not  call  out  a  contraction, 
but  only  during  diastole. 


Fig.  88. — Refractory  Period  of  Heart-muscle  of  Frog,  with  Com- 
pensatory Pause. 

Shock  applied  at  A  is  effective,  causing  an  extra-contraction  followed  by  a 
compensatory  pause.    At  B,  stimulation  is  ineffective. 


AVhen  a  stimulus  is  thrown  in  at  any  point  between  the  maxi- 
mum of  the  systole  and  the  beginning  of  the  next  contraction,  it 
causes  what  is  denominated  an  extra-contraction,  which  is  followed 
by  a  longer  pause  than  usual,  the  compensating  pause,  which  reha- 
bilitates the  rhythm  so  that  the  succeeding  contraction  falls  in  the 
curve  where  it  would  have  fallen  had  there  been  no  extra-contraction. 

The  irritability  being  much  lowered  from  the  decomposition  of 
energy-holding  compounds  is  the  cause  of  no  contraction  when  the 
stimulus  is  thrown  in  during  systole. 

Nutrition  of  the  Heart. — Kronecker  made  a  double  perfusion 
cannula ;  on  one  side  the  nutrient  fluid  enters  the  ventricle  of  a  frog 
tied  on  it,  whilst  on  the  other  side  it  passes  out. 

Eabbits'  serum  delayed  the  stoppage  of  a  beating  heart,  whilst 


THE  CIRCULATION. 


245 


hearts  supplied  with  normal  saline  ceased  to  beat  sooner  than  hearts 
left  empty. 

In  the  blood  are  found  certain  salts  which  are  necessary  to  keep 
the  frog's  ventricle  pulsating. 

An  isotonic  solution  (0.7  per  cent,  of  sodium  chloride)  is  neces- 
sary to  keep  the  heart  beating;  but  to  keep  the  contractions  going, 
calcium  must  be  added,  to  prevent  the  calcium  leaving  the  cardiac 
tissue.  But  the  addition  of  calcium  leads  to  a  persistent  contrac- 
tion of  the  muscle  of  the  heart.  But  if  now  you  add  potassium  the 
heart  contractions  become  normal,  showing  an  antagonistic  action 
between  potassium  and  calcium. 


Hefraetorif"  |         "rxcitable" I'erioci 
Period         ! 


Fig.  S9. — To  Illustrate  the  Varying  Excitability  of  the  Frog's  Heart 
at  Different  Periods  of  Systole  and  Diastole.      (Waller.) 

The  excitability  is  lowest  during  the   first  half  of  systole,   greatest  during 
the  second  half  of  diastole. 


Ringer  devised  a  special  solution  of  salts  for  the  maintenance 
of  the  heart-beat.  It  consists  of  sodium  chloride  solution,  0.7  per 
cent.;  Calcium  chloride,  0.00026  per  cent.;  solution  of  potassium 
chloride,  0.035  per  cent.  Oxygen  is  very  beneficial  when  added  to 
the  Einger  solution. 

Blood-corpuscles  are  not  necessary  for  the  contraction  of  the 
mammalian  heart.  Carbonic  acid  reduces  the  contractile  force  and 
rate  of  the  heart-beat. 

Locke  found  that,  by  adding  a  l-per-cent.  solution  of  dextrose 
to  Ringer's  fluid  provided  with  oxygen,  it  kept  the  mammalian  heart 
beating  for  hours.     Hering,  by  an  artificial  circulation,  restored  the 


246  PHYSIOLOGY. 

heart-beat  for  several  hours  in  a  man  who  had  been  dead  eleven 
hours.  Kubliabko,  by  Kinger's  solution,  restored  the  heart  in  ani- 
mals which  bad  been  dead  four  days.  In  a  dead  monkey,  Hering, 
with  artificial  circulation,  found  the  vagus  retained  its  inhibitory 
power  for  six  hours  after  death,  whilst  the  accelerator  was  active 
over  fifty-three  hours  after  death. 

Porter  has  found  that  the  mammalian  heart  beats  best  when 
supplied  withljlood  from  the  same  species  of  anmial.  Loeb  explains 
these  actions  of  salts  in  promoting  the  contractions  as  ionic  action. 
Thus,  the  ions  of  sodium  produce  contractions  of  the  heart,  whilst 
the  ions  of  calcium  and  potassium  inhibit  them.  H+  and  OH 
accelerate  the  action  of  the  sodium,  although  themselves  not  pro- 
ducing rhythmic  contractions.  Ions  act  either  on  the  physical  con- 
dition of  proteids  of  protoplasm,  or  accelerate  their  chemical  actions. 

THE  ARTERIES. 

All  vessels  leaving  the  heart  are  arteries.  From  it  proceed  the 
aorta  and  pulmonary  artery,  the  former  from  the  left,  the  latter 
from  the  right  ventricle.  All  of  the  branches  of  the  arteries  con- 
tinue to  divide  to  form  smaller  arteries,  these  in  turn  become 
arterioles,  which  are  followed  by  capillaries  (hairlike  vessels).  To 
cause  as  little  friction  as  possible  the  branches  are  almost  uniformly 
given  off  at  an  acute  angle;  the  total  area  of  the  cross-sections  of 
the  branches  is  usually  greater  than  the  sectional  area  of  the  orig- 
inal trunk  from  which  sprung  the  branches.  As  the  distance  from 
the  source  is  increased  the  area  supplied  by  the  branches  is  increased 
also,  giving  the  general  impression  of  a  cone  in  its  contour ;  its  base 
is  outlined  by  the  capillaries,  its  apex  being  represented  by  the  point 
from  which  the  branch  springs  from  the  parent  trunk. 

The  pulmonary  artery  arises  from  the  right  ventricle  in  front 
of  the  origin  of  the  aorta  under  whose  arch  it  very  shortly  passes, 
then  to  divide  into  two  main  branches,  one  for  each  lung.  Within 
the  lung-substance  they  divide  and  subdivide  very  rapidly  to  form 
numerous  capillaries,  in  order  that  the  blood  may  become  thoroughly 
oxidized. 

Because  of  the  considerable  amount  of  muscular  and  elastic 
fibers  present  in  the  walls  of  the  arteries,  they  (unlike  veins)  are 
usually  found  empty  and  dilated  after  death. 

Arterial  Structure. — The  walls  of  the  arteries  are  composed  of 
three   coats:    an    internal   one    of   endothelial   nature,   the   tunica 


THE  CIRCULATION.  247 

intima;  a  middle  coat  of  muscular  fibers,  tunica  media;  and  an 
external,  cellular  coat,  tunica  adventitia. 

Tunica  Intima. — The  tunica  intima  of  the  arteries  is  the  thin- 
nest coat  and  the  most  transparent  and  elastic.  These  properties 
permit  the  caliber  of  the  artery  to  be  enlarged  without  any  great 
danger  of  rupturing  its  walls.  It  is  composed  of  three  different 
structures:  (1)  an  epithelial  layer,  the  endothelium,  which  consists 
of  elliptical  cells;  (2)  a  subepithelial  layer,  which  is  composed  of 
connective  tissue  with  branched  cells;   (3)  an  elastic  layer. 

By  reason  of  its  smooth  surface  there  is  very  little  friction  in 
the  rush  of  the  blood-current. 

Tunica  Media. — It  is  composed  of  two  varieties  of  tissue:  (1) 
muscular  and  (2)  elastic. 

The  unstriped  muscular  fibers  run  in  a  circular  direction  around 
the  vessels.  In  the  large  arteries  there  is  a  predominance  of  elastic 
tissue;  in  the  arterioles  there  is  no  elastic,  but  muscular  tissue. 
The  contractility  of  the  arteries  depends  upon  the  muscular  tissue. 
Where  there  is  an  excess  of  elastic  tissue  there  is  very  little  muscular 
tissue  in  the  blood-vessel,  and  where  the  elastic  tissue  is  at  a  mini- 
mum there  is  a  maximum  of  muscular  tissue. 

Tunica  Adventitia. — This  coat  is  composed  of  bundles  of  con- 
nective tissue  with  some  elastic  tissue. 

Vasa  Vasorum. — Like  every  other  tissue,  the  wall  of  the  ves- 
sels needs  nutritive  supplies.  This  is  supplied  by  small  capillaries 
which  run  only  in  the  tunica  adventitia  of  the  blood-vessel.  To 
these  vessels  has  been  given  the  name  of  vasa  vasorum. 

VEINS. 

Like  the  arteries,  veins  are  branching  tubes;  but  they  are  larger, 
more  numerous,  and  as  a  consequence  have  more  capacity  to  hold 
blood.  Veins  have  their  beginnings  in  the  capillary  vessels,  which 
by  gradually  uniting  form  the  small  veins.  These  small  veins  unite 
to  form  larger  ones,  the  venae  cavffi,  which  empty  into  the  right 
auricle.  The  veins  have  about  three  times  the  capacity  of  the 
arteries.  The  veins  consist  of  a  superficial  and  a  deep  set,  the  former 
not  associated  with  the  arteries  and  being  subcutaneous,  the  deep 
set  usually  running  along  the  side  of  the  artery  and  hence  called 
venje  comites.  Anastomoses  between  the  veins  of  large  size  are 
more  frequent  than  in  the  corresponding  arteries.  The  veins,  like 
the  arteries,  have  an  external,  a  middle,  and  an  internal  coat.  The 
coats  of  the  veins  are  much  thinner  than  the  coats  of  the  arteries, 


248  PHYSIOLOGY. 

and  when  divided  the  veins  collapse,  while  the  arteries,  divided,  stand 
open.  The  walls  of  the  veins  are  inelastic,  because  they  have  no 
elastic  tissue. 

Valves. — The  chief  feature  of  the  veins  is  the  valves,  which  are 
so  arranged  as  to  prevent  the  blood  from  flowing  backward.  The 
valves  ordinarily  are  in  pairs  opposite  each  other  and  are  formed  of 
crescent-shaped  doublings  of  the  lining  membrane  of  the  veins,  with 
some  interposed  fibro-elastic  tissue.  The  valves  are  directed  toward 
the  heart.  If  a  vein  is  compressed  the  blood  is  driven  back  and 
presses  the  valves  inward  and  closes  the  vein.  The  pulmonary  veins 
contain  no  valves,  and  the  same  may  be  said  for  the  superior  and 
•  inferior  vena  cavEe,  the  portal  vein,  and  most  of  those  of  the  head 
and  neck.  The  veins  of  the  lower  extremities  contain  more  valves 
than  the  corresponding  vessels  of  the  upper  extremity.  In  certain 
organs  channels  are  seen  lined  with  an  extension  of  the  internal  coat 
of  the  vein,  which  are  called  venous  sinuses,  as  in  the  dura  mater 
and  uterus.  Vasa  vasorum  are  also  distributed  to  the  veins.  In  the 
coats  of  both  arteries  and  veins  are  lymph-spaces. 

The  nerve-supply  to  the  arteries  is  liberal,  to  the  veins  much 
less  so.  The  supply  is  derived  chiefly  from  the  sympathetic  system, 
with  a  few  filaments  from  the  cerebro-spinal  system.  Upon  the 
larger  vessels  these  nerves  form  plexuses  with  ganglia  at  frequent 
intervals. 

THE  CAPILLARIES. 

The  smallest  arteries  suddenly  divide  into  an  extremely  fine  net- 
work of  hairlike  tubes,  the  capillaries.  These  furnish  the  connect- 
ing link  between  arteries  and  the  beginnings  of  veins.  They  serve 
as  the  intermediate  agent  in  all  structures,  between  the  arteries  and 
the  veins. 

Each  capillary  tube  is  from  ^/oooo  to  Vsooo  i^^ch  in  diameter, 
while  it  averages  V30  inch  in  length. 

Capillaries  are  composed  of  the  same  kind  of  endothelial  cells 
that  the  intima  of  the  arteries  is;  in  fact,  the  capillaries  seem  to 
be  the  prolongations  of  the  lining  of  the  arteries.  Their  walls  are 
made  up  of  a  single  layer  of  lance-shaped  endothelial  cells.  In  the 
wall  of  the  capillary  between  the  cells  we  find  the  cement-substance 
which  permits  the  blood-corpuscles  to  penetrate  it  in  diapadesis. 
These  little  vessels  penetrate  the  spaces  between  the  cells  of  the 
tissues  in  such  a  fine  network  that  many  of  the  cells  are  in  contact 
with  several  vessels.     So  closely  arranged  are  they  that  the  point  of 


THE  CIRCULATION.  249 

a  very  fine  needle  cannot  enter  the  skin  witliout  injuring  some  of 
them. 

The  total  capacity  of  the  capillaries  is  about  three  hundred 
times  that  of  the  arteries,  so  that  in  them  much  of  the  blood-pres- 
sure is  lost,  but  normally  there  always  remains  sufficient  to  main- 
tain a  steady  movement. 

THE   CIRCULATION   OF   THE   BLOOD. 

The  physicians  and  naturalists  of  antiquity,  even  at  the  epoch 
when  they  were  permitted  to  get  enlightenment  from  anatomy, 
remained  in  ignorance  of  the  circulatory  movement  of  the  blood. 
The  circulatory  apparatus  is  not  one  of  those  the  mere  inspection 
of  which  could  reveal  its  function ;  in  fact,  when  viewed  in  a  cadaver 
illusions  are  very  apt  to  rise.  In  it  the  arteries  are  empty  and  show 
a  gaping  cavity  when  incised,  so  that  they  were  thought  to  contain 
air  or  some  subtle  spirit,  the  latter  taking  its  origin  in  the  ventricles 
of  the  brain  to  reach,  in  some  unaccountable  manner,  the  circula- 
tory system.  To  them  the  name  artery  was  given,  since  the  veins 
alone  were  believed  to  be  the  true  blood-vessels.  Such  was  the 
opinion  entertained  by  men  who  lived  in  the  fourth  and  fifth  cen- 
turies before  the  Christian  era. 

In  the  second  century  of  our  era  Galen  discovered,  by  means  of 
vivisections,  that  the  arteries  contain  blood.  He  even  admitted  that 
the  arteries  communicated  with  the  veins.  But,  as  if  to  pay  his  debt 
to  error,  he  professed  that  the  two  hearts  are  in  communication  with 
one  another  through  numerous  apertures  which  riddle  the  septum 
that  separates  the  two.  For  nearly  fourteen  centuries  the  opinions 
of  Galen  had  inviolate  authority,  when  it  was  finally  ascertained  by 
Vesalius  that  the  separating  septum  was  not  perforated.  It  was 
Michael  Servetus  who,  in  a  theological  work,  clearly  pointed  out  the 
passage  of  the  blood  from  the  right  heart  to  the  left  through  the 
pulmonary  hlood-vessels.  His  system  was  true,  but  not  based  upon 
experiment,  since  he  knew  nothing  of  the  heart's  force  and  valves. 

It  was  in  1G28  that  William  Harvey  published  his  immortal  dis- 
covery of  the  circulation  of  the  blood.  True,  a  great  deal  had  been 
suspected  and  there  abounded  a  perfect  chaos  of  confused  and  scat- 
tered facts.  He  established  by  numerous  and  admirably  interpreted 
experiments  his  doctrine  of  the  two  circulations:    great  and  small 

To-day  it  would  be  superfluous  to  recall  all  of  the  argimients 
which  Harvey  had  to  make  use  of  to  prop  up  that  doctrine.  There- 
fore there  will  be  stated  here  only  some  of  his  experimental  proofs, 


250  PHYSIOLOGY. 

the  interpretation  of  which  appears  easy  to  us  in  the  liglit  of  our 
present  knowledge. 

When  an  artery  is  opened,  said  Harvey,  the  blood  issues  in 
unequal  jerks,  alternately  weaker  and  stronger.  The  stronger  coin- 
cides with  diastole  of  the  artery  and  consequently  with  ventricuhir 
systole.  Also,  if  an  artery  of  a  living  animal  be  cut  across,  the  blood 
continues  to  gush  by  jerks  from  that  end  of  the  vessel  still  in  com- 
munication with  the  heart,  whereas  it  soon  ceases  to  flow  from  that 
severed  end  which  is  more  remote  from  the  central  organ. 

When  the  arm  is  bound,  as  for  bleeding,  the  veins  swell  up 
below  the  ligature  to  become  knotty  on  a  level  with  their  valves.  If 
force  be  attempted  to  press  the  blood  away  from  the  heart,  the 
knots  become  more  marked;  on  the  contrary,  if  the  blood  be  pressed 
toward  the  heart,  it  passes  freely.  From  this  Harvey  deduced  that 
the  direction  of  the  venous  blood  is  from  the  periphery  to  the  heart. 

When  an  artery  is  obstructed,  the  blood  accumulates  between 
the  heart  and  the  obstacle ;  on  the  contrary,  the  accumulation  in  the 
case  of  a  vein  is  between  the  obstructed  point  and  the  general  capil- 
laries. In  the  arteries,  therefore,  the  blood  flows  from  the  heart  to 
the  extremities;  in  the  veins,  from  the  extremities  toward  the  heart. 

If  an  artery  be  completely  severed  and  the  animal's  blood  be 
permitted  to  flow,  all  of  its  blood  will  eventually  pass  through  the 
opening.  Would  this  occur  if  there  were  not  a  continual  passage 
of  the  blood  from  the  heart  to  the  arteries,  then  to  the  veins,  and 
finally  to  the  heart  again;   that  is  to  say,  a  true  circulation? 

This  great  physiologist  also  observed  that  if  poison  be  injected 
at  but  a  single  point  there  will  follow  a  general  constitutional  dis- 
turbance, explained  only  by  the  movement  of  this  vital  fluid  through- 
out tlie  entire  body. 

To  be  able  to  ascertain  by  vision  the  direct  passage  of  the  blood 
from  the  arteries  into  the  veins  was  not  allowed  Harvey.  It  was 
left  to  Malpighi,  who,  in  IGGl,  while  examining  the  lung  and  mesen- 
tery of  a  frog  with  the  aid  of  a  microscope,  was  able  to  note  the 
circulation  of  the  blood  in  the  capillary  blood-vessels.  The  spec- 
tacle of  capillary  circulation  within  the  web  of  a  frog's  foot  or  tail 
of  a  tadpole  is  within  the  reach  of  every  student.  Harvey  was 
denied  this  from  lack  of  lenses  powerful  enough  to  demonstrate  it. 

Now  that  the  general  plan  of  the  circulation  has  been  noted, 
attention  is  naturally  turned  toward  the  principles  governing  the 
flow  of  the  blood.  The  mechanical  act  of  impulsion  can  be  readily 
imitated  by  physical  apparatus,  but  physics  do  not  account  for  a  cer- 


THE  CIRCULATION. 


251 


tain  part  of  the  body  receiv- 
ing blood,  now  more,  now  less, 
abundantly;  become  congested 
or  pale,  warm  or  cold;  and  at 
the  same  time  the  impetus  re- 
maining perceptibly  the  same. 
By  employing  a  simple 
piece  of  apparatus,  designed  by 
E.  H.  A\'eber,  the  main,  simple, 
physical  phenomena  of  the  cir- 
culation may  be  simulated.  To 
imitate  the  Harveian  circuit, 
take  a  piece  of  small  intestine, 
sufficiently  long,  and  join  the 
two  ends  so  that  there  is  formed 
a  closed  and  circular  conduit. 
A  part  of  this  elastic  conduit  is 
limited  by  two  valves  which 
open  according  to  the  direction 
it  is  desired  that  the  current  of 
liquid  should  go.  The  arrange- 
ment of  the  valves  is  such  that 
all  backward  flow  is  prevented. 
On  filling  the  apparatus  with 
water  by  means  of  a  funnel,  it  is 
ready  for  operation.  When  any 
portion  of  this  elastic  conduit  is 
squeezed  the  liquid  immediately 
beneath  the  point  of  pressure 
attempts  to  escape.  This  it  can 
do  only  in  one  direction  (because 
of  the  valves),  thereby  produc- 
ing a  forward  motion  of  the 
liquid.  With  each  compression 
there  follows  a  corresponding 
wave,  so  that  if  the  compres- 
sions be  numerous  enough  the 
liquid  will  move  round  and 
round  within  the  conduit.  This 
represents  only  very  imperfectly 
the  circulation  of  the  blood;  in 


Fig.  90. — Weber's  Schema. 

4-5  and  8-9  are  two  pieces  of  intestine  of 
the  same  size.  6,  A  piece  of  glass  tubing.  11 
and  2,  Two  wooden  tubes.  1,  A  short  piece  of 
intestine.  3,  12,  Valves  which  open  only  in  one 
direction.  1  represents  the  ventricle.  10,  A 
funnel  to  let  water  enter  the  schema.  4-5,  The 
arterial  system.  8-9,  The  venous  system.  7, 
A  sponge  representing  the  capillaries.  3,  The 
semilunar  valve.  12,  The  auriculo-ventricular 
valve. 


252  PHYSIOLOGY. 

the  living  apparatus  the  impulse  of  the  heart  is  not  at  the  end  of 
the  venous  system. 

From  the  operation  of  even  so  simple  a  piece  of  apparatus,  it 
cannot  but  be  noticed  that  tlic  circulation  depends  upon  a  difference 
of  tension.  Liquids  always  take  the  direction  of  the  pressure.  The 
obstruction  offered  to  the  blood  in  the  presence  of  the  capillaries 
has  a  tendency  to  increase  arterial  tension  at  the  expense  of  venous 
pressure.  The  narrower  and  more  difficult  the  capillaries  to  be  tra- 
versed are,  the  greater  is  arterial  pressure,  or  vice  versa.  The  prime 
cause  of  difference  of  pressure  is  ventricular  contraction,  aided,  how- 
ever, by  elasticity  of  vessels, 

CIRCULATION   IN  THE  BLOOD=VESSELS. 

This  field  of  physiology  presents  problems  of  a  physical  nature, 
in  that  the  flow  of  the  liquid,  blood,  is  through  tubes.  But  it  must 
])e  remembered  that  the  tubes  employed  in  the  circulation  are  living, 
more  or  less  elastic  ones,  and  that  physical  laws  are  correspondingly 
altered. 

The  analogy  between  the  nervous  system  and  the  telegraphic 
system  is  a  very  striking  one,  and  is  much  used  by  physiologists  and 
others.  Even  more  forceful  is  the  analogy  between  the  circulatory 
system  and  the  system  of  water-supply  of  a  town  or  city,  except  that 
there  is  no  return  of  the  latter's  fluid  to  the  starting-place.  The 
water  starts  upon  its  flow  from  the  elevated  reservoir  to  pass  through 
large  mains  at  first  and  is  distributed  through  branches  that  become 
smaller  and  smaller  as  they  subdivide  on  their  way  to  different 
houses.  Likewise,  the  blood  starts  from  the  centrally  located,  pump- 
ing heart,  passes  through  large  trunks  at  first,  to  be  distributed 
through  branches  that  become  smaller  and  smaller  as  they  subdivide 
on  their  way  to  different  tissues.  In  short,  the  physical  laws  of  the 
circulation  are  the  modified  physical  laws  of  the  flow  of  liquids 
through  tubes.  From  this  it  will  be  readily  deduced  that  a  com- 
petent knowledge  of  the  laws  of  circulation  must  be  preceded  by 
some  knowledge  of  physical  laws.  These  will  be  referred  to  from 
time  to  time  in  the  treatment  of  the  present  subject. 

The  flow  of  liquid  is  caused  by  a  difference  of  pressure  between 
the  different  parts  of  a  body  of  liquid.  The  attraction  of  the  earth 
(gravitation)  provides  a  continuous  pressure  which  will  produce  a 
flow  of  liquid  along  channels  or  through  tubes,  provided  the  source 
be  elevated  and  the  outlet  low. 

The  circulation  through  the  heart-vessels  is  also  caused  by  a 


THE  CIRCULATION.  253 

difference  in  pressure  due  to  the  primary  propelling  force  of  the 
heart-action.  That  is,  the  pressure  in  it  exceeds  that  of  the  arteries; 
the  latters  pressure,  kept  high  by  the  heart's  force  and  peripheral 
resistance,  is  greater  than  that  in  the  capillaries.  Though  that 
exerted  in  the  capillaries  is  small,  it  is  yet  in  excess  of  that  existing 
in  the  veins.  The  lowest  pressure  is  found  in  the  blood  about  to 
enter  the  heart  after  having  first  made  its  circuit  through  the  body- 
tissues.  The  direction  of  the  flow  of  any  liquid  is  always  from  the 
higher  pressure  toward  the  lower;  therefore  the  flow  of  blood  within 
the  body  is  from  the  heart  around  through  the  body  back  to  the  heart 
again;   that  is,  it  circulates. 

ELASTICITY  OF  THE  ARTERIES. 

It  is  known  that  the  blood  is  sent  out  by  the  heart  in  an  inter- 
mittent manner,  each  contraction  of  the  ventricle  pushing  a  mass, 
as  the  stroke  of  the  piston  of  a  force-pump  would  do.  If,  however, 
the  movement  of  the  blood  in  the  capillaries  is  observed  with  a  micro- 
scope it  is  ascertained  that  in  the  normal  state  it  is  perfectly  con- 
tinuous. The  movement  of  blood  has  been  transformed  in  its  course 
from  the  heart  to  the  extremities.  This  transformation  of  the  move- 
ment is  due  to  the  elasticity  of  the  arteries.  Hydraulics  has  ascer- 
tained this  remarkable  effect  of  elasticity  in  fire  engines,  for  example ; 
the  water  from  the  machine  is  rendered  less  jerky  by  running  liquid 
under  a  bell  filled  with  air;  the  elastic  force  of  the  gas  thus  com- 
pressed transforms  the  brief  and  intermittent  impulsion  of  the 
stroke  to  a  continuous  stream. 

Intermittent  Afflux  Apparatus. — Marey  has  experimentally  dem- 
onstrated that,  in  the  case  of  intermittent  afflux  of  liquid  in  a  con- 
duit of  a  given  caliber,  the  elasticity  of  that  conduit  increases  the 
quantity  of  the  liquid  that  can  penetrate  there  under  a  given  pres- 
sure. 

Suppose  a  force-pump,  from  which  runs  a  tube  furnished  with 
a  stop-cock;  a  tube  which  bifurcates  at  a  point  to  be  continued  by 
two  conduits  of  the  same  caliber.  One  of  these  is  made  with  elastic; 
walls  (C ),  the  other  with  rigid  walls  (B).  A  valve  placed  in  the 
elastic  tube  prevents  the  liquid  from  flowing  back  from  the  tube, 
hut  offers  no  obstacle  to  its  direct  current.  Two  lips  of  the  same 
caliber  are  fitted  to  the  ends  of  the  two  tubes. 

When  the  stop-cock  is  opened  and  the  outflow  is  permitted  to  es- 
tablish itself  in  a  continuous  manner,  both  the  rigid  and  elastic  tubes 
pour  out  the  same  quantity  of  liquid.     If,  on  the  contrary,  the  stop- 


254 


PHYSIOLOGY. 


cock  be  opened  and  shut  alternately  so  as  to  produce  an  intermittent 
access  of  the  liquid,  the  outtlow  is  greater  through  the  elastic  tube 
than  through  the  rigid  tube. 

The  blood-circulation  being  of  the  intermittent  afflux  order,  the 
arterial  elasticity  is  favorable  to  the  entrance  of  the  blood  thrown  off 
by  the  heart.  By  the  elasticity  of  the  vessel  there  is  produced  a 
diminution  of  the  resistance  the  liquid  meets  with.  The  so-called 
"friction"  will  be  much  slighter;  so  that  the  heart  will  be  able  to  send 
out  from  its  ventricles  a  greater  quantity  of  blood  with  much  less 
expenditure  of  force. 

The  circulation  in  the  arteries  is  under  the  dependence  of  two 
very  important  properties  of  these  vessels :  elasticity  and  contrac- 
tility. The  nature  of  the  movement  of  the  blood,  has,  therefore,  been 
transformed  in  its  course  from  the  heart  to  the  extremities.     It  is 


Fig.  91. — Marey's  Intermittent  AfHux  Apparatus.     (Lahousse.) 
A,  Force-pump.    B,  Tube  with  rigid  waUs.     C,  Tube  with  elastic  waUs. 

now  known  that  this  transformation  is  due  in  the  main  to  the  elas- 
ticity of  the  arteries. 

Each  new  entrance  of  the  blood  into  the  arterial  system  must 
necessarily  be  accompanied  Avith  a  dilatation  of  the  whole  vascular 
tree.  As  soon  as  the  three  ounces  of  blood  which  has  been  ejected 
from  the  left  ventricle  has  penetrated  into  the  aorta,  as  it  flows 
through  the  capillary  system  there  results  a  contraction  of  the  whole 
arterial  system  until  the  moment  when  a  new  output  of  blood  arrives. 

It  has  been  ascertained  experimentally  that  the  arterial  vessels 
are  much  more  elastic  in  the  direction  of  their  axis  than  in  their 
transverse  diameter.  It  is  in  the  former  direction,  then,  that  increased 
capacity  of  the  arteries  will  especially  occur.  When  the  trunks  of 
the  arteries  are  of  considerable  extent  the  elongation  may  become 


THE  CIRCULATION.  255 

apparent  to  the  naked  eye,  as  in  the  temporal  artery,  while  there  will 
not  seem  to  exist  any  increase  in  the  transverse  direction  of  the  same 
vessel. 

According  to  Weber,  the  principal  role  of  arterial  elasticity  is  to 
establish,  between  the  arterial  and  venous  tensions,  a  difference  which 
is  indispensable  to  the  movement  of  the  liquid  within  the  circulatory 
apparatus.  In  addition,  the  uses  of  vascular  elasticity  may  be  said  to 
be  twofold:  On  the  one  hand,  it  saves  the  heart  a  considerable  dis- 
play of  force;  on  the  other,  it  furnishes  the  small  vessels  with  a  con- 
tinuous and  constant  flow  of  blood. 

Next  in  importance  to  the  elasticity  of  the  vessels  is  the  power  of 
contractility,  by  which  the  caliber  of  a  vessel  is  changed  and  the  sup- 
ply of  blood  to  any  part  or  organ  of  the  body  altered.  This  property 
co-operates  with  elasticity,  so  that  the  lumen  of  any  given  vessel  is 
proportionate  to  the  pressure  exerted.  Were  it  otherwise,  at  some 
times  the  pressure  would  be  too  small,  at  other  times  too  great,  for 
the  quantity  of  inclosed  blood.  The  power  of  contractility  is  very 
prominent  in  the  small  arteries. 

THE  PULSE. 

At  each  ventricular  systole  the  ventricular  contents  are  forced 
into  the  arterial  system,  but,  because  of  the  high  peripheral  tension, 
they  are  unable  to  pass  along  as  a  unit.  In  fact,  the  artery  just 
beyond  the  heart  becomes  distended  because  of  this  influx,  but  by 
virtue  of  its  elasticity  it  strives  to  regain  its  normal  caliber,  thereby 
giving  to  the  blood  some  motion.  The  main  impetus  of  the  blood  is 
given  by  the  succeeding  systoles,  until  the  smaller  arteries  are  reached, 
when  the  vascular  elasticity  asserts  itself  more,  and  so  helps  along  the 
blood-stream.  By  this  means  the  blood  is  caused  to  circulate.  If  the 
vessels  were  inelastic,  just  as  much  blood  would  be  forced  out  of  the 
veins  into  the  heart  again  as  the  heart  at  each  beat  injects  into  the 
arteries.  Though  the  blood  in  the  elastic  vessels  of  the  body  cannot 
move  freely  as  in  the  inelastic  tubes,  yet  there  is  propagated  at  each 
ventricular  systole  a  irave  which  runs  to  the  periphery  of  the  body. 
This  wave  is  not  an  actual  movement  of  the  particles  of  the  blood,  but 
a  transmission  of  the  impulsion  of  the  heart  throughout  the  length  of 
the  arterial  tree.  To  this  wave  has  been  given  the  name  pulse.  This 
impulsion  moves  very  swiftly  without  the  liquid  itself  participating 
in  that  swiftness.  This  wave  travels  28V2  feet  per  second.  When  a 
systole  of  the  heart  is  revealed  by  a  beating  of  the  radial  artery,  there 
is  not,  at  that  moment,  under  one's  finger  a  single  drop  of  the  blood 


256  PHYSIOLOGY. 

thrown  off  l)y  the  hist  systole.  There  is  only  the  movement  of  that 
blood  which  is  transmitted  hy  the  continuity  of  the  liquid.  Tlie 
pulse  may  be  compared  to  a  wave  produced  by  throwing  a  stone  into 
the  pond. 

The  three  factors  concerned  in  the  production  of  the  pulse  are : 
(1)  the  action  of  the  heart,  (2)  the  elasticity  of  the  large  vessels,  and 
(o)  the  resistance  of  the  smaller  arteries  and  the  capillaries. 

The  pulse  is  really  a  shock,  perceptible  to  the  touch  at  each  in- 
crease of  the  arterial  tension,  and  produced  by  successive  affluxes  of 
the  blood  which  the  heart  throws  off. 

In  order  to  perceive  that  shock,  the  vessel  must  be  pressed  by  the 
finger  so  as  to  make  it  lose  its  cylindrical  form  at  that  point.  By 
reason  of  the  dilatation  of  the  vessel,  the  finger  is  raised  at  that  point. 
That  is,  one  perceives  the  pulse.  As  there  may  exist  various  changes 
in  the  arterial  tension,  so  there  may  be  various  types  of  pulse.  Vari- 
ations are,  for  the  most  part,  pathological,  and  so  may  be  considered 
to  be  outside  of  the  domain  of  physiology. 

When  the  physician  feels  the  patient's  pulse  he  gains  valuable 
information  as  to  the  condition  of  the  heart  and  vessels.  The  exam- 
ination of  the  characters  of  the  pulse  is  usually  confined  to  that  por- 
tion of  the  radial  artery  which  lies  in  the  wrist.  Here  the  artery  is 
covered  only  by  skin  and  subcutaneous  tissue,  while  in  addition  the 
shaft  of  the  radius  forms  a  bony  support  against  which  the  artery  may 
be  compressed  by  the  fingers.  From  the  pulse  are  noted  the  following 
points:    Force,  rate,  and  fullness. 

While  such  main  features  of  the  pulse  were  able  to  be  depicted 
by  experienced  finger-tips,  it  was  felt  that  there  was  still  very  much 
that  the  pulse  would  tell  could  it  but  be  translated. 

Everyone  has  seen  the  movements  produced  in  a  limb  by  reason 
of  the  pulsations  of  the  popliteal  artery,  when  one  leg  is  kept  crossed 
over  the  knee  of  the  other.  The  leg  in  this  position  represents 
typically  a  lever  of  the  third  class. 

One  observer  conceived  the  idea  from  this  phenomenon  that  the 
pulse  can  be  very  accurately  studied  by  using  a  very  light  lever  so 
attached  that  it  will  oscillate  at  each  heart-beat.  By  virtue  of  a  large 
arm  to  the  lever  the  amplitude  of  the  oscillations  is  so  exaggerated 
that  they  can  be  readily  seen  by  the  naked  eye  and  their  movements 
graphically  depicted  upon  smoked  papers.  The  instrument  capable 
of  determining  the  various  elements  of  the  pulse  and  so  depicting 
them  that  they  can  be  studied  at  leisure  has  received  the  name 
sphygmograph. 


THE  CIRCULATION.  257 

The  Sphygmograph.. — The  name  whereby  this  instrument  is 
known  is  derived  from  two  Greek  words  which  mean  "to  write  the 
pulse."  It  does  write,  for  to-day  graphic  records  of  the  various  fea- 
tures of  the  pulse  are  obtained  by  its  use. 

The  essential  feature  of  this  instrument  is  its  system  of  com- 
pound levers  whereby  the  initial  motion  is  multiplied  about  fifty 
times.  The  foot  of  these  levers  rests  upon  the  skin  over  the  artery 
whose  tracing  is  to  be  taken.  Motion  is  transmitted  from  it  to  the 
other  end  of  the  levers,  where  is  inserted  a  recording  needle. 

The  second  feature  of  the  apparatus  is  the  recording  instrument, 
composed  of  clock-work,  which  revolves  a  pair  of  small  cylinders 
between  which  is  moved  a  ribbon  of  blackened  paper.  The  record- 
ing-needle's point  rests  upon  this  paper,  correctly  depicting  there  the 
various  features  of  the  pulse. 


Fig.  92. — Marey's  Sphygmograph.     (Yeo.) 

The  parts  B,  B,  B  are  fastened  to  the  wrist  by  the  straps  B,  B.  The 
remaining  part  of  the  instrument  rests  on  the  forearm.  The  end  of  the  screw, 
y,  rests  on  the  spring  R,  the  button  of  which  lies  on  the  radial  artery.  Any 
movement  of  the  button  at  R  is  communicated  to  V,  which  moves  the  lever, 
L,  up  and  down.  When  in  position,  the  blackened  slip  of  glass  is  made  to 
move  evenly  by  the  clockwork,  U,  so  that  it  records  the  movements  of  the 
lever. 

In  addition,  each  instrument  is  provided  with  an  apparatus  by 
adjustment  of  which  the  pressure  is  so  regulated  that  the  best  record 
may  be  obtained.  The  graphic  record,  or  pulse-tracing,  is  known  as 
the  spliygmogram. 

The  main  features  of  the  sphygmographic  record  are  an  abrupt 
ascent  with  a  descent  that  is  more  gradual  and  wavy,  representing  the 
rise  and  fall  in  pressure  due  to  ventricular  systole  and  diastole.  The 
wavy  appearance  of  the  downstroke  is  due  to  the  elastic  recoil  being 
more  constant  and  of  longer  duration  than  the  ventricular  systole. 
The  sudden  upstroke  represents  very  forcibly  the  sudden  influx  of 
blood  into  the  aorta  during  systole,  while  the  more  gradual  down- 
stroke  represents  the  slower  fall  of  arterial  pressure  during  diastole. 

17 


258 


PHYSIOLOGY. 


The  line  of  ascent  represents  the  dihvtation  of  the  artery  by  ven- 
tricular systole  when  the  semilunar  valves  are  forced  open  and  the 
contents  are  projected  into  the  artery.  The  top  of  the  primary  wave 
is  pointed  normally;  so  has  received  the  term  apex. 

The  more  gradual  downstroke  is  interrupted  by  two  completely 
distinct  elevations  of  secondary  waves,  though  in  the  lowest  part  of 
the  descent  there  may  be  several  minor  inequalities.  The  more  dis- 
Gnct  of  the  two  occurs  at  about  the  middle  portion  of  the  line  of 
descent.  It  represents  the  dicrotic  wave;  from  its  mode  of  origin  it 
is  sometimes  called  the  "recoil  wave."     Between  the  apex  and  the 


Fig.  93. — Dudgeon's  Sphygmograph.      (Lahousse.) 

dicrotic  wave  occurs  the  predicrotic,  or  tidal  wave,  wliile  below  the 
dicrotic  wave  occurs  the  postdicrotic  wave  or  waves,  since  there  are 
very  frequently  several. 

The  line  of  ascent  and  the  predicrotic  wave  are  caused  l)y  systole, 
while  the  dicrotic  wave  takes  place  during  diastole.  The  postdicrotic 
waves  are  a  result  of  vascular  tension. 

Origin  of  the  Dicrotic  Wave. — At  one  time  this  wave  was  be- 
lieved to  have  its  origin  in  the  periphery,  but  is  now  known  to  be 
caused  as  follows:  By  ventricular  systole  there  is  projected  into  the 
full  aorta  a  mass  of  blood  so  that  a  positive  wave  is  propagated  from 
the  heart  toward  the  periphery,  where  it  becomes  extinguished 
among  the  smallest  arterioles  and  capillaries.     At  the  closure  of  the 


THE  CIRCULATION".  259 

semilunar  valves,  the  arteries,  from  having  just  been  distended,  begin 
to  contract  or  recoil  upon  the  contained  blood,  with  the  result  that 
this  newly  exerted  pressure  sets  it  into  motion  in  two  directions : 
toward  the  heart  and  toward  the  periphery.  In  the  latter  direction 
the  passage  is  free  until  the  capillaries  are  reached ;  toward  the  heart 
the  still  closed  semilunar  valves  are  met  with  such  force  that  there 
results  a  recoil.  This  develops  into  a  new  positive  wave,  which  gives 
the  dicrotic  wave  in  the  sphygmogram.  Atheroma  diminishes  the 
dicrotic  wave,  because  the  arterial  wall  is  more  rigid. 


Fig.   94. — Sphygmogram   Magnified.      (Laiiousse.  ) 

A,  B,  Corresponds  to  the  dilatation.  B,  D,  A,  Corresponds  to  contraction  of 
artery.  A,  C,  O,  A,  Measures  the  total  duration  of  pulse.  B,  C,  Repre- 
sents the   height  of  the  pulse.      D,   Is  the  dicrotic   pulse. 

THE  CAPILLARY  CIRCULATION. 

From  anatomy  it  was  learned  that,  with  but  very  few  exceptions, 
blood  passes  into  a  network  of  very  thin-walled  and  hairlike  vessels, 
the  capillaries;  this  network  communicates  with  the  finest  radicles 
of  the  veins,  so  that  it  forms  a  connecting-link  between  the  veins  and 
arteries.  ^Anatomically,  the  capillaries  are  distinguished  from  the 
arterioles  by  the  absence  of  circularly  arranged  muscular  fibers  which 
the  arterioles  possess  and  by  whose  contraction,  under  vasomotor  influ- 
ence, their  lumina  are  diminished.  However,  the  caliber  of  the  capil- 
laries is  subject  to  change  also  by  reason  of  passive  blood-pressure 
exerted  upon  their  endothelial  cells.  The  real  cause  of  the  blood- 
pressure  in  the  capillaries  is  ventricular  systole;  but  this  is  modified 
by  the  caliber  of  the  arterioles. 

It  is  in  the  interior  of  these  hairlike  vessels  that  fluid  enters  into 
contact  with  organic  tissues  for  their  nourishment  and  growth.  The 
tissues  in  turn  unload  themselves  of  those  effete  and  deleterious  mat- 
ters which  represent  the  products  of  catabolic  processes. 

From  these  reciprocal  actions  between  the  tissues  and  the  blood 


260 


PHYSIOLOGY. 


there  result  in  the  latter  profound  modifications  after  it  has  passed 
the  capillary  system.  The  blood  now  presents  the  destructive  char- 
acters of  venous  blood. 

Placed  between  the  last  ramifications  of  the  arteries  and  the  first 
radicles  of  the  veins,  the  capillary  system  is  blended  with  these  two 


Fig.  95. — Frog's  Web,  Highly  Magnified.     (Yeo,  after  Huxley.) 

A,  WaH  of  capillary.  B,  Tissue  lying  between  the  capillaries.  C,  Epithe- 
lial cells  of  the  skin.  D,  Nuclei  of  epithelial  cells.  E,  Pigment-cells,  con- 
tracted. F,  Red  blood-corpuscles.  O,  H,  Red  corpuscles  squeezing  their  way 
through  a  narrow  capillary,  showing  their  elasticity.      /,  Whits  corpuscles. 


orders  of  vessels  without  the  intervention  of  any  transitional  medium. 
The  limits  assigned  to  this  system  by  anatomy  are  purely  fictitious. 
Physiology  would  be  greatly  embarrassed  if  it  had  to  determine  the 


THE  CIRCULATION.  261 

precise  point  where  the  vessels  are  no  longer  only  organs  of  transport 
for  the  hlood,  but  permit  an  exchange,  between  the  blood  and  tissues 
through  their  walls.  The  anatomist  places  the  length  of  the  capillary 
at  one-thirtieth  of  an  inch. 

As  previously  stated,  the  capillary  wall  is  formed  entirely  of  a 
simple  layer  of  endothelial  cells.  They  are  flat,  lance-shaped  cells 
Joined  edge  to  edge  and  represent  the  continuation  of  the  intima  of 
the  arteries.  The  outlines  of  the  cells  with  their  lines  of  junction  may 
be  beautifully  demonstrated  by  nitrate  of  silver  staining.  In  the 
capillaries  stained  by  silver  there  is  here  and  there  to  be  seen  between 
the  cells  an  increase  in  the  amount  of  the  intercellular  substance.  The 
white  blood-corpuscles  when  migrating  from  the  blood-vessels  pass 
between  the  endothelial  ceils. 

Microscopical  Examination. — When  a  thin  and  vascular  mem- 
brane belonging  to  a  Jiving  animal  is  placed  in  the  field  of  the  micro- 
scope, the  admirable  spectacle  observed  for  the  first  time  in  1661,  by 
Malpighi,  is  seen:  the  blood  is  circulating  in  the  capillary  vessels. 
For  this  examination,  frogs  present  several  parts  which  are  suitable: 
the  interdigital  membrane,  mesentery,  tongue,  bladder,  and  lungs. 

Differences  in  volume  of  the  capillaries  have  much  influence 
upon  the  movement  of  the  blood  in  their  interior.  In  the  widest 
capillaries  a  rapid  current  takes  place,  and  the  corpuscles  are  carried 
along  with  a  velocity  which  does  not  permit  distinguishing  their 
form  clearly.  In  the  smallest  vessels,  on  the  contrary,  the  corpus- 
cles progress  slowly.  In  fact,  the  slowness  of  the  current  and  dis- 
appearance of  the  pulse  are  the  chief  characteristics  of  the  capillary 
current.  For,  normally,  the  flow  through  the  capillaries  is  in  a 
steady,  constant  stream. 

In  the  very  smallest  vessels  the  corpuscles  are  often  at  some 
little  distance  from  one  another.  They  seem  to  advance  with  diffi- 
culty and  to  rub  against  the  walls  of  the  vessels.  According  to 
many  observers,  the  corpuscles  are  sometimes  obliged  to  bend  out 
of  shape  in  order  to  traverse  these  narrow  channels. 

At  other  times,  in  the  midst  of  the  intricacy  of  the  vessels  and 
of  the  various  directions  of  their  current,  two  capillaries  are  seen  to 
join  a  third.  Corpuscles  coming  along  the  two  vessels  alternately 
pass  into  the  single  capillary,  which  receives  them  one  by  one,  and 
through  which  they  pass  in  single  file.  Elsewhere  may  be  seen  a 
pile  of  corpuscles,  distinct  from  each  other,  and  all  of  which  pro- 
gress with  the  same  swiftness.  All  hasten  and  slacken  their  pace  at 
the  same  time.     At  other  points  a  complete  immobility  is  seen  in 


262  PHYSIOLOGY. 

consequence  of  some  temporary  obstruction  or  of  the  contrary  direc- 
tion of  the  current;  then  all  at  once  the  corpuscles  start  off  again. 

Except  in  the  very  smallest  capillaries,  it  is  noticed  that  the  red 
corpuscles  always  move  in  the  axis  of  the  current,  while  on  either 
side  of  this  thread  of  moving  cells  there  is  noticed  a  transparent 
layer  of  liquor  sanguinis  which  is  almost  perfectly  still  or  possesses 
only  slight  motion.  This  layer,  "Poiseuille's  still  space,"  where  it 
is  plainly  discernible,  occupies  about  one-fifth  of  the  space  on  each 
side  of  the  axial  current,  which  occupies  the  remaining  three-fifths 
of  the  lumen  of  the  vessel. 

"Within  the  smaller  blood-vessels  the  red  corpuscles  occupy  the 
middle  of  the  stream,  where,  in  single  file,  they  glide  along  with 
comparative  rapidity;  in  larger  vessels  two  or  three  may  fiow  along 
abreast.  Along  the  outer  edge  of  the  central  thread  of  red  blood- 
corpuscles  move  the  white  ones,  many  even  getting  into  the  space 
of  Poiseuille.  The  motion  of  the  white  corpuscles  is  one  of  rolling, 
particularly  when  they  are  in  the  clear  space  next  the  vessel-wall  or 
in  direct  contact  with  the  latter,  since  they  are  sticky  by  nature. 
The  contact  of  the  rapidly  moving  axis  current  also  assists  in  giv- 
ing to  the  white  corpuscles  their  rolling  motion.  Their  motion  is 
so  slow  at  times  that  they  adhere  to  the  vessel-wall. 

It  has  been  demonstrated  by  physical  experiments  that  particles 
of  least  specific  gravity  (white  corpuscles)  in  all  capillaries  are 
pressed  toward  the  wall,  while  those  of  greater  specific  gravity  (red 
corpuscles)  remain  in  the  middle  of  the  stream. 

One  of  the  characteristics  of  the  capillary  circulation  is  the  dis- 
appearance of  the  pulse.  Ordinarily  this  has  been  accomplished  by 
the  resistance  which  is  offered  to  the  current  on  its  way  to  the 
periphery.  "When,  for  any  reason,  the  arterioles  are  greatly  relaxed, 
and  there  exists  at  the  same  time  high  blood-pressure,  so  much  blood 
flows  into  the  capillaries  from  the  lessened  resistance  to  its  current 
that  a  distinct  pulse  passes  along  the  capillaries  to  the  veins.  This 
pulse  is  characteristic  of  aortic  insufficiency  or  in  cases  of  atheroma 
of  the  arteries.  In  the  latter  condition  the  vessels  become  calcified 
and  rigid  and  so  behave  physically  as  inelastic  tubes. 

Cause  of  Movement  of  Blood.— T/te  force  of  the  heart  transformed 
into  arterial  tension  is  the  real  cause  of  the  movement  of  the  blood 
in  the  capillaries.  This  is  not  the  only  influence,  for  gravity  can 
exert  influences  that  are  either  favorable  or  opposed  to  the  current 
of  the  blood. 

Swiftness  of  Blood  in  the  Capillary  System. — Since  very  many 


THE  CIRCULATION. 


263 


conditions  are  capable  of  modifying  the  velocity  of  the  blood-current, 
it. is  a  very  difficult  task  to  ascertain  the  numerical  valuation  of  that 
swiftness.  If  the  time  a  corpuscle  takes  to  traverse  a  course  of  a 
known  length  be  measured  under  the  microscope,  a  fairly  accurate 
estimate  can  be  made.  Due  allowances  must  be  made  for  exaggera- 
tions from  the  magnifying  power  of  the  microscope. 

It  is  thus  estimated  that  the  corpuscles  traverse  two  indies  per 
minute  through  the  capillaries  in  man, 

BLOOD=PRESSURE— ARTERIAL  OR  VENOUS  TENSION. 

The  blood-pressure  within  any  vessel  may  be  looked  upon  as  the 
stress  upon  the  inclosed  liquid  at  the  point  of  observation.     Pressure 


Fig.  90. — Showing  the  Relative  Heights  of  Blood-pressure  in  Different 
Blood-vessels.     (  Yeo.  ) 

H,  Heart.  A,  Arteries.  a.  Arterioles.  c,  Capillaries.  Y,  Small  veins. 
V,  Large  veins.  H-V,  Being  the  zero-line,  the  pressure  is  indicated  by  the  ele- 
vations of  the  curve.  The  numbers  on  the  left  give  the  pressure  in  millimeters 
of  mercury. 


of  the  blood  has  been  placed  before  the  student's  attention  quite  fre- 
quently during  the  discussion  of  the  circulation  of  this  vital  fluid. 
Its  consideration  has  been  but  superficial,  however,  up  to  this  point. 
The  blood's  pressure  depends  upon  the  two  factors:  the  peripheral 
resistance  and  the  force  of  the  heart.  The  pressure  in  the  circula- 
tory system  varies  with  these  factors  as  variants.  Pressure  will  1)6 
greater  with  greater  heart-force  or  with  greater  peripheral  resist- 


264 


PHYSIOLOGY. 


ancc.  The  direction  of  flow  is  always  from  a  point  of  higher  to  one 
of  lower  pressure. 

The  further  the  blood  proceeds  from  that  center  of  circulatory 
motive  power,  the  heart,  the  less  becomes  the  pressure  exerted  by 
it.  It  must  be  greatest,  therefore,  in  the  arteries  emanating  from 
the  heart  and  least  in  those  veins  emptying  into  the  right  heart. 
The  decrease  is  rather  gradual  along  the  vascular  course  until  the 
vena3  cavse  are  reached;  at  their  point  of  entrance  into  the  heart 
the  blood-pressure  is  frequently  found  to  be  negative;  that  is,  below 
atmospheric  pressure. 

Thus,  the  arteries  will  be  found  to  possess  a  pressure  that  is 
peculiar  to  them,  as  do  the  capillaries  and  veins  in  their  turn.  The 
intensity  of  the  pressure  will  depend  upon  the  resistances  to  be  over- 


a  T  I  BE 

Fig.  97. — Variations  in  Pressure.      (Landois.) 

A,   Cylindrical  tube  filled  with  water.      a-6,    Outflow   tube,    along  which   are 
placed  at  intervals  the  vertical  tubes,  1,  2,  and  3,  to  estimate  pressure. 

come  and  the  vis  a  tergo  that  is  impelling  the  blood-current.  Thus 
the  arterial  pressure  depends  upon  the  relation  existing  between  the 
blood  thrown  out  by  the  ventricles  and  the  quantity  that  can  pass 
through  the  capillaries  in  the  same  time. 

Science  has  possessed  for  a  long  time  the  means  of  knowing 
what  is,  in  inelastic  tubes  which  are  the  seat  of  the  flow,  the  force 
of  afflux  for  each  point  of  their  length,  and  what,  also,  is  the  quan- 
tity of  that  force  which  has  been  consumed  by  the  resistances  known 
as  friction. 

In  order  that  the  student  may  gain  some  knowledge  of  the 
causes  that  produce  variations  in  the  pressure  as  well  as  the  means 
of  measuring  and  recording  it,  attention  will  be  turned  briefly  to 
the  physical  world  to  note  the  simplest  possible  apparatus  that  can 
convey  even  a  vague  idea  of  this  property  of  the  blood's  circulation. 


THE  CIRCULATION.  265 

Suppose  a  reservoir  full  of  liquid  to  a  certain  level,  and  from 
the  bottom  of  which  runs  a  pipe  of  uniform  caliber.  The  tubes 
which  branch  from  this  main  pipe  are  of  equal  caliber  and  are  placed 
at  equal  distances  from  one  another.  The  upright  tubes  have 
received  the  name  of  manometers.  If,  now,  there  be  a  flow  of  the 
liquid  it  will  be  because  of  a  diiference  of  pressure  at  the  reservoir 
and  outlet  due  to  gravitation.  During  this  flow  the  liquid  in  the 
various  manometers  will  contain  columns  of  the  liquid  whose  tops 
would  be  in  contact  with  a  straight  line  drawn  from  the  superior 
surface  of  the  contents  of  the  reservoir  to  the  point  of  egress.  This 
slanting  line  is  known  as  the  pressure-slope.  The  manometer  near- 
est the  reservoir  contains  the  highest  column  of  liquid,  the  next  one 
a  column  of  less  height,  etc.,  the  lowest  being  attained  in  the  upright 
tube  farthest  from  the  heart  or  reservoir. 

The  height  to  which  the  liquid  rises  in  a  manometer  sensibly 
indicates  the  intensity  of  the  force  of  afflux  at  that  point.  And,  as 
it  decreases  from  the  orifice  of  entry  to  that  of  exit,  it  must  be  con- 
cluded therefrom  that  the  force  of  the  flow  of  the  liquid  decreases 
of  itself.  It  has  been  demonstrated  in  physics  that  the  resistances 
which  liquids  meet  with  in  ducts  of  a  uniform  caliber  are  propor- 
tional to  the  length  of  the  latter.  It  follows,  therefore,  that,  when 
the  flow  is  established  in  the  tube,  the  more  distant  from  the  ingress 
a  point  of  that  tube  is,  the  more  the  liquid  which  passes  through  it 
will  have  lost  its  initial  force  in  consequence  of  resistances. 

The  more  narrow  the  caliber  of  the  tube,  the  greater  is  the 
resistance  to  the  liquid.  Up  to  the  time  of  Kev.  Stephen  Hales,  an 
English  vicar,  the  methods  of  noting  blood-pressure  were  crude  in 
the  extreme.  It  was  known  that  the  blood  exerted  considerable 
pressure  upon  the  arterial  walls,  for,  when  they  were  punctured,  an 
intermittent  jet  of  blood  arose  to  a  considerable  height,  the  latter 
depending  upon  the  proximity  of  the  wound  to  the  heart.  When  a 
vein  was  wounded  the  blood  was  noticed  to  exude  with  much  less 
force,  and  it  was  continuous,  not  intermittent. 

Hales  was  the  first  to  make  any  improvement  upon  this  rough 
movement,  which  he  did  by  inserting  a  brass  pipe  one-sixth  of  an 
inch  in  diameter  in  lieu  of  a  cannula  into  the  femoral  artery  of  a 
horse  about  three  inches  from  the  abdomen.  The  brass  pipe  in  the 
artery  was  connected  by  means  of  another  brass  pipe  to  a  glass  tube 
whose  height  was  nine  feet,  its  bore  nearly  the  same  diameter  as  the 
brass  pipe,  and  placed  vertically.  The  first  blood-pressure  experiment 
is,  perhaps,  best  depicted  in  the  words  of  Hales  himself.     He  says: 


266 


PHYSIOLOGY. 


"In  December,  1733, 1  caused  a  mare  to  be  tied  down  alive  on  her  back. 
She  was  fourteen  hands  high,  and  she  had  a  fistula  on  her  withers  and 
was  neither  very  lean  nor  yet  very  lusty.  Having  laid  open  the  left 
crural  artery  about  three  inches  from  her  belly,  I  inserted  into  it  a 
brass  pipe  whose  bore  was  one-sixth  of  an  inch  in  diameter.  To 
that,  by  means  of  another  brass  pipe,  which  was  fitly  adapted  to  it, 
I  fixed  a  glass  tube  of  nearly  the  same  diameter  and  which  was  nine 


Fig.  98. — Manometer  of  Mercury  for  Measuring  and  Registering 
Blood-pressure.      (  Yeo.  ) 

a.  Proximal  glass  tube.  6,  Union  of  the  two  glass  tubes  of  the  manom- 
eter, d.  Stop-cock  through  which  the  sodium  carbonate  can  be  introduced 
between  the  blood  and  the  mercury  of  the  manometer,  e.  The  rod  floating  on 
the   mercury   carries  the   writing-point. 


feet  in  length.  Then,  untying  the  ligature  on  the  artery,  the  blood 
rose  in  the  tube  eight  feet  three  inches  perpendicular  above  the  level 
of  the  left  ventricle  of  the  heart.  When  the  blood  was  at  its  full 
height,  it  would  rise  and  fall  at  and  after  each  pulse  two,  three,  or 
four  inches.  Sometimes  it  would  fall  twelve  or  fourteen  inches,  and 
demonstrate  at  that  point  the  same  up-and-down  vibrations,  at  and 
after  each  pulse,  as  it  had  when  it  was  at  its  full  height.  After 
forty  or  fifty  pulses  it  would  rise  to  the  former  height  again. 

"Later  I  took  away  the  glass  tube  and  let  the  blood  from  the 


THE  CIRCULATION, 


267 


artery  mount  up  into  the  open  air,  when  the  greatest  height  of  its 
jet  was  not  above  two  feet." 

Though  the  first  real  truths  concerning  blood-pressure  were 
thus  gained,  nevertheless  the  method  was  crude  and  cumbersome  in 
that  the  blood  would  soon  clot  and  an  eight-foot  column  of  blood 
was  not  easily  watched  in  its  fluctuations. 

Poiseuille,  in  1838,  introduced  into  physiological  experimenta- 
tion a  manometer  with  a  column  of  mercury.  This  instrument  is 
more  convenient  to  handle,  and  with  it  all  of  the  scientific  world  is 
acquainted  to-day. 


<ar— r^ 


Fig.  99.— Ludwig's  Kymograph.      (Yeo.) 

R,  Rotating  drum  blackened,  which  is  moved  by  the  clockwork  inclosed 
in  A  by  means  of  the  disc,  D,  pressing  on  the  wheel,  n.  The  cylinder  may  be 
elevated  or  depressed  by  the  screw,  v,  which  is  actuated  by  the  handle,  U. 

The  manometer  with  its  column  of  mercury  has  undergone  still 
further  modificatious.  Thus,  Magendie  has  employed,  under  the 
name  of  hcemometer,  an  instrument  composed  of  a  mercury  reservoir. 
Upon  this  the  blood-pressure  is  exerted,  and  it  communicates  with 
a  tube  in  which  the  metal  rises.  The  height  of  the  level  of  the  mer- 
cury in  that  single  tube  expresses  the  intensity  of  the  pressure. 

By  use  of  the  mercury  as  a  substance  against  which  the  blood 
may  expend  its  force,  the  inconvenience  of  handling  the  great  column 
of  blood  is  overcome. 

One  objection  to  the  mercury  is  that  columns  of  it,  in  their 


268 


PHYSIOLOGY. 


oscillations,  take  on  acquired  nionienium,  whicli  makes  them  pass 
beyond  the  points  which  exactly  express  the  maximum  and  the 
minimum  of  blood-pressure. 

When  such  instruments  are  used,  care  must  always  be  taken  to 
prevent  the  coagulation  of  the  blood,  by  introducing  an  alkaline  solu- 
tion into  the  points  of  the  apparatus  where  the  blood  must  penetrate. 
The  liquid  most  commonly  used  is  a  saturated  solution  of  sodium 
carbonate. 


Fig.   100. — Blood-pressure  Curve  Recorded  by  the  Mercurial 
Manometer.      (  Yeo.  ) 

c-x,  Zero-line.  y-y.  Curve  with  large  respiratory  waves  and  small  waves 
of  heart  impulse.  A,  scale  is  given  to  show  height  of  pressure  in  millimeters 
of  mercury. 

In  1847  the  study  of  arterial  tension  entered  a  new  phase,  thanks 
to  the  use  made  by  C.  Ludwig  of  the  apparatuses  with  continuous  indi- 
cations to  measure  the  variations  which  that  tension  undergoes  under 
the  influence  of  many  conditions.  The  instrument  that  he  used  is 
known  as  the  kymograph,  or  "wave-writer."  In  brief,  it  consists  of  a 
U-shaped  manometer,  in  the  open  limb  of  which  a  light  float  is  placed 
upon  the  surface  of  the  mercury.  A  writing-style  is  placed  trans- 
versely upon  the  free  end  of  the  float,  which  inscribes  its  movements, 
representing  the  oscillations  of  the  mercury,  upon  a  cylinder  wliich 


THE  CIRCULATION.  269 

revolves  at  a  uniform  rate  by  reason  of  clock-work.     There  is  recorded 
not  only  the  height,  but  its  pulsatile  and  respiratory  oscillations. 

In  looking  at  a  blood-pressure  tracing  we  find  that  the  large 
undulations  are  produced  by  respiratory  movements.  Usually  the 
ascent  is  caused  by  inspiration,  the  descent  by  expiration.  Each  of 
the  small  waves  corresponds  to  heart-action,  the  slight  ascent  to  sys- 
tole, the  slight  descent  to  diastole.  In  studying  a  tracing  it  must  be 
remembered  that  the  real  blood-pressure  is  really  twice  what  is  re- 
corded, since  the  needle  moves  through  a  space  that  represents  the 
difference  of  level  between  the  mercury  of  the  two  tubes. 


Fig.    101. — Cardiac   Manometer.      (Laiiousse.  ) 

A  and  B,  Two  burettes  of  glass  able  to  communicate  with  the  bifurcated 
cannula,  C,  by  the  aid  of  a  stop-cock  with  three  openings.  M,  Small  mercury 
manometer.    D,  Smoked  drum 

Blood=pressure  in  Man. 

Since  it  is  impossible  to  ascertain  blood-pressure  in  man  as  it  is 
practiced  in  animals,  numerous  instruments  have  been  invented  that 
can  be  used  and  applied  to  superficial  arteries  without  dissection  of 
the  tissues.  These  pieces  of  apparatus  have  been  variously  termed 
sphygmometers,  sphygmomanometers^  etc. 

Sphygmomanometer. — The  Riva-Rocci  spliygmomanometer  con- 
sists of  a  canvas  band  bound  close  about  the  arm.     Within  the  canvas 


270 


PHYSIOLOGY. 


band  is  a  rubber  bag  which  communicates  with  a  mercury  mano- 
meter and  with  the  rubber  bulb  which  produces  the  pressure.  When 
the  canvas  band  is  in  place,  the  rubber  bulb  is  rhythmically  com- 
pressed and  air  forced  into  the  rubber  bag  around  the  arm.  This 
mflated  bag  exerts  a  pressure  upon  the  arm  and  upon  the  brachial 
artery.  The  pressure  is  increased  until  the  radial  pulse  disappears 
at  the  wrist.  The  moment  the  radial  pulse  disappears,  the  mercurial 
column  indicates  the  systolic  pressure  in  the  artery  of  the  arm. 

The    instrument    of    Eiva-Eocci    gives    the    systolic    pressure. 
Mosso,  however,  invented  an  instrument  which  gives  the   diastolic 


Fig.    102. — Riva-Rocci   Sphygmomanometer. 

pressure.  The  principle  involved  in  Mosso's  instrument  is  a  regis- 
tration of  the  pulsations  of  the  artery  under  different  pressures,  and 
finding  out  under  what  pressure  maximal  pulsations  are  obtained. 
This  pressure  should  be  equal  to  the  diastolic  pressure  inside  the 
artery.  Howell  and  Brush  have  proved  this  on  the  exposed  artery 
of  a  dog. 

The  Sphygmomanometer  of  Mosso. — In  this  instrument  the 
two  middle  fingers  of  each  hand  are  placed  in  rubber  capsules  inside 
metallic  tubes,  and  the  pressure  regulated  to  obtain  the  greatest 
excursion  of  the  mercury  manometer.  In  this  instrument  water- 
pressure  is  used  outside  an  artery,  and  increased  so  as  to  exactly  bal- 
ance the  internal  pressure;  then  the  oscillation  of  the  arterial  walls 
will  be  greatest  when  they  are  free  to  move. 


THE  CIRCULATION.  271 

There  are  several  sphygmomanometers  in  this  country,  and  the 
best  is  that  of  Dr.  Erlanger. 

It  must  be  remembered  that  fallacies  exist  in  the  use  of  such  an 
instrument.  For  the  matter  is  only  too  evident  that  there  will  be 
recorded  compression  of  the  vena3  comites  of  the  artery,  the  skin 
and  surrounding  tissues.  Further,  it  is  impossible  to  tell  the  exact 
moment  when  the  distal  pulse  is  rendered  imperceptible. 

Erlanger  obtained  in  the  brachial  artery  an  average  pressure  of 
110  millimeters  during  systole  and  65  during  diastole.  He  also 
found  that  a  heavy  meal  was  followed  by  an  increased  output  of 
blood  by  the  heart,  as  revealed  by  an  increase  in  pulsc-pressure. 
This  sometimes  becomes  dangerous  to  the  degenerated  arterial  walls 
of  the  brain,  resulting  in  apoplexy. 

In  the  case  of  liealthy  young  adults,  the  pressure  in  the  brachial 
artery  ranges  between  110  and  130  millimeters  of  mercury.  Pres- 
sure attains  its  maxinmm  with  the  individual  in  the  erect  position ; 
its  minimum  when  he  assumes  the  horizontal. 

In  unconsciousness  produced  by  chloroform  the  blood-pressure 
falls  about  30  millimeters.  Alcohol  depresses  arterial  tension. 
Faivre,  by  actual  measurement  in  man  during  the  amputation  of  a 
leg,  found  the  mean  pressure  115  millimeters. 

Extremes  of  Pressure. — The  highest  pressure  is  registered  in  the 
aorta.  While  traversing  the  arteries  the  fall  in  pressure  is  very 
gradual.  Immediately  upon  its  passing  from  the  arterioles  into  the 
capillaries  and  there  meeting  great  resistance,  the  pressure  fall  is 
very  marked. 

The  blood-pressure  continues  to  fall  in  the  capillaries  and  veins 
until  the  cardiac  portion  of  venas  cava  are  reached,  when  the  Jowest 
pressure  is  registered.  As  stated  elsewhere,  this  last  pressure  may 
be  negative. 

The  causes  of  alteration  in  blood-pressure  of  arteries,  according 
to  Brunton,  are  as  follows: — 

It  may  be  raised : — 

1.  By  the  heart  beating  more  quickly. 

2.  By  the  heart  beating  more  vigorously  and  more  completely 
and  sending  more  blood  into  the  aorta  at  each  beat. 

3.  By  contraction  of  the  arterioles  retaining  the  blood  in  the 
arterial  system. 

It  may  be  depressed : — 

1.  By  the  heart  beating  more  slowly. 


272  PHYSIOLOGY. 

2.  By  the  heart  beating  less  vigorously  and  completely  and  send- 
ing less  blood  into  the  aorta  at  each  beat. 

3.  By  dilatation  of  the  arterioles,  allowing  the  blood  to  flow  more 
quickly  into  the  veins. 

4.  By  deficient  supply  of  blood  to  the  left  ventricle,  as  from  con- 
traction of  the  pulmonary  vessels  or  obstruction  to  the  passage  of 
blood  through  them,  or  from  stagnation  of  the  blood  in  the  large 
veins,  as  in  shock. 

The  blood-pressure  in  the  pulmonary  artery  is  al)out  one-third 
that  of  the  aorta. 

Respiratory  Undulations. — In  studying  a  graphic  record  of  the 
heart's  action  one  is  struck  with  the  almost  rhythmical  rise  and  fall 
of  the  general  tracing.  There  is  thus  depicted  the  condition  of  arte- 
rial pressure  conjointly  with  the  graphic  representation  of  the  heart- 
beats. They  are  produced  by  the  respiratory  movements,  and  hence 
have  been  termed  respiratory  undulations. 


Fig.    103. — Traube-Hering   Curves.      (  Fkedeeicque.  ) 

Cause. — During  inspiration  the  blood-pressure  rises;  during  ex- 
piration it  falls.  Stimulation  of  the  vasomotor  center  is  also  partly 
responsible  for  these  undulations.  This  stimulation  is  produced  by 
the  respiratory  movements  themselves,  which,  by  indirectly  causing 
the  arteries  to  contract,  raise  blood-pressure. 

Traube-Hering  Curves. — These  are  curves  which  are  higher  than 
the  regular  respiratory  undulations,  but  less  frequent.  They  are  due 
to  alterations  in  the  condition  of  the  small  arteries,  superinduced 
by  the  waxing  and  waning  at  regular  intervals  of  the  excitability  of 
the  main  vasomotor  center. 

Vagus  and  Blood-pressure. — When  the  blood-pressure  rises  in  an 
animal  the  usual  sequence  is  for  the  pulse-rate  to  be  diminished  by 
virtue  of  stimulation  to  the  cardio-inhibitory  ends  of  the  vagus.  A 
fall  in  the  blood-pressure  is  followed  by  an  increase  in  the  rate  of 
heart-action.  If  the  pneumogastrics  are  divided  the  pulse  frequency 
increases,  and  as  a  result  the  arterial  tension  rises.  If  the  vagi  are 
irritated  the  pulse-rate  falls  and  as  a  sequence  the  arterial  tension 
diminishes. 


THE  CIRCULATION.  273 

If,  however,  the  arterioles  contract,  the  pressure  rises,  and  this 
increas^e  of  tension  irritates  the  ends  of  the  vagus  and  lowers  the 
pulse-rate.  If  the  arterioles  dilate  the  pressure  falls,  and  this  low- 
ers the  tonus  of  the  vagi,  and  the  pulse  runs  faster.  The  reciprocal 
power  of  the  pulse  and  blood-pressure  to  regulate  each  other  depends 
on  normal  pneumogastrics. 

Pathological, — In  cases  of  granular  or  contracted  kidney,  sclerosis 
of  the  arteries,  and  where  digitalis  is  used  in  heart  affections,  the 
blood-pressure  is  raised.  Injected  ergotin,  by  causing  contraction  of 
the  arterioles,  also  raises  pressure,  while  morphine  lowers  the  same. 
The  blood-pressure  falls  in  the  ending  of  fevers. 

Capillary  Blood-pressure. — Von  Kries  has  estimated  the  blood- 
pressure  in  the  capillaries  of  the  ear  to  be  about  22  millimeters  of 
mercury. 

Venous  Blood-pressure. — Since  the  pressure  is  so  low  (even  nega- 
tive in  places)  within  this  system,  a  saline  solution  is  usually  sub- 
stituted in  the  manometer  for  mercury.  The  kymographic  tracing 
taken  near  the  heart  shows  the  characteristic  large  and  small  waves, 
with  this  difference,  however,  that  the  respiratory  rise  accompanies 
expiration. 

Venous  blood  is  increased  by  all  conditions  which  tend  to 
decrease  the  difference  of  pressure  between  the  arterial  system  and 
itself.  The  reverse  will  produce  diminution  in  its  tension.  General 
plethora  increases  it;  ana?mia  diminishes  it.  There  is  a  mean  nega- 
tive pressure  of  about  0.1  millimeter  of  mercury  near  the  heart.  As 
one  proceeds  from  the  heart  there  is  found  the  development  of  a  posi- 
tive pressure. 

In  the  crural  vein  the  blood-pressure  is  about  11  millimeters 
of  mercury. 

Venous  Pulse. — This  pulse  in  the  jugular  is  a  visible  sign  of  a 
circulation  in  the  veins.  The  pulse  is  due  to  the  auricular  systole, 
which  produces  not  a  reflux  but  a  temporary  arrest  in  the  flow  of 
venous  blood.  The  venous  pulse  seen  in  disease  differs  from  the 
preceding  as  regards  cause.  It  is  due  to  insufficiency  of  the  tricuspid 
valve.  Here  the  reflux  of  blood,  when  the  ventricle  contracts,  pro- 
duces the  venous  pulse. 

RAPIDITY   OF  THE  CIRCULATION. 

When  examining  the  web  of  the  frog's  foot  beneath  the  micro- 
scope it  is  clearly  discerned  that  the  rate  of  the  blood's  flow  through 
the  capillaries  is  very  much  less  than  what  it  must  be  in  the  aorta  and 

18 


274  PHYSIOLOGY. 

its  larger  1/ ranches.  That  there  should  be  differences  in  its  rate  of 
flow  depends  upon  the  same  physical  reasons  as  govern  the  rate  of 
flow  in  tubes,  namely :  resistance,  branching,  size  of  caliber,  and  the 
total  cross-sectional  area. 

If  there  were  no  friction,  the  size  of  the  vessels  would  make  no 
difference.  However,  contact  of  the  fluid  with  the  sides  of  the  vessels 
causes  a  resistance  which  is  proportionately  inverse  to  the  diameter 
of  the  vessel :    the  greater  the  diameter,  the  less  the  resistance,  etc. 

The  effect  of  branching  is  to  produce  little  eddies  and  whirls  in 
the  stream,  both  of  which  increase  the  resistance.  In  vessels  of 
greater  caliber  with  the  same  impulsive  power  behind,  the  flow  is 
slower  than  in  those  of  less  caliber. 

Perhaps,  however,  the  one  greatest  factor  influencing  the  rate 
of  flow  is  the  sectional  area  at  any  point.  With  regard  to  it  the  law 
seems  to  be  that  the  velocity  of  the  blood-current  at  any  given  point 
in  the  circulatory  system  is  inversely  proportional. 

The  arterial  system  widens  from  the  center  to  the  periphery. 
All  physiologists  admit  this  proposition,  for  their  opinion  is  founded 
upon  exact  measurements.  It  has  been  found  that,  when  there  is  an 
arterial  bifurcation,  the  area  of  the  two  branches  formed  exceeds 
that  of  the  afferent  trunk.  From  experimental  demonstration  of  the 
widening  of  the  arterial  passages,  the  comparison  of  the  arterial  tree 
to  a  cone  is  permissible;  its  summit  is  located  at  the  heart,  its  base 
at  the  periphery  of  the  body.  The  venous  system  is  similarly 
arranged,  the  apices  of  the  two  systems  meeting  at  the  heart. 

From  this  general  form  of  the  arterial  passages  it  can  be  con- 
cluded that  the  movement  of  the  blood  must  be  more  rapid  in  the 
aorta  than  in  the  vessels  springing  from  it,  and  that  the  minimum 
of  speed  must  be  in  the  smallest  arterioles.  It  is  known  that  the 
cross-sectional  area  of  the  arterioles  and  capillaries  is  from  500  to 
700  times  greater  than  that  of  the  first  portion  of  the  aorta;  there- 
fore, the  velocity  of  the  blood  in  the  capillaries  is  but  Vsoo  or  ^Aoo 
of  that  in  the  aorta. 

The  resistance  which  the  blood  meets  with  in  the  more  or  less 
shrunken  vessels  is  generally  designated  by  the  misnomer  friction. 
Physics  show  that  there  is  no  real  friction  between  the  walls  of  the 
vessels  and  the  contained  liquid.  The  exterior  layer  of  the  liquid 
is  adherent  to  the  inner  surface  of  the  tube  and  remains  perfectly 
motionless.  The  next  layers  adhere  to  one  another  less  and  less  the 
more  central  they  are.     Thus  the  swiftness  of  the  liquid  molecules 


THE  CIRCULATION. 


275 


will  not  be  the  same  in  all  parts  of  the  vessel,  the  maximum  being 
reached  at  the  center  of  the  vessel. 

Rate  in  the  Arteries. — From  the  relation  of  the  arteries  to  the 
main  central  pump,  the  heart,  very  naturally  the  velocity  of  the 
blood-flow  in  them  is  greater  than  in  the  capillary  or  venous  sys- 
tems. In  rough  terms,  the  average  velocity  in  the  large  arteries  is 
12  inches  per  second.     To  measure  the  velocity  we  employ  Ludwig's 


Fig.   104. — Ludwig's   Stromuhr.     (Landois.) 

stromuhr,  or  rheometer.  This  instrument  consists  of  two  glass 
bulbs,  1  and  2,  of  the  same  capacity.  The  ends  of  these  glass  bulbs 
have  a  common  opening  above;  below  they  are  fixed,  at  5-5',  into 
a  metal  disc.  This  disc  rotates  around  the  disc,  6-6" ,  so  that  after 
a  complete  revolution  a  bulb,  1,  communicates  with  a  cannula,  9,  and 
another  bulb,  2,  communicates  with  another  cannula,  S.  This  can- 
nula, 8,  is  fixed  in  the  central  end  and  the  other  cannula,  9,  in  the 
peripheral  end  of  the  artery  (carotid);  the  bulb,  1,  is  filled  with  oil; 
the  bulb,  2,  with  defibrinated  blood.  At  a  certain  time  the  com- 
munication through  8  is  opened,  the  blood  flows  in,  pushing  the  oil 


276  PHYSIOLOGY. 

before  it  and  passes  into  2,  while  the  blood  passes  througli  0  into  the 
peripheral  part  of  the  artery.  As  soon  as  the  oil  reaches  Jf,  the  time 
is  noted,  and  bulbs  1  and  2  are  rotated  so  that  2  takes  the  place  of 
1,  and  the  oil  is  pushed  back  into  1  again.  The  quantity  of  the 
blood  which  passes  in  a  given  time  is  calculated  from  the  time  neces- 
sary to  fill  the  bulb. 

Other  instruments  used  have  received  the  names  hcemata- 
chometer,  hcemadromometer,  dromograph,  etc. 

Rate  in  the  Veins. — Whenever  the  total  area  of  cross-section  of 
the  vascular  tree  increases,  the  velocity  of  its  contained  blood-cur- 
rent diminishes;  conversely,  as  the  cross-section  diminishes  the  flow 
becomes  proportionately  more  rapid.  The  total  section  of  the  sys- 
temic arterial  tree  reaches  its  maximum  extent  in  the  arterioles  and 
capillaries.  Along  the  venous  tree  the  cross-section  diminishes  as 
the  heart  is  neared,  but  never  becomes  as  small  as  that  of  the 
arteries.  Therefore,  the  greatest  velocity  must  exist  in  the  arteries, 
the  least  within  the  capillaries,  while  the  mean  between  the  two 
extremes  is  that  within  the  veins. 

Since  the  venous  cross-section  diminishes  as  the  heart  is  neared, 
the  velocity  of  its  blood-current  becomes  heightened  accordingly. 
However,  the  average  rate  of  venous  blood-flow  has  been  estimated 
to  be  about  9  inches  per  second. 

Rate  in  the  Capillaries. — Even  with  respect  to  the  capillaries 
the  rule  holds  good  that  the  velocity  is  inversely  proportional  to  the 
area  of  cross-section.  In  the  frog  the  velocity  has  been  estimated 
to  be  about  one  inch  per  minute ;  among  mammals  it  is  said  to  aver- 
age two  inches  per  minute. 

Marey,  from  a  study  of  the  rapidity  of  the  flow  of  blood,  has 
arrived  at  the  following  conclusions : — 

If  the  resistance  increases  and  the  output  of  the  heart  remains 
constant,  then  the  actual  tension  rises  and  the  velocity  becomes  less. 

If  the  output  of  the  heart  increases  and  the  resistance  remains 
constant,  then  both  the  tension  and  the  velocity  become  greater. 

Ludwig  and  Dogiel  state  that  the  velocity  of  the  blood  does  not 
depend  on  the  mean  blood-pressure.  They  state  that  the  velocity 
in  a  section  of  a  vessel  depends  on  (1)  the  vis  a  tergo — that  is,  the 
action  of  the  heart ;   and  (2)  on  the  peripheral  resistance. 

Duration  of  the  Circulation  as  a  Unit. — The  general  rapidity  of 
the  circulation — that  is,  how  long  a  time  an  entire  circulation 
occupies — may  be  easily  determined  experimentally  in  a  living  ani- 
mal.    This  was  first  accomplished  by  Hering,  whose  principle  of 


THE  CIRCULATION.  277 

action  was  to  compute  the  time  required  for  the  circuit  of  an 
injected,  harmless  substance.  The  substance  taken  is  one  that  may 
be  easily  recognized  by  chemical  test;  sodium  ferrocyanide  is  the 
one  least  injurious  to  the  heart.  He  injected  a  2-per-cent.  solution 
into  the  central  end  of  a  divided  jugular  vein,  and  the  time  of  injec- 
tion was  carefully  noted.  From  the  opposite  jugular  samples  were 
taken  as  quickly  as  possible,  the  time  of  each  being  noted.  When 
the  Prussian  blue  reaction  was  obtained  in  any  sample,  the  time  of 
its  withdrawal  gave  the  duration  of  the  entire  circuit.  In  this 
experiment  the  blood  containing  the  solution  passed  to  the  right 
side  of  the  heart,  through  the  lungs  to  the  left  side  of  the  heart, 
from  thence  into  the  aorta  to  be  distributed  through  the  smaller 
vessels  and  capillaries  of  the  head  and  face,  to  return  by  the  jugular 
veins. 

This  jugular-to-jugular  result  does  not  represent  the  circula- 
tion of  the  entire  blood-supply  of  the  body,  but  the  shortest  time 
that  a  drop  of  blood  may  traverse  the  shortest  pathway  along  both 
the  systemic  and  pulmonic  circulations.  It  is  impossible  thus  to 
determine  the  circulation  time  of  the  entire  blood. 

From  the  result  of  experiments  it  has  been  ascertained  that 
the  circulation  time  in  the  horse  is  31.5  seconds;  in  the  dog,  16.7 
seconds;  in  the  rabbit,  7.79  seconds. 

Another  method  is  that  of  Professor  G.  N.  Stewart.  He  injects 
into  a  rabbit  methylene  blue  per  jugular,  and  then,  watching  the 
appearance  of  the  coloring  matter  in  the  opposite  carotid,  under 
the  carotid  he  places  a  thin  sheet  of  India  rubber  and  between  this 
and  the  artery  a  little  piece  of  white,  glazed  paper.  Then,  noting 
the  time  when  blood  is  injected  per  jugular  and  the  time  of  its 
arrival  in  the  opposite  carotid,  he  determines  the  duration  of  the  cir- 
culation. In  the  rabbit  he  made  the  jugular-to-jugular  time  from 
5  to  7  seconds. 

In  man  the  time  it  takes  the  blood  to  make  a  complete  circuit  of 
the  body  is  about  32  seconds. 

COURSE  OF  BLOOD  IN  THE  VENOUS  SYSTEM. 

When  the  blood  has  undergone  within  the  general  and  pulmon- 
ary capillaries  the  changes  which  result  from  processes  of  nutrition 
and  oxidation,  it  returns  to  the  heart.  It  is  the  venous  system  which 
is  charged  with  this  centripetal  transportation. 

Has  the  action  of  the  heart  anything  to  do  with  the  progression 
of  the  venous  blood  ?     To-day,  all  the  world  recognizes  that  it  is  the 


278  PHYSIOLOGY. 

cardiac  impulsion  which,  after  having  driven  the  blood  through  the 
capillaries,  still  presides.  That  is,  the  venous  blood-current  is  main- 
tained primarily  by  the  vis  a  lergo  (force  from  behind).  In  other 
words,  it  is  what  remains  of  the  systolic  energy  of  the  heart  trans- 
mitted through  the  arteries  and  capillaries.  The  elasticity  of  the 
venous  walls  themselves  aids,  to  a  slight  extent,  the  movement  of 
the  blood  by  their  rather  feeble  contractions.  Contraction  of  the 
skeletal  muscles,  aspiration  of  the  heart  and  thorax  are  factors  also; 
the  last-named  condition  creates  the  vis  a  fronte. 

As  the  pulse-wave  is  normally  caused  to  disappear  in  the  capil- 
lary network,  so  also  the  blood-pressure  must  suffer  materially;  in 
fact,  it  continues  falling  even  along  the  course  of  the  veins  until 
the  heart  is  reached.  Nowhere  along  the  venous  system  is  the  posi- 
tive pressure  more  than  the  merest  fraction  of  what  is  found  along 
the  arterial  tree.  In  the  right  side  of  the  heart  and  the  thoracic 
portions  of  the  great  veins  the  pressure  may  even  be  negative;  that 
is,  less  than  the  atmospheric  pressure.  In  the  small  venous  radicles 
coming  from  the  capillary  system  the  blood-current  is  more  rapid 
than  in  the  capillaries  themselves,  but  far  from  the  speed  of  that 
attained  in  the  corresponding  arterioles. 

There  must  of  necessity  be  other  influences  exerted  at  this  stage, 
since  the  energy  which  the  systole  of  the  heart  has  put  forth  has 
been  greatly  expended  before  it  reaches  the  veins. 

At  the  head  of  the  list  of  factors  conducive  to  venous  flow,  other 
than  cardiac  systole,  stand  the  contractions  of  the  skeletal  muscles. 

The  contraction  of  the  muscles  aids  the  passage  of  the  venous 
flow  somewhat  as  follows:  When  pressure  is  brought  to  bear  upon 
the  vein  with  its  contents  at  any  particular  point  naturally  the  con- 
tained blood  will  endeavor  to  escape  in  two  directions.  That  escap- 
ing toward  the  capillary  system  is  soon  checked  by  the  closing  of 
the  first  pair  of  valves,  so  that  this  portion  of  the  vein  becomes 
swollen  and  distended,  but  firmly  holds  the  blood.  The  closure  of 
the  valves  allows  a  current  to  be  established  in  but  one  direction, 
and  that  toward  the  heart,  thereby  assisting  venous  flow  in  propor- 
tion to  the  extent  of  pressure  exerted.  In  the  limbs  is  found  this 
aid  to  venous  circulation.  Should  the  muscles  remain  in  a  state  of 
tetanic  contraction,  the  venous  blood  passing  out  collects  in  the  sub- 
cutaneous system,  for  it  must  be  remembered  that  particularly 
numerous  anastomoses  with  one  another,  as  well  as  the  deep  with 
the  superficial  veins,  are  characteristic  of  this  system.  That  the 
muscles  aid  venous  flow  is  nicely  demonstrated  by  the  increased  flow 


THE  CIRCULATION.  279 

from  an  incised  vein  during  contraction  of  its  adjacent  muscles 
when  performing  venesection. 

The  action  of  the  diaphragm  and  intercostals  helps  to  render 
the  intrathoracic  pressure  negative  during  inspiration;  so  that  the 
blood  is  drawn  from  the  peripheral  portion  of  the  venous  tree  toward 
the  heart;  as  some  observer  states  it,  the  blood-column  is  actually 
lifted  in  the  ascending  vena  cava. 

Another,  though  less  important,  factor  in  venous  propulsion  is 
thoracic  suction.  For  every  time  that  the  chest  expands  and  makes 
in  its  interior  an  empty  space,  air  rushes  in  to  fill  the  same.  The 
venous  blood,  situated  in  the  vicinity  of  that  cavity,  also  is  helped 
into  its  intrathoracic  veins. 

CIRCULATION  IN  THE  BRAIN. 

Dr.  Leonard  Hill  states  that  the  brain  content  of  blood  can  vary 
suddenly  only  to  a  slight  degree,  and  that  Monro's  doctrine  is  to  all 
intents  and  purposes  true.  When  the  aortic  pressure  rises  the 
expansion  of  the  cerebral  volume  can  take  place  only  to  a  certain 
limited  degree,  for,  as  soon  as  all  the  cerebro-spinal  fluid  is  driven 
out  from  the  cranium,  the  brain  everywhere  is  in  contact  with  the 
rigid  skull.  We  have  in  the  vasomotor  center  a  protective  mechan- 
ism by  which  blood  can  be  drawn  at  need  from  the  abdomen  and 
supplied  to  the  brain.  At  the  moment  of  excitation  from  the 
external  world  the  splanchnic  area  contracts  and  more  blood  is 
driven  through  the  brain.  Tlie  quantity  of  blood  in  the  brain  is  nearly 
the  same,  but  the  rapidity  of  circulation  in  the  brain  varies.  Thus, 
should  there  be  any  evidence  of  cerebral  congestion,  the  splanchnic 
fibers  dilate  the  vessels  in  its  area,  and  by  so  doing  decrease  the 
amount  sent  to  the  cavity  of  the  cranium.  Should  cerebral  anaemia 
occur,  the  reverse  will  be  the  condition  of  affairs  in  the  splanchnic 
area. 

VASOMOTOR    NERVOUS   SYSTEM. 

Thus  far  the  circulatory  system,  except  the  heart,  has  been  con- 
sidered almost  entirely  from  its  physical  standpoint:  that  it  is  a 
system  of  more  or  less  elastic  tubes  through  which  the  blood  is  pro- 
pelled by  the  action  of  the  heart.  There  was  considered  the  resist- 
ance which  its  passage  met  with,  the  pressure  exerted  by  this  vital 
fluid,  together  with  the  interpretations  and  the  physical  causes  for 
variations  in  each  function  or  property.  It  yet  remains  to  consider 
that  they  are  living  tubes,  and  that  they  and  the  heart  are  kept  in  a 


280  PPIYSIOLOGY. 

very  delicate  balance  by  reason  of  certain  physiological  mechanisms. 
The  agents  governing  their  functions  are  impulses  that  emanate 
from  the  central  nervous  system  via  certain  nerves.  The  circula- 
tory apparatus,  as  every  other  system,  or  organ,  or  part  of  the  entire 
economy,  is  under  one  management  and  direction  located  within  the 
central  nervous  system.  It  is  this  latter  system  that,  by  the  main- 
tenance of  its  functions,  produces  harmony  and  division  of  labor 
throughout  the  entire  body. 

It  has  been  previously  stated  that  the  musculature  of  the  heart 
is  under  the  guidance  of  two  sets  of  nerve-fibers:  one. set  to  restrain 
heart-action;  another  to  increase  it.  Likewise  there  are  tivo  sets  of 
fibers  which  supply  the  musculature  of  the  vessels  (particularly  the 
arterioles,  since  their  proportionate  quantity  of  circular,  unstriped 
muscular  fibers  is  greatest),  which,  together  with  their  centers,  con- 
stitute the  vasomotor  system. 

The  vasomotor  system  may  be  said,  then,  to  be  composed  of  the 
vasomotor  center,  situated  in  the  medulla,  together  with  some  acces- 
sory and  subsidiary  centers  in  the  spinal  cord,  and  vasomotor  nerves. 
The  nerves  are  divided  into  tiDo  classes,  according  as  they  increase  or 
diminish  the  caliber  of  the  arterioles:  those  which  increase  the  cali- 
ber are  vasodilators;  those  which  diminish  the  same  are  known 
as  vasoconstrictors.  All  nerves  that  in  any  way  influence  vessel- 
caliber  are  classed  under  the  general  head  of  vasomotor. 

How  the  Nerves  End. — The  manner  in  which  the  nerves  end  in 
the  walls  of  the  blood-vessels  is  an  important  subject.  According 
to  the  majority  of  histologists,  they  end  in  the  circular  muscle  of 
the  arterioles.  With  the  exception  of  the  portal  system,  there  has 
not  been  established  any  direct  proof  of  function  of  vasomotor  nerves 
in  regard  to  the  venous  system. 

Stilling,  in  1840,  knew  that  the  vascular  nerves  ran  in  the  sym- 
pathetic, and  he  named  these  nerves  vasomotors.  Claude  Bernard, 
in  1851,  found  that  after  section  of  the  cervical  sympathetic  the 
blood-vessels  of  the  ear  dilated  and  the  ear  became  warmer.  In 
1852  Brown-Sequard  discovered  that  electrical  irritation  of  the 
cranial  end  of  the  sympathetic  was  followed  by  a  contraction  of  the 
blood-vessels,  and  that  this  contraction  was  followed  by  a  cooling  of 
the  ear. 

In  1858  Bernard  found  that  when  the  chorda  tympani  was  irri- 
tated the  blood-vessels,  instead  of  being  constricted,  were  dilated. 
To  such  an  extent  did  dilatation  occur  that  the  blood  in  the  vein 


THE  CIRCULATION.  281 

acquired,  instead  of  a  blue  color,  a  red  color.  The  veins  themselves 
became  swollen  in  size. 

These  various  observations  tend  to  prove  that  there  are  two 
kinds  of  vasomotor  nerves:    vasoconstrictors  and  vasodilators. 

Functions. — Ordinarily  the  arterioles  are  in  a  state  of  tonicity — 
moderate  contraction — to  maintain  peripheral  resistance;  otherwise 
the  flow  of  blood  through  the  capillaries  would  be  intermittent 
instead  of  continuous,  as  it  normally  is.  It  is  when  this  peripheral 
resistance  is  low  that  there  appears  a  capillary  and  venous  pulse. 

In  hot  weather  the  capillaries  of  the  skin  dilate ;  in  cold  weather 
they  contract. 

Another  very  important  function  of  the  vasomotors  is  their 
regulation  of  the  amount  of  blood-supply  to  any  part,  organ,  or  gland 
of  the  economy.  That  is,  they  govern  the  amount  found  within  the 
arterioles  and  capillaries  of  the  tissues. 

The  vasoconstrictor  nerves  arise  from  a  center  in  the  medulla 
oblongata,  pass  down  the  lateral  columns,  and  establish  communica- 
tion with  minor  vasomotor  centers  in  the  spinal  cord,  and  then  from 
there  the  vasomotor  fibers  emerge  from  the  anterior  roots  to  reach 
the  blood-vessels. 

When  a  vasoconstrictor  nerve,  as  the  sympathetic,  is  cut,  the 
blood-vessels  of  the  rabbit's  ear  supplied  by  it  dilate.  This  fact  indi- 
cates that  the  circulatory  vessels  have  tonic  impulses  going  to  them 
from  the  central  nervous  system  through  the  vasoconstrictor  nerves. 

This  to7ius  of  the  vasoconstrictor  nerves  does  not  exist  in  all  vaso- 
motor nerves  to  the  same  degree.  It  is  a  variable  factor — may  be 
depressed  or  absolutely  removed.  To  decide  that  a  nerve  is  a  vaso- 
constrictor nerve,  it  becomes  necessary  to  irritate  the  nerve  with  an 
electrical  current  and  then  to  see  the  blood-vessels  supplied  by  it 
contract. 

When  tonus  exists  in  a  vasoconstrictor  nerve  and  it  is  then  cut, 
there  results  an  effect  opposite  to  that  of  an  irritation.  That  is,  there 
is  a  condition  of  dilatation  in  the  arterioles  and  capillaries.  By  this 
section  of  the  vasoconstrictors  the  volume  of  the  parts  increases  in 
direct  proportion  to  the  increased  blood-supply.  If  a  cut  be  made 
into  the  organ,  the  blood  flows  more  rapidly  than  before  there  was 
section  of  the  nerve.  The  temperature  of  the  organ  increases  and  is 
perceptibly  higher  than  that  of  the  opposite  side. 

With  increase  in  dilatation  there  is  a  concomitant  fall  in  blood- 
pressure.  If  a  large  vasoconstrictor  nerve  like  the  splanchnic  be  cut, 
then  the  blood-pressure  is  marked  by  a  most  decided  fall. 


282  PHYSIOLOGY. 

If,  now,  the  vasoconstrictor  be  irritated,  preferably  with  elec- 
tricity, phenomena  that  are  opposite  to  those  just  detailed  ensue,  I'he 
arterioles  and  capillaries  become  so  contracted  that  they  are  no  longer 
visible;  the  size  of  the  organ  supplied  by  these  nerves  diminishes;  the 
venous  blood  becomes  dark.  If  you  cut  the  organ,  less  blood  flows 
out  of  it  than  when  there  is  paralysis  of  the  constrictors  and,  there- 
fore, dilatation. 

The  vasomotor  nerves  are  always  in  a  condition  of  antagonism, 
although  the  constrictor  influence  is  by  far  the  more  powerful. 
Thus,  if  a  nerve-trunk  which  contains  both  constrictor  and  dilator 
fibers  be  stimulated,  the  first  effect  is  constriction  of  the  arterioles 
and  capillaries  supplied  by  the  artery.  This  condition  of  constriction 
lasts  for  some  time,  but  is  eventually  replaced  by  dilatation  of  the 
vessels  of  the  part.     This  dilatation  is  a  sequel,  and  is  to  be  ex- 


i'l 

/ 

i 

A  B 

Fig.  105. — Curves  Obtained  by  Enclosing  the  Hind  Limb  of  a  Cat 
in  the  Plethysmograph  and  Stimulating  the  Peripheral  End  of  the  Cut 
Sciatic  Nerve    (Bowditch  and  Warren,   1886).      (Howell.) 

The  curves  read  from  right  to  left.  In  each  case  the  vertical  lines  show 
the  duration  of  the  stimulus,  namely,  fifteen  induction  shocks  per  second  dur- 
ing 20  seconds.  Curve  A  shows  the  contraction  of  the  vessels  produced  by 
excitation  of  the  freshly  divided  nerve;  curve  B,  the  dilatation  produced  by 
an  equal  excitation  of  the  nerve  of  the  opposite  side  four  days  after  section, 
the  vasoconstrictor  nerves  having  degenerated  more  rapidly  than  the  vasodilators. 

plained  by  the  fact  that  the  vasodilator  fibers  are  less  easily  exhausted 
than  are  the  vasoconstrictor  fibers.  For,  after  separation  of  the 
vasomotor  fibers  from  the  central  nervous  system,  it  is  found  that  the 
vasodilator  fibers  do  not  lose  their  excitability  before  the  lapse  of 
from  six  to  ten  days.  The  vasoconstrictor  fibers  do  not  respond  to 
excitation  after  the  third  or  fourth  day. 

Vasoconstrictors  of  the  Head. — It  is  known  that  the  cervical 
sympa:thetic  is  the  vasoconstrictor  for  the  corresponding  side  of  the 
face,  ear,  cheeks,  lips,  brow  and  iris,  middle  ear,  and  tongue,  with  the 
submaxillary  and  parotid  glands;  in  fact,  all  parts  of  the  head  with 


THE  CIRCULATION. 


283 


the  exception  of  the  brain  are  supplied  by  it  with  its  corresponding 
sympathetic.  Now,  these  vasoconstrictors  do  not  arise  from  the 
sympathetic  ganglia,  but  spring  from  the  spinal  cord  by  means  of 
their  rami  communicantes.  The  fibers  that  are  destined  for  the 
supply  of  the  head  and  neck  proceed  to  the  first  thoracic  ganglion 
and  end  in  the  superior  cervical  ganglion,  whence  postganglionic 
fibers  emerge  by  nervous  plexuses  that  arise  from  this  ganglion,  and 
reach  their  respective   destinations. 

Vasoconstrictors  of  the  Extremities. — The  fibers  that  are  in- 
tended for  the  supply  of  the  skin  area  of  the  body — head,  limbs, 
and  trunk — pass  back  by  the  rami  communicantes  to  be  distributed 
to  these  parts  with  the  other  spinal  nerve-fibers. 


Lai  Ao  74%  Kg. 


Fig.   106. — Effect  of  Irritation  of  the  Splanchnic  Nerve  on  the  Aortic 
Pressure.     (  Gley.  ) 

Dog  with  medulla  divided.     Pr,   lat.   Ao,  Aortic   pressure.     S,   Time  in  sec- 
onds.    E,  Faradic   irritation  of  the  peripheral  end  of  the   left  splanchnic. 

The  origin  of  the  constrictors  of  the  anterior  extremities  is 
probably  from  the  middle  part  of  the  dorsal  segment  of  the  spinal 
cord.  As  to  the  peripheral  course  of  these  nerves,  a  part  of  them  run 
with  the  nerves  of  the  arm  and  from  these  to  the  blood-vessels,  while 
a  part  run  directly  from  the  sympathetic  in  the  plexuses  to  spin 
around  the  blood-vessels  and  their  branches.  The  vasoconstrictors 
of  the  posterior  extremities  have  given  more  definite  results,  and  are 
found  to  spring  from  the  cord  in  conjunction  with  the  eleventh, 
twelfth,  and  thirteenth  dorsal  nerves  of  animals,  as  well  as  the  first 
and  second  lumbar  nerves  of  animals.  The  constrictors  unite  with 
the  large  nerve-trunks  and  with  their  branches  go  to  the  extremities. 

Vasoconstrictors  of  the  Abdominal  Viscera. — The  fibers  for  the 


284  PHYSIOLOGY. 

interior  of  the  economy  pass  into  the  various  plexuses  of  the  sympa- 
thetic nerves  in  the  thorax,  abdomen,  and  pelvis,  to  be  distributed  to 
the  vessel-walls  of  the  various  viscera  contained  within  these  several 
cavities.  The  grouping  includes  the  most  important  vasomotor 
nerves  of  the  body,  the  splanchnics. 

If  one  splanchnic  be  cut  in  the  abdominal  cavity,  the  blood- 
pressure  sinks  30  or  40  millimeters;  if  the  second  be  cut  the  pres- 
sure immediately  drops  to  10.  If  the  peripheral  end  of  the  cut 
nerve  be  irritated,  the  aortic  pressure  ascends  and  reaches  as  great  a 
height  as  it  had  before  section.  Through  the  paralysis  of  the 
abdominal  vessels  the  portal  system  is  filled  with  blood,  the  small 
intestinal  vessels  are  strongly  injected,  the  blood-vessels  of  the 
kidneys  are  dilated,  and  the  renal  tissue  is  red  and  congested. 

By  these  experiments  it  was  established  that  the  splanchnic  is 
the  most  important  of  all  the  vasoconstrictor  nerves,  and  therefore  an 
important  regulator  of  the  blood-pressure.  The  constrictors  of  the 
splanchnics  all  arise  from  the  tenth  dorsal  to  the  third  lumbar  inter- 
costal nerves.  The  splanchnics  supply  vasomotor  fibers  to  the  stom- 
ach, bowels,  and  kidneys.  Irritation  of  one  splanchnic  is  sufficient 
to  cause  vasoconstriction  in  both  kidneys. 

The  viscera  receive  vasoconstrictor  fibers  from  other  sources,  as 
the  vagus.  Two  weeks  after  section  of  both  splanchnics  beneath  the 
diaphragm,  the  blood-pressure  is  again  found  to  be  the  same  as  that 
of  a  normal  animal. 

The  elevation  of  a  patient  in  bed  may  lead  to  a  faint,  because 
the  heart  in  a  reclining  position  and  the  abdominal  reservoir  of  blood 
are  on  the  same  plane;  but  the  erect  position  increases  the  work  of 
the  heart  because  the  abdominal  reservoir  of  blood  is  lower. 

Vasoconstrictors  of  the  Lungs. — When  the  central  end  of  the 
splanchnic  is  irritated  the  blood-pressure  rises  in  the  arteries  of  the 
lungs,  since  a  greater  amount  of  blood  is  driven  from  the  inferior 
vena  cava.  Similarly,  an  obstructive  lesion  of  the  left  heart  will 
elevate  blood-pressure  in  the  lungs.  But  direct  observation  shows 
that  the  vasoconstrictors  of  the  lungs  are  not  strongly  developed. 

Vasodilators. — The  vasodilators  originate  from  a  principal  cen- 
ter, located  in  the  medulla  oblongata,  and  from  subsidiary  centers 
distributed  throughout  the  spinal  cord.  As  a  rule,  these  nerves  are 
mingled  with  the  vasoconstrictors;  but  there  are  exceptions.  Their 
inclination  is  to  emerge  through  the  cerebro-spinal  nerves,  while  the 
constrictors  are  generally  mixed  with  the  great  sympathetic  system. 
Their  region  of  egress  is  not  so  limited  as  that  of  the  vasoconstrictors, 


THE  CIRCULATION.  285 

since  the  nervi  erigentes  originate  as  low  down  as  the  second  and 
third  sacral  nerves,  while  the  chorda  tympani  is  a  branch  of  the 
seventh  cranial  nerve.  The  chorda  tympani  and  the  nervus  erigens 
are  pure  vasodilator  nerves :  that  is,  they  contain  no  vasoconstrictors. 

While  the  vasodilators  usually  emerge  through  the  cerebro-spinal 
nerves,  the  student  must  remember  that  the  distributions  of  the  two 
nerves  are  far  different. 

All  vasomotor  nerves  are  distributed  to  unstriped,  involuntary 
muscles;  spinal  nerves  to  striped,  voluntary  muscles.  The  former 
are  always  characterized  by  being  ganglionated ;  in  other  words, 
possessing  cell-stations,  or  relays,  in  their  course  from  the  central 
nervous  system  to  the  muscular  fibers  which  they  govern. 

The  vasodilator  nerves  behave  very  similarly  to  the  cardiac 
branches  of  the  vagus,  for,  when  both  are  stimulated,  the  result  pro- 
duced is  inhibition  and  relaxation.  Vasodilation  results  from  direct 
stimulation  of  the  center  in  the  medulla.  Thus,  during  asphyxia  the 
strongly  venous  blood,  while  it  stimulates  the  vasoconstrictor  cen- 
ter so  as  to  diminish  the  caliber  of  the  splanchnic  area,  also  stimu- 
lates the  dilator  center  to  produce  relaxation  of  the  cutaneous  ves- 
sels.    Xicotine  is  said  to  be  a  powerful  excitant  of  the  vasodilators. 

Recognition. — It  is  easy  to  recognize  a  vasodilator  nerve  when 
it  contains  no  other  fibers.  But,  should  it  be  mixed  with  vasocon- 
strictors going  to  the  same  organ,  it  becomes  necessary  to  make  spe- 
cial arrangements.  These  are  occasioned  by  the  fact  that  the  vaso- 
constrictors usually  overcome  the  dilators.  However,  the  constrictors 
become  tired  more  quickly,  and  after  they  are  exhausted  the  vaso- 
dilators act. 

By  warming  or  cooling  an  extremity  with  water,  the  experi- 
menter can,  on  irritating  a  nerve,  obtain  a  dilatation  or  a  narrowing 
of  the  blood-vessels  supplied  by  it.  When  in  the  same  nerve  two 
kinds  of  vasomotors  rim,  then  by  the  same  irritation  in  warming  the 
foot  there  is  obtained  a  contraction  of  the  vessels,  and  in  the  second 
place  a  dilatation  on  cooling  the  foot. 

Differences  in  Two  Kinds  of  Nerves. — Vasomotor  nerves  present 
differences  in  their  actions  dependent  upon  division  and  degeneration 
in  the  same.  After  degeneration,  an  irritant  to  a  nerve  calls  out 
vasodilation,  while  to  a  nerve  in  the  fresh  state  the  same  irritant 
produces  a  primary  vasoconstriction. 

By  variation  in  the  frequency  and  strength  of  the  irritation 
there  is  afforded  a  means  to  differentiate  the  two  kinds  of  nerves 
which  mav  traverse  the  same  nerve  trunk.     The  vasodilators  are  ex- 


286  PHYSIOLOGY. 

cited  by  weak  currents  and  slow  rhythm.  The  vasoconstrictors  are 
irritated  by  stronger  currents  and  greater  frequency  of  irritation. 

Path  of  Vasodilator  Nerves. — The  dilators  of  the  submaxillary 
glands  and  tongue  come  from  the  facial  to  pass  along  the  chorda 
tympani  to  the  gland.  To  reach  the  anterior  two-thirds  of  the 
tongue  the  vasodilators  traverse  the  lingual;  to  supply  the  posterior 
third  the  course  is  along  the  glosso-pharyngeal. 

The  mucous  membrane  of  the  cheek,  lips,  and  gums,  as  well  as 
of  the  nasal  openings,  receive  their  vasodilators  from  the  trigeminus. 

The  vasodilators  of  the  anterior  extremities  arise  from  the  fifth 
and  eighth  dorsal  nerves.  The  posterior  extremities  receive  their 
supply  of  vasodilators  from  the  second  to  the  third  lumbar  nerves. 

The  splanchnic  nerves  also  contain  vasodilator  fibers.  Thus  the 
cervical  sympathetic  and  splanchnics,  which  have  always  been  re- 
garded as  great  vasoconstrictors,  are  also  rich  in  vasodilators. 

Muscles  are  supplied  only  with  vasodilator  nerves. 

Theory  of  Vasodilator  Action. — The  vasodilators  act  upon  the 
circular  arterial  muscle  directly.  How  they  act  is  still  hypothetical. 
Since  physiologists  know  of  no  muscle  through  whose  contraction 
the  blood-vessels  become  more  dilated,  it  is  assumed  that  vasodilation 
is  due  to  a  paralysis  of  the  circular  fibers  of  the  vessels.  That  is,  the 
dilators  must  be   inhibitory   or   vaso-inhibitory  nerves. 

The  tonus  of  a  blood-vessel  depends  partly  upon  impulses  from 
the  central  nervous  system  via  the  vasoconstrictors.  It  is  upon  the 
circular  muscles  that  the  dilators  are  supposed  to  exert  an  inhibitory 
action. 

Frequent  allusions,  during  the  discussion  of  the  vasomotor  sys- 
tem, have  been  made  to  the  effects  of  experiments  upon  various  vaso- 
motor nerves.  They  have  been  nearly  all  performed  upon  animals, 
and  consist,  in  the  main,  of  section  and  excitation  of  various  kinds: 
electrical,  thermal,  etc.  By  these  means  much  has  been  learned  con- 
cerning this  very  important  system — important  to  the  physician  as  a 
means  of  explaining  many  pathological  conditions. 

Vasomotor  Centers. — The  main  vasomotor  center  lies  in  the  floor 
of  the  fourth  ventricle  in  its  gray  matter.  It  is  located  on  each  side 
of  the  median  raphe,  and  extends  three  millimeters  from  a  little 
above  the  nib  of  the  calamus  scriptorius  to  near  the  corpora  quad- 
rigemina.  Its  position  was  determined  by  noting  that  when  it  was 
destroyed  there  was  a  lack  of  tonicity  displayed  by  all  of  the  arteri- 
oles, with  a  consequent  fall  in  blood-pressure.  When  this  same  area 
was  stimulated  all  of  the  arterioles  were  constricted,  giving  a  rise 


THE  CIRCULATION. 


287 


in  blood-pressure  as  a  sequel.  Section  of  the  cervical  spinal  cord 
permits  all  the  arterioles  to  dilate  as  the  main  vasomotor  center  has 
been  cut  off  and  the  blood-pressure  falls  to  10  millimeters. 

Spinal  Vasomotor  Centers. — Experiments  demonstrate  that 
with  the  destruction  or  paralysis  of  the  main  center  there  results  a 
drop  in  blood-pressure ;  if,  however,  the  animal  be  kept  alive  by  arti- 
ficial respiration,  after  a  variable  length  of  time  the  arterioles  regain 
their  tonicity  and  there  is  a  corresponding  rise  in  pressure.  This 
phenomenon  is  accounted  for  by  the  presence  of  minor  or  subsidiary 
centers,  which  in  the  emergency  have  risen  in  their  functional  abili- 
ties. These  minor  vasoconstrictor  centers  exist  in  the  spinal  cord. 
They  may  be  excited  in  a  reflex  manner  by  means  of  strychnine  (Ott 
and  TClapp). 


\,^'yx^\^^ 


±'ig.  1U7. — Carotid  Pressure  in  Curarized  Dog  after  Section  of  Medulla 
A,  and  after  Destruction  of  the  Cord  B.      (Gley.) 
Normal  pressure  was  120  millimeters.     After  section  of  the  medulla  it  fell 
to  66  (4).    After  destruction  of  spinal  cord  it  fell  to  40  millimeters  (B). 

Upon  destruction  of  the  cord  there  follows  a  second  fall  of  pres- 
sure, with  dilatation  of  the  arterioles.  The  spinal  vasoconstrictor 
centers  exist  in  the  upper,  dorsal  part  of  the  spinal  cord. 

The  vasoconstrictor  center  is  in  a  state  of  permanent  excitation, 
which  produces  vascular  tonus;  this  is  not  the  case  with  the  vaso- 
dilator center. 

In  a  totally  relaxed  vascular  system  there  is  no  possible  circula- 
tion— the  blood  stands  still.  During  extreme  dilatation  the  heart  re- 
ceives but  little  blood,  so  that  but  very  little  is  driven  out  of  it  during 
systole.  Hence  the  tonus  of  the  blood-vessels  is  a  necessary  condition 
for  the  circulation. 

The  tonus  of  the  veins  is  dependent  upon  the  central  nervous 
system,  and  is  quite  as  important  as  is  that  of  the  arteries. 

The  vascular  tonus  is  continually  a  seat  of  slight  fluctuations,  of 
which  the  most  important  when  depicted  graphically  constitute  the 


288  PHYSIOLOGY. 

curves  of  Traube.  The  curves  are  the  products  of  oscillations  of  the 
vascular  tonus.  The  oscillations  are  caused  by  variations  in  the 
automatic  excitation  of  the  vasoconstrictor  centers.  (See  "Traube- 
Hering  Curves.") 

The  vasoconstrictor  center  is  excited  during  dyspnoea  and  as- 
phyxia. This  occurs  on  account  of  the  accumulation  of  carbonic  acid 
in  the  blood.  This  action  explains  why  the  arteries  in  the  cadaver 
are  free  from  blood.  Strychnine,  nicotine,  and  Calabar  bean  also 
excite  the  vasoconstrictor  center. 

Advantages  of  Vessel  Innervation. — By  reason  of  vascular  tonic- 
ity the  diameters  of  the  vessels  are  a  trifle  too  small  to  contain  all 
the  blood;  so  that  the  vascular  walls  are  obliged  to  dilate.  The  result 
is  pressure  and  circulation  of  the  blood. 

When  various  organs  and  parts  of  the  body  are  in  activity  they 
require  an  excess  of  blood.  This  surplus  is  furnished  by  a  dilatation 
of  the  capillaries  of  the  part.  Ludwig  compared  the  vasomotor  cen- 
ters to  turn-cocks  in  a  great  city.  They  turn  off  the  water-supply 
from  one  district  and  at  the  same  time  turn  it  on  in  another. 

As  previously  stated,  the  cutaneous  circulation  regulates  the 
losses  of  heat. 

When,  from  the  influence  of  cold,  the  capillaries  of  the  skin  are 
narrowed,  the  internal  organs  are  congested.  Under  the  action  of 
heat  the  skin  is  congested  and  the  internal  organs  made  ansmic. 
This  increase  in  the  blood-supply  in  those  parts  where  needed  has 
been  ingeniously  demonstrated  by  Mosso.  He  placed  a  man  upon 
a  very  large  board  which  was  most  delicately  balanced  at  its  center. 
By  use  of  it  he  demonstrated  that  whenever  the  man  began  to  think 
the  increased  blood-supply  in  his  brain  caused  the  head  to  go  down 
and  the  heels  to  rise  up. 

Vasomotor  Centers  Reflexly  Excited. — Like  the  cardiac  nerves, 
so  the  vasomotor  nerves  of  all  parts  of  the  body  may  be  excited 
reflexly. 

We  have  reflex  action  in  making  lines  upon  our  skin  with  a 
blunt  instrument,  in  the  warming  of  the  skin,  in  the  vascular  injec- 
tion upon  opening  of  the  abdominal  cavity,  and  in  the  vascular 
dilatation  of  the  vessels  of  the  pia  mater  of  the  brain  when  the  skull 
cavity  is  opened. 

By  irritation  of  the  mucous  membrane  of  the  nose  there  is  seen 
a  vascular  disturbance  of  the  whole  head.  If  one  hand  be  plunged 
into  ice-water,  the  blood-vessels  of  the  opposite  hand  also  contract. 
Thus,  irritation  of  any  sensory  nerve  in  the  body  causes,  as  a  rule, 


THE  CIRCULATION. 


289 


a  contraction  of  the  blood-vessels,  and  especially  those  supplied  by 
the  splanchnics.  The  blood-vessels  of  the  skeletal  muscles,  as  a  rule, 
dilate  after  irritation.  With  the  single  exception  of  the  nervous 
depressor,  irritation  of  any  sensory  nerve  is  followed  by  a  rise  of 
blood-pressure.  The  rise  which  is  created  depends  upon  the  strength 
and  nature  of  the  stimulus.  During  this  condition  there  is  vasocon- 
striction of  the  splanchnic  vessels,  while  at  the  same  time  the  blood- 
vessels of  the  skin  and  muscles  are  more  or  less  dilated.  The  reflexes 
that  depress  the  arterial  tension  are  due  to  the  nervous  depressor. 
This  condition  of  depression  is  due  to  a  vasodilation  of  the  arterioles, 
especially  in  the  vessels  supplied  by  the  splanchnics. 


Pr. 

s 

■■■1 

Fig.  108. — Elevation  of  Arterial  Pressure  by  Vasoconstriction.     A  result 
of  irritation  of  the  central  end  of  sciatic  in  curarized  dog.      (Hedon.  ) 

Pr,  Carotid  pressure.     8,   Signal-magnet  tracing. 


Hence,  in  the  reflex  relation  of  the  afferent  nerves  to  the  vaso- 
motor centers  there  are  two  kinds  of  flbers,  pressor  and  depressor. 
(1)  The  pressor  fibers  cause  a  vascular  narrowing,  due  to  a  reflex 
stimulation  of  the  vasoconstrictor  center.  (2)  The  depressor  fibers 
cause  dilatation  of  the  arterioles  and  a  fall  of  arterial  blood-pres- 
sure, due  to  reflex  inhibition  of  the  vasoconstrictor  center,  as  with 
the  nervous  depressor. 

There  are  also  reflex  vasodilator  fibers,  which  lower  arterial 
blood-pressure  by  a  stimulation  of  the  vasodilator  center,  as  in  the 
congestion  of  erectile  tissue  and  the  afflux  of  blood  to  glands  in 
activity. 

The  vasomotor  changes  can  be  studied  by  means  of  instruments 
which  register  the  changing  volume  of  a  part  at  each  systole  of  the 

19 


290 


PHYSIOLOGY. 


heart  and  the  varying  diameter  of  the  arterioles.     These  instru- 
ments arc  known  by  the  names  of  plethysmograph  and  oncometer. 

Pathological  Conditions  of  Circulation. — In  mitral  regurgita- 
tion the  dilatation  and  hypertrophy  of  the  left  side  of  the  heart 
are  due  to  the  blood  running  back  from  the  ventricle  at  each  systole. 
This  state  of  affairs  keeps  the  auricle  overfilled  and  the  backing  of 


Fig.    109. — Pick's  Plethysmograph.      (From  Tigerstedt's  "Human 
Physiology,"  copyright  1906,  by  D.  Appleton  and  Company.) 

ae,  Glass  cylinder.      m,  rubber  band  to  close  the  glass  cylinder,     r,  s.  Register- 
ing  manometer. 

the  blood  causes  congestion  in  the  pulmonary  capillaries,  which 
results  in  cough  and  dyspnoea. 

Sudden  death  can  result  from  a  thrombus  of  the  coronary  artery 
or  an  obliterating  arteritis  of  this  vessel. 

Hemicrania  is  due  to  unilateral  contraction  of  the  carotid 
branches  going  to  the  brain.  In  exophthalmic  goiter  the  vasomotor 
system  is  implicated. 


THE  CIRCULATION.  291 

The  secretion  of  the  urine  is,  to  a  great  extent,  under  the  var}-- 
ing  arterial  tension  due  to  vasomotor  activity.  In  fever  the  vaso- 
motor system  is  concerned  in  the  flushing  of  the  face  and  body. 

Pharmacological. — Adrenalin  greatly  elevates  blood-pressure  by 
an  action  on  the  muscular  structure  of  the  arterioles,  or,  according 
to  Langley,  by  an  action  on  the  myoneural  substance.  Amyl  nitrite 
or  nitroglycerin  lowers  arterial  tension  chiefly  by  an  action  on  the 
walls  of  the  arterioles.  Adrenalin,  when  given  witli  nitroglycerin, 
overcomes  its  action  on  blood-pressure. 

IMMUNITY. 

Normal  sera  may  contain: — 

1.  Antiferments  (blood-serum  prevents  the  ferments  from  act- 
ing as  trypsin  on  proteids  or  a  mixture  of  pancreatic  juice  and 
enterokinase,  because  the  kinase  is  neutralized). 

2.  Antitoxins. 

3.  Cytotoxins  (cell-destroyers)  include  haemolysis.  These  bodies 
are  composed  of  complement  and  an  immune  body  or  amboceptor). 

4.  Agglutinins. 

5.  Precipitins. 

ZYMOIDS.i 

There  are  a  certain  number  of  substances  contained  in  the  cul- 
tures of  microbes  which  may  be  in  the  liquids  of  the  organism,  and 
notably  in  the  blood-serum  of  normal  animals  and  in  animals  vacci- 
nated against  certain  microbes  or  their  filtered  cultures,  which  have, 
with  the  ferments,  a  certain  numher  of  common  properties.  Such  bodies 
are  the  microbian  toxins,  the  venoms  of  serpents,  the  antitoxins,  the 
agglutinins,  the  precipitins,  the  bacteriolysins,  the  hsemolysins,  etc. 
Because  of  certain  analogies  to  enzymes,  they  have  been  called 
enz}Tnoids.  Toxins  are  the  nonalkaloidal  poisons  produced  by 
microbes  or  secreted  by  the  animal  or  vegetable  cell.  These  toxins 
are  divided  into  two  kinds:  (1)  the  toxalbumins,  cellular  secretions 
destroyed  by  heat  at  70°  C,  but  not  coagulating;  they  do  not  act 
except  after  a  period  of  incubation,  always  long,  as  the  toxins  of 
diphtheria,  of  tetanus,  etc.;  (2)  the  toxproteins,  derived  from  cells 
coagulating  by  heat,  acting  upon  the  organism,  and  acting  without 
a  period  of  incubation ;  these  are  the  venoms,  the  proteins  of  plague 
and  cholera.     We  have  also  vegetable  toxalbumins,   as  abrin  from 


^In  the  preparation  of  this  article  I  have  drawn  on  Arthus,  "Chemie 
Physiologique." 


292  PHYSIOLOGY. 

jequirity,  ricin  from  castor-oil  seeds,  rubin  from  the  extract  of  the 
bark  of  the  acacias.  These  bodies  are  zymoids.  The  toxalbmnins 
always  have  a  period  of  incubation.  The  phenomena  shown  are  all 
physiological  phenomena;  an  infinitely  small  quantity  of  toxalbumin 
is  able  to  cause  phenomena  infinitely  great.  We  should  remember 
that  certain  microbian  products,  as  tuberculin  or  mullein,  resist  the 
prolonged  action  of  100°  C.  without  alteration. 

The  toxalbumins  and  venoms  have  other  common  biological 
properties. 

ANTITOXINS. 

It  is  possible,  by  repeated  injections  of  toxalbumins  or  venoms 
in  increasing  doses,  to  imnnniize  the  animal  against  the  toxic  action  of 
doses,  a  thousand  times  mortal,  of  the  toxalbumin  or  venom.  The 
immune  animals  furnish  an  antitoxic  serum.  The  toxalbumins  or 
venoms  when  swallowed  are  harmless;  injected  under  the  skin,  very 
active.  Like  the  ferments,  the  toxins  are  destroyed  by  a  relative 
low  temperature,  about  70°  C.  They  are  precipitated  by  alcohol,  and 
they  dialize  with  difficulty.  If  in  a  test-tube  you  mix  the  toxin  and 
the  antitoxic  serum  in  proper  proportions,  the  mixture  is  harmless 
to  the  animal  when  injected,  but  this  countereffect  requires  a  certain 
time  for  its  accomplishment.  These  facts  show  that  the  antitoxins 
resemble  ferments;  that  is,  they  are  soluble,  precipitable,  and  dialize 
like  enzymes,  but  are  not  enzymes.  The  basis  of  Ehrlich's  theory  is 
that  poison  and  counterpoison,  toxin  and  antitoxin,  directly  combine 
in  any  given  quantity. 

The  stable  benzene  ring  and  the  less  stable  side-chains  of  the 
benzene  derivatives  suggested  to  Ehrlich  that  living  cells  also  con- 
sist of  a  stable  center  and  less  stable  side-chains.  The  side-chains 
enable  the  cell  to  form  chemical  combinations  with  foodstuffs  and 
other  bodies  that  have  atom  groups  having  a  chemical  affinity  with 
the  atom  groups  in  the  side-chains. 

H  H 

\  / 

C  =3  C 

/  \ 

H  — C  C  — H 

X  // 

C-— c 

/     \ 

H  H 

Benzene  nucleus  or  ring.  Benzene. 


\ 

/ 

c  = 

=  c 

/ 

\ 

—  c 

c  — 

X 

// 

c- 

-c 

/ 

\ 

THE  CIRCULATION.  293 

Ehrlich  showed  further  that  for  each  poison  one  can  develop  a 
counterpoison  by  the  process  of  immunizing,  which  has  two  groups 
which  are  concerned  in  the  combination  with  the  counterpoison  or 
antitoxin.  One  of  these,  the  haptophore  group,  is  the  combining 
group  proper;  the  other,  tlie  toxophore  group,  is  the  carrier  of  the 
poison.  A  poison  molecule  might  lose  the  one,  the  toxophore  group, 
and  still  be  capable,  by  means  of  its  haptophore  group,  of  combining 
with  antitoxin.  For  a  poison  to  be  toxic  to  an  organism — that  is, 
in  order  that  the  toxophore  group  be  able  to  act  destructively  on  a 
cell — it  is  necessary  for  the  haptophore  group  of  the  poison  to  com- 
bine with  the  cell.  The  side-chains  are  able  to  combine  with  the 
greatest  variety  of  foreign  substances  and  convert  them  into  nour- 


C.  D. 

Fig.  110. — Stages  in  Widal  Reaction.     (After  Robin.) 

ishment  suitable  to  the  requirements  of  the  active  central  body. 
These  side-chains  are  comparable  to  the  pseudopodia  of  the  amoeba 
which  engulf  food  particles  and  assimilate  the  same  for  the  imme- 
diate use  of  the  organism.  In  order  that  any  substance  may  com- 
bine with  these  side-chains,  it  is  necessary  that  certain  very  definite 
relations  exist  between  the  combining  group  of  the  substance  and 
that  of  the  side-chain.  The  relation  must  be  that  of  lock  and  key; 
that  is,  the  two  groups  must  fit  accurately. 

AGGLUTININS. 

If  we  cultivate  a  vibrio  of  cholera  upon  gelatin,  and  after 
twenty-four  hours  put  the  culture  in  a  saline  solution  1  to  100,  we 
obtain  a  homogeneous  and  stable  emulsion,  in  which  the  vibrios 
retain  their  activity.  If  to  this  emulsion  we  add  a  small  quantity 
of    blood-serum    (of    a    rabbit    or    guinea-pig)    strongly   immunized 


294  PHYSIOLOGY. 

against  the  vibrio  of  the  emulsion  by  the  intra-peritoneal  injection, 
we  will  see  under  the  microscope  that  the  vibrios  lose  their  mobility 
and  unite  in  masses  of  greater  or  less  size,  agglutinate,  so  to  speak. 
This  agglutination  augments  until  the  mass  becomes  voluminous. 
This  agglutination  is  not  a  necessary  result  of  the  vitality  of  the 
vibrios;  it  is  just  as  easily  produced  with  emulsions  of  dead  vibrios. 
The  agglutinating  serum  acts  most  energetically  at  55  or  60°  C. 
The  active  substance  in  the  serum  is  precipitated  by  alcohol,  it  is 
not  destroyed  by  drying  at  a  low  temperature,  and  it  dissolves  in 
water  and  glycerin.  These  are  the  properties  also  of  enzymes.  The 
active  substance  here  is  agglutinin.  Widal  Reaction. — The  typhoid 
patient's  serum  gives  an  agglutinating  serum  for  homogeneous  cul- 
tures of  the  typhoid  bacillus. 

PRECIPITINS— TSCHISTOVITCH=UHLENHUTH  TEST. 

When  you  inject  under  the  skin  or  into  the  peritoneum  of  an 
animal  a,  of  species  A,  some  cubic  centimeters  of  blood-serum  of 
species  B,  and  repeat  the  injection  four  or  five  times  in  the  space 
of  five  or  six  days,  we  find  th^t  blood-serum  of  the  animal  a  has  the 
property,  when  mixed  with  the  serum  of  the  animal  of  species  B,  to 
cause  a  fine  precipitate  at  the  bottom  of  the  mixture.  If  in  place 
of  the  injection  of  blood-serum,  under  the  same  conditions  we  inject 
the  albuminoid  substances  of  the  serum  separated  by  precipitation 
by  ammonium  sulphate  and  dissolved  in  saline  1  to  100,  we  find  that 
the  serum  of  a  has  acquired  the  property  of  precipitating  the  serum 
of  the  animal  of  the  species  B  as  before.  This  fact  is  used  to 
determine  human  blood  by  injecting  the  serum  of  human  blood  into 
rabbits  or  dogs.  We  thus  obtain  precipitants  for  human  blood,  a 
medico-legal  test.  This  precipitate  is  destroyed  by  heat  over  100°  C; 
it  is  not  destroyed  by  drying  at  a  low  temperature;  it  is  soluble  in 
water;  it  is  precipitated  by  alcohol  and  by  the  salts  precipitating 
globulins.    These  are  the  properties  of  enzymes.    It  may  be  a  zymoid. 

CVTOTOXINS. 

As  to  cytotoxins,  we  have  seen  in  transfusion  that  blood  foreign 
to  an  animal  dissolves  its  corpuscles  (or  cells) ;  hence  are  called 
hsemolysins.  The  leucotoxins  dissolve  white  blood-corpuscles.  The 
haemolysins  act  by  separating  the  haemoglobin  from  the  stroma  of 
the  blood-corpuscles,  making  blood  "laky."  In  fundamental  charac- 
ters the  haemolysins,  both  natural  and  artificial,  correspond  to  the 
bacteriolysins. 


THE  CIRCULATION.  295 

If  you  introduce  into  the  peritoneal  cavity  of  a  guinea-pig, 
which  is  strongly  immunized  against  a  vibrio  of  cholera,  an  emulsion 
of  this  vibrio  obtained  by  putting  into  a  saline  solution,  1  to  100, 
a  24-hour  culture  of  the  cholera  vibrio  upon  gelatin,  it  will  be  found, 
on  withdrawing  a  little  of  the  peritoneal  fluid,  after  half  an  hour, 
that  the  vibrios  injected  have  lost  their  motion,  are  transformed  into 
lumps,  and  are  broken  up  into  granules.  This  is  known  as  the  phe- 
nomenon of  Pfeiffer.  This  property  of  the  serum  of  a  vaccinated 
animal  is  due  to  the  presence  of  a  substance,  a  bacteriolysin,  or  lysin, 
or  cytolysin;  the  complement  and  the  intermediary  body  make  up 
the  cytolysin. 

It  has  been  demonstrated  that  the  bacteriolytic  cholera  serum 
contains  two  distinct  substances,  acting  one  after  the  other  in  the 
bacteriolysis,  one  substance  destroyed  below  60°  C.  and  existing  in 
normal  serum  as  well  as  in  cholera  serum,  and  another  substance 
resisting  a  temperature  of  60°  C.  and  not  existing  except  in  the 
cholera  serum.  The  specific  substance  has  been  called  a  thermostable 
substance,  because  it  resists  a  temperature  of  60°  C;  and  a  sensitiz- 
ing substance,  because  it  renders  the  microbe  sensitive  to  the  action 
of  normal  serum ;  also  an  immunizing  substance  or  mediator,  sensi- 
tizer, amboceptor,  intermediary  body,  because  it  exists  in  the  serum 
of  animals  immunized  against  the  microbe.  The  common  substance 
contained  in  the  normal  serum  has  been  called  a  thermolabile  sub- 
stance, because  it  is  destroyed  at  60°  C. ;  and  because  it  completes 
the  action  of  immunizing,  it  is  known  as  a  complementary  substance, 
complement,  or  alexine,  or  cytase. 

We  have  seen,  in  injecting  an  animal  a  of  species  A,  that  the  red 
blood-corpuscles  coming  from  the  animal  of  another  species,  B,  will 
cause  a  specific  agglutinin  to  appear  in  the  serum  of  the  animal 
injected,  a.  But  there  appears  at  the  same  time  also  a  hsemolysin. 
After  having  agglutinated  the  red  corpuscles  of  an  animal  of  the 
species  B.  the  serum  of  the  animal  a  dissolves  them,  or,  to  speak 
more  exactly,  breaks  the  union  of  their  stroma  with  their  hsBmo- 
globin,  and  the  latter  passes  in  solution  into  the  surrounding  fluid. 
It  has  been  shown  that  hsemolysin  is  specific  and  does  not  act  except 
on  the  red  corpuscles  of  the  species  B^.  which  has  served  for  the  pre- 
paratory injections.  It  has  been  found  that  hgemolysis,  like  bac- 
teriolysis, is  accomplished  in  two  periods  of  time ;  that  the  haemolysins. 
like  the  bacteriolysins,  are  formed  of  two  substances :  an  intermediary 
body  or  amboceptor,  and  a  complement  or  alexin.  The  specific  sub- 
stance is  amboceptor,  the  alexin  is  the  same  common  complement  or 


296  PHYSIOLOGY. 

alexin  which  acts  upon  the  various  sensitized  bacteria.  Take  an  illus- 
tration in  which  the  characters  are  reversed.  We  may  regard  the 
pepsin  in  artificial  digestion  as  the  amboceptor,  and  the  acid  as  the 
complement.  The  pepsin  or  amboceptor  occurs  only  in  immune  serum, 
while  the  acid,  which  may  be  hydrochloric  or  phosphoric,  corresponds 
to  the  complement  found  in  a  variety  of  serums.  The  lock  and  key 
simile  of  E.  Fischer  affords  perhaps  the  best  analogy.  The  lock  is 
the  cell,  the  key  is  the  amboceptor,  and  the  hand  which  turns  the  key 
is  the  complement.  The  blood  of  vertebrates  contains  two  kinds  of 
bodies,  which  Metchnikoff  designates  as  macrophages  or  large  mono- 
nuclear leucocytes,  and  the  smaller  polymorphous,  nuclear  white  cells 
or  microphages.  The  macrophages  attack  the  xanthocytes,  or  large 
animal  cells,  and  malarial  parasites.  The  microphages  prefer  the 
bacteria  of  acute  diseases.  The  complement  occurs  in  normal  animals 
the  amboceptor  is  developed. 

Haemolysins  are  derived  from  the  leucocytes.  Bacteriolysins 
are  contained  in  the  euglobulin  fraction  of  the  serum. 

Enterokinase  acts  like  an  amboceptor,  uniting  the  red  corpuscles 
of  the  blood  to  trypsinogen,  which  behaves  like  a  complement  and 
dissolves  the  red  blood-corpuscles. 

The  toxic  action  of  cobra-poison  upon  red  blood-corpuscles 
depends  upon  the  combination  of  amboceptors,  intermediary  l)odies 
contained  in  the  venom,  with  corresponding  complements  contained, 
not  in  the  venom,  but  in  the  cells  or  fluids  of  the  animal  acted  upon. 
Kyes,  working  with  cobra-vemon.  found  an  endo  complement  con- 
tained in  the  red  corpuscles  themselves.  Kyes  also  found  that 
lecithin  is  capable  of  combining  with  venom  intermediary  and  thus 
completing  the  hsemolytic  potency  of  venom.  Here  is  a  cytotoxin 
formed  of  an  intermediary  body  and  a  definite  crystallizable  sub- 
stance uniting  with  it,  thus  acting  as  a  complement.  Here  we  have 
a  poison  in  our  own  body,  only  needing  the  intermediary  body  of  the 
venom  to  act  upon  us.  Snake-poison  only  contains  one-half  of  the 
complete  poison.  Eattlesnake-poison  has  been  found  by  Flexner  and 
Noguchi  also  to  contain  another  cytotoxin  which  has  the  power  to 
dissolve  endothelial  cells,  an  endotheliallysin. 

According  to  Metchnikoff,  the  complement,  or  cytase,  comes 
from  the  leucocytes  when  the}''  are  damaged.  It  is  an  important 
function  of  the  mother  to  transfer  to  the  suckling,  through  her  milk, 
immunizing  bodies,  and  the  infant's  stomach  has  the  capacity,  which 
is  afterwards  lost,  of  absorbing  these  substances  in  the  active  state. 
The  relative  richness  of  the  suckling's  blood  in  protective  antibodies. 


THE  CIRCULATION.  297 

as  contrasted  with  the  artifieally  fed   infant,   explains  the  greater 
freedom  of  the  former  from  infectious  disease. 

OPSONINS. 

There  is  in  normal  serum  a  substance  which  so  acts  upon  bac- 
teria as  to  render  them  susceptible  of  being  devoured  by  the  leuco- 
cytes. In  some  way  serum  stimulates  phagocytosis  by  making  the 
bacteria  more  susceptible  of  being  absorbed  by  leucocytes.  This  sub- 
stance in  the  serum  has  been  denominated  by  Wright  and  Douglass, 
opsonin  (feast-preparer). 


CHAPTER  VII. 

RESPIRATION. 

The  study  of  digestion  and  circulation  has  taught  the  reader  the 
nature  of  the  methods  and  the  avenues  along  which  ingested  mate- 
rials must  pass  in  the  processes  of  their  elaboration  in  order  to  main- 
tain the  requirements  of  life.  It  has  also  made  him  acquainted  with 
the  various  forms  under  which  those  materials  became  absorbable  and 
miscible  with  the  blood,  and  which  must  necessarily  be  renewed  in 
proportion  as  the  latter  is  changed  by  the  nutrient  movement.  It  is 
known,  too,  that  the  liquid  and  soluble  products  of  digestion  and  the 
lymph  itself,  when  poured  into  the  venous  blood,  do  not  have  the  qual- 
ities of  a  directly  nutrient  fluid  immediately  after  their  mixture 
with  the  blood.  In  order  that  these  qualities  should  develop  it  is 
necessary  that  there  should  occur  the  intervention  of  an  essential  ele- 
ment, which  animals  find  in,  and  incessantly  draw  from,  the  envelop- 
ing atmosphere — oxygen.  The  latter  is  the  great  agent  in  the  final 
transformations  which  the  various  organic  matters  must  undergo. 
The  introduction  of  a  certain  proportion  of  oxygen  into  the  economy 
is,  therefore,  the  first  aim  of  the  function  of  respiration. 

The  general  tendency  of  the  various  gases  to  mingle  even  when 
wet  membranes  separate  them  has  been  pointed  out.  Looked  at  in 
its  essential  character,  the  respiration  of  animals  consists  in  a  single 
exchange  of  gases  which  takes  place  during  the  action  exercised  by 
the  air  upon  the  blood.  In  fact,  atmospheric  oxygen,  brought  into 
contact  with  a  thin,  membranous  wall,  passes  through  it  and  pene- 
trates the  blood,  while  the  carbonic-acid  gas  contained  in  that  liquid 
is  freed  from  it  through  the  same  membrane.  Therefore,  if  respira- 
tion, on  the  one  hand,  takes  something  away  from  the  blood,  on  the 
other,  it  communicates  to  it  a  principle  which  renders  it  suitable  to 
complete  the  organs,  furnish  material  for  their  secretions,  or  to  repair 
their  losses,  while,  at  the  same  time,  it  gives  rise  to  a  disengage- 
ment of  heat  indispensable  to  the  free  exercise  of  the  functions.  It 
is  this  vivifying  principle  which  combines  with  the  organic  matters 
of  the  blood  to  form  the  water  and  carbonic  acid  that  are  unceas- 
ingly eliminated  by  expiration  and  which  are  soon  decomposed  in 
the  atmosphere  under  the  influence  of  solar  radiation,  to  furnish  car- 
bon and  hydrogen  to  vegetation. 
(298) 


RESPIRATION.  299 

The  blood,  with  its  complex  constitution,  becomes  in  this  way 
the  principal  medium  for  all  the  phenomena  of  nutrition.  It  is 
known  to  be  collecting,  in  its  course,  for  its  own  reconstitution,  cer- 
tain materials  elaborated  by  the  digestive  passages  and  then  deposit- 
ing assimilable  principles  in  the  various  tissues.  The  blood  repre- 
sents, therefore,  a  reparatory  fluid  whose  continual  renewal  and 
destruction,  intrusted  to  digestion  and  respiration,  constitute  the  two 
inseparable  conditions  for  existence  of  the  higher  animals. 

When  air  is  fed  to  the  wood  in  the  firebox  of  a  boiler  a  process 
known  as  burning  takes  place.  It  is  a  real  chemical  process:  the 
oxygen  unites  with  the  carbon  and  hydrogen  of  the  wood,  so  that 
both  the  wood  and  oxygen  disappear  as  such.  The  carbon  and  a  por- 
tion of  the  oxygen  unite  to  form  carhonic-acid  gas.  The  hydrogen 
and  the  remainder  of  the  oxygen  by  their  union  form  water.  The 
two  substances  thus  formed  pass  off  in  the  smoke,  leaving  behind  as 
the  debris,  or  ashes,  the  mineral  part  of  the  wood.  By  this  burning, 
also  termed  oxidation,  heat  and  a  flame  are  produced. 

Within  the  body  there  occurs  an  analogous  process,  also  termed 
oxidation,  whereby  the  oxygen  inhaled  into  the  body  slowly  burns  the 
protoplasm  of  cells  in  a  manner  similar  to  the  burning  of  the  wood  in 
the  boiler.  This  process  within  the  body  is  performed  so  slowly  that 
there  is  no  appearance  of  a  flame,  but  there  is  yielded  the  same 
amount  of  heat  as  would  be  produced  were  the  same  materials  burned 
within  a  furnace  or  stove.  Some  of  this  heat  is  utilized  to  give 
warmth  to  the  body,  while  the  remainder  of  it  is  converted  into 
power  and  energy,  so  that  the  body  may  do  work,  either  of  motion, 
thought,  or  manufacturing  the  various  products  of  the  body.  Oxida- 
tion is  the  essential  process  of  life;  when  it  ceases,  life  ends.  It 
occurs  in  every  cell  of  the  economy.  Its  degrees  in  the  living 
cells  can  be  heightened  or  lowered  according  to  the  needs  of  the 
body.  The  end-products  of  body-oxidation  are  also  carbonic-acid 
gas,  water,  and  ashes,  or  urea  as  occurred  in  furnace  oxidation. 

From  studies  in  general  physiology  it  is  known  that  the  peculiar 
form  of  energy  which  is  called  life  exists  only  in  association  with 
living  cells  or  living  organisms.  It  is  liberated  only  during  a  catab- 
olism,  or  destructive  metabolism  of  living  cell-protoplasm,  and  this 
metabolism  is  possible  only  in  the  presence  of  oxygen.  During  these 
catabolic  metabolisms  the  living  protoplasm  of  the  cell,  the  deeply 
complex  protoplastic  molecule,  is  split  up  into  two,  perhaps  more, 
simpler  molecules;  these  last,  which  probably  represent  proteids, 
may  again  separate  into  still  simpler  ones.     Each  change  from  a 


300  PHYSIOLOGY. 

complex  compoimd  to  a  simpler  one  leads  to  (1)  liberation  of  energy 
upon  which  depend  the  numerous  activities  of  life  and  (2)  to  a  new 
combination  of  the  simpler  molecules  with  oxygen.  Thus,  oxygen 
is  the  cause  of  combustion,  and  the  complement  of  cataholism. 

Respiration  is  the  general  term  that  includes  all  of  those  activ- 
ities that  are  involved  in  the  furnishing  of  oxygen  to  the  tissues  and 
the  removal  of  CO2  from  the  tissues  of  a  living  organism. 

The  respiratory  phenomena  do  not  exist  in  man  and  the  aerial 
vertebrates  only.  They  are  found,  of  the  most  varied  kinds,  in  all  of 
the  animal  species,  even  in  the  lowest;  these  last,  lacking  true  blood 
as  well  as  a  digestive  tube,  have  particular  juices  introduced  by  ab- 
sorption, the  nutritive  quality  of  which  can  develop  only  under  the 
vivifying  influence  of  atmospheric  oxygen.  It  may  here  be  added 
that  the  intervention  of  this  gas  is  as  indispensable  to  the  plant  as  to 
the  animal  in  all  periods  of  life.  The  sap,  analogous  to  the  blood, 
cannot  be  sufficiently  elaborated  and  become  a  really  nourishing 
fluid  except  by  the  oxygen. 

When  a  function  is  found  in  all  living  beings,  it  is  logical  to 
conclude  that  it  represents  one  of  the  fundamental  conditions  of 
their  existence.  Respiration  incontestably  offers  that  character. 
Not  only  do  all  living  species  breathe  at  their  different  ages,  but  they 
cannot  develop,  or  persist  in  their  development,  except  by  the  accom- 
plishment of  that  function.  The  most  positive  experiments  have 
demonstrated  that  the  cell  of  the  plant  and  the  cell  of  the  animal 
breathe,  one  in  the  seed  and  the  other  in  the  egg  in  which  it  is  organ- 
ized, and  that  all  development  is  arrested  as  soon  as  communication 
with  the  atmospheric  air  is  prohibited.  The  seed  absorbs  oxygen 
from  the  air  for  the  benefit  of  the  young  plant  that  it  contains,  fixes 
some  traces  of  nitrogen,  and  at  the  same  time  exhales  a  considerable 
quantity  of  carbonic  acid. 

It  was  in  a  chicken's  egg  that  respiration  of  the  embryo  was  first 
recognized;  when  the  surface  of  the  egg  was  covered  with  an  im- 
pervious coating  of  oil  or  varnish,  the  embryo  failed  to  develop. 
Later  it  was  proved  that  the  egg  containing  a  chick  in  the  process 
of  development  also  absorbs  oxygen  and  exhales  carbonic  acid. 

The  life  of  mammals  shows  another  form  of  the  phenomenon: 
in  them  the  foetus,  by  reason  of  a  certain  union  of  its  vascular  appa- 
ratuses, draws  from  the  blood  of  the  mother  the  necessary  oxygen 
which  its  pulmonary  surface  cannot  yet  supply.  The  villi  of  the 
placenta,  plunged  into  the  vascular  sinuses  of  the  uterus,  effect 
a  kind  of  respiration  there. 


RESPIRATION.  301 

THE  RESPIRATORY  APPARATUS. 

The  object  of  respiration  is  twofold,  viz. :  to  supply  the  oxygen 
necessary  for  the  numerous  oxidation  processes  that  are  constantly 
occurring  within  the  body,  as  well  as  to  remove  the  carhon  dioxide 
formed  within  the  body.  The  most  important  organs  for  this  pur- 
pose are  the  lungs  or  the  gills,  as  the  case  may  be,  though  it  must 
never  be  entertained  for  a  moment  that  they  are  the  special  seats  for 
those  combustion-processes  whereby  ensues  carbonic  acid  as  the  final 
result.  These  processes  occur  in  all  parts  of  the  body  in  the  sub- 
stance of  the  tissues.  The  lungs  or  the  gills  are  merely  the  medium 
for  the  exchange  of  the  two  essential  gases.  For  this  interchange  it 
becomes  necessary  that  the  atmospheric  air  should  pass  into  them  and 
that  the  changed  air  should  be  expelled  from  them. 

In  essence  a  lung  or  a  gill  is  constructed  of  a  thin  membrane, 
whose  one  surface  is  exposed  to  the  air  or  water, — depending  upon 
the  species  of  animal, — while  on  the  other  surface  there  is  a  network 
of  blood-vessels,  the  separating  membrane  between  the  blood  and 
aerating  medium  being  the  thin  walls  of  the  small  blood-vessels  and 
the  fine  membrane  upon  which  they  are  distributed.  The  principle 
is  always  the  same  in  all  respiratory  apparatuses;  the  difference 
between  the  simplest  and  most  complicated  ones  is  one  of  degree 
only. 

In  all  animals  in  which,  by  reason  of  their  complex  structure,  it 
becomes  necessary  to  have  special  arrangements  for  the  performance 
of  the  respiratory  function  it  is  found  that  the  act  is  divided  into 
two  stages:  (a)  an  external  respiration,  where  the  interchange  is 
between  the  air  or  water  on  the  one  hand,  and  the  circulating 
medium  of  blood  on  the  other,  as  it  passes  through  richly  vascu- 
lar skin,  tracheEB,  gills  or  lungs;  (&)  an  internal  respiration,  which 
is  an  interchange  between  the  blood  or  the  lymph  and  the  cells  of  the 
various  tissues  of  the  entire  body. 

Our  consideration  of  the  subject  will  confine  us  to  the  study  of 
the  human  respiratory  organs.  The  most  important  of  the  human 
apparatus  are  the  lungs,  which  are  contained  within  the  closed  chest, 
or  thorax,  and  have  no  communication  with  the  outside  except 
through  the  avenue  of  the  respiratory  passages. 

The  pulmonary  apparatus  consists  of:  (1)  the  air-passages — 
nose,  pharynx,  larynx,  trachea,  and  the  bronchi,  which  communicate 
with  the  lungs;  (2)  the  lungs  with  their  immense  number  of  small 
sacs,  known  as  the  air-vesicles;    and  (3)  the  thorax.     The  accessory 


302 


PHYSIOLOGY. 


nmscles  of  respiration,  when  called  into  play,  make  the  thorax  act 
as  a  bellows,  forcibly  causing  ingress  and  egress  of  air. 

The  Air-passages. — The  very  first  portion  of  the  respiratory  pas- 
sageway, the  nose,  is  the  organ  of  the  special  sense  of  smell  and  will 
be  treated  in  detail  when  that  subject  is  discussed;  the  anatomy  of 
the  pharynx  has  been  previously  noted  when  the  alimentary  canal  was 
under  attention.  The  larynx  is  placed  at  the  upper  part  of  the  pas- 
sage, being  a  dilatation  of  the  trachea.  It  is  the  cartilaginous  box 
which  contains  the  structures  concerned  in  the  production  of  voice. 
It  will  be  described  later  in  connection  with  that  function. 


Fig.  111. — Human  Respiratory  Apparatus.      (Duval.) 
It  shows  the  branching  of  the  bronchia  in  the  interior  of  the  lungs. 

The  Trachea  and  Bronchi. — The  trachea,  or  windpipe,  is  a  com- 
bined membranous  and  cartilaginous  cylindrical  tube,  flattened  pos- 
teriorly. Commencing  opposite  the  fifth  cervical  vertebra,  it  ter- 
minates by  dividing  into  two  bronchi  opposite  the  third  dorsal  ver- 
tebra. Its  length  is  about  four  inches,  its  breadth  (less  in  the  female 
than  in  the  male),  three-fourths  of  an  inch.  The  bronchi  diverge 
from  the  trachea  to  the  lungs  behind  the  great  blood-vessels  running 


RESPIRATION. 


303 


from  the  base  of  the  cardiac  organ.  The  bronchus  on  the  right  side, 
about  an  inch  in  length,  runs  at  a  right  angle  to  the  root  of  the 
lung  on  a  level  with  the  fourth  dorsal  vertebra  and  posterior  to  the 
right  pulmonary  artery.  The  left  bronchus,  less  in  diameter  than 
the  right,  but  about  twice  its  length,  passes  downward  and  outward 
beneath  the  arch  of  the  aorta  to  the  root  of  its  corresponding  lung. 
The  bronchi  and  the  trachea  are  composed  of  a  series  of  cartilaginous 
rings  lined  with  mucous  membrane.  The  trachea  and  bronchi  are 
encircled  by  the  cartilaginous  rings,  which  are  not  closed  posteriorly 


Fig.  112. — Bronchia  and  Lungs,  Posterior  View.  (Sappey.)  (From 
Mills's  "Animal  Physiolog3',"  copyright,  1889,  by  D.  Appleton  and 
Company. ) 

1,  1,  Summit  of  lungs.  2,  2,  Base  of  lungs.  3,  Trachea.  4,  Right  bron- 
chus. 5,  Division  to  upper  lobe  of  lung.  6,  Division  to  lower  lobe.  7,  Left 
bronchus.  8,  Division  to  upper  lobe.  9,  Division  to  lower  lobe.  10,  Left  branch 
of  pulmonary  artery.  11,  Right  branch.  12,  Left  auricle  of  heart.  13,  Left 
superior  pulmonary  vein.  14,  Left  inferior  pulmonary  vein.  15,  Right  superior 
pulmonary  vein.  16,  Right  inferior  pulmonary  vein.  17,  Inferior  vena  cava. 
18,    Left   ventricle   of   heart.      19,    Right   ventricle. 


except  by  a  strong  fibro-elastic  membrane,  and  contain  a  layer  of  pale 
unstriped  muscular  fibers  running  in  a  transverse  and  longitudinal 
direction.  The  cartilaginous  rings  preserve  the  caliber  of  the  trachea. 
The  brachial  mucous  membrane  is  smooth  and  its  color  is  reddish 


304  PHYSIOLOGY. 

white.  Its  epithelium  is  of  the  ciliated  columnar  form.  The  vibra- 
tory movement  of  tlie  cilia — being  directed  upward — removes  dust 
from  the  lungs.  Minute  glands  of  the  racemose  variety,  which  open 
upon  the  surface,  are  found  in  the  trachea  and  bronchi.  The  nerves 
supplying  the  trachea  and  lungs  are  the  pneumogastric  and  the 
sympathetic. 

The  Lungs  are  in  the  thorax,  one  on  each  side,  separated  by  the 
heart  and  the  large  blood-vessels.  In  the  constantly  changing 
diameters  of  the  chest  they  accurately  fill  the  chest  which  contains 
them.  They  are  free,  and  attached  only  by  their  roots.  They  are 
closely  invested  with  a  serous  membrane,  the  pleura.  The  root  of 
the  lung  is  placed  near  its  middle  internally,  and  consists  of  the 
bronchus,  the  pulmonary  arteries  and  the  veins,  the  blood-vessels  of 
the  bronchia,  nerves,  and  lymphatics,  all  invested  with  a  reflection 
of  pleura.  The  right  lung  has  its  root  behind  the  superior  vena 
cava.  The  root  of  the  left  lung  lies  partly  beneath  the  arch  of  and 
partly  in  front  of  the  descending  portion  of  the  aorta.  In  the  root 
of  the  right  lung  the  bronchus  is  the  highest;  in  the  root  of  the 
left  lung  the  pulmonary  artery  is  the  highest.  The  bronchi,  before 
entering  a  depression  at  the  root  of  the  lungs,  the  hilus,  subdivide, 
the  right  into  three  branches,  the  left  into  two,  corresponding  to  the 
number  of  lobes  in  each  lung.  Each  lung  is  conical,  with  a  broad, 
concave  crest  resting  on  the  diaphragm  and  a  rounded  apex  standing 
above  the  level  of  the  first  rib  into  the  neck.  Its  outer  surface  is 
convex  and  its  inner  surface  is  concave  and  faces  the  heart. 

The  weight  and  the  capacity  of  the  lungs  vary  according  to 
many  conditions.  Their  average  weight  is  about  two  and  one-half 
pounds  and  their  total  capacity  three  hundred  cubic  inches.  Their 
long  diameter  is  the  greatest  and  deepest  on  the  posterior  surface. 
The  right  lung  is  shorter  than  the  left,  but  wider  and  of  somewhat 
greater  bulk.  The  right  lung  has  three  lobes,  of  which  the  middle 
one  is  the  smallest  and  the  lowest  one  the  largest.  The  left  lung 
has  two  lobes,  of  which  the  lower  is  the  larger.  Between  the  lobes 
of  the  left  lung  in  front  there  exists  a  large  angular  notch,  corres- 
ponding with  the  position  at  which  the  impulse  of  the  heart  is  felt 
against  the  walls  of  the  chest. 

Normal  lung-tissue  always  shows  a  specific  gravity  less  than  that 
of  water;  consequently  it  will  float  when' thrown  into  water.  No 
other  tissue  does  this.  However,  should  lung-tissue  in  which  con- 
solidation has  resulted  from  some  disease  or'  the  lung-tissue  from  a 
child  that  has  never,  breathed  be  thus  tried,  it  will  sink  like  other 


RESPIRATION.  305 

tissues.  This  water-test  of  the  lungs  is  one  of  the  medico-legal  tests 
applied  to  ascertain  whether  a  child  found  dead  was  "stillborn"  or 
was  a  victim  of  infanticide. 

The  substance  of  the  lung  is  of  a  light,  porous,  spongy  texture, 
when  handled  crepitating  because  of  the  air  contained  in  its  tissue. 
Lung-tissue  is  very  highly  elastic;  it  completely  collapses  when  re- 
moved from  the  thorax  or  if  the  thoracic  walls  be  punctured  so  as  to 
admit  air  from  the  outside  into  the  pleural  cavity. 


Fig.  113. — ]\IolcI  of  n,  Terminal  Bronchus  and  a  Group  of  Air-cells 
Moderately  Distended  by  Injection,  from  the  Human  Subject.  (Robin.) 
(From  ilills's  "Animal  Physiologj',"  copyright,  1889,  by  D.  Appleton 
and  Company.) 

In  color  the  lungs  are  pinkish  at  birth,  but  of  a  mottled  slate 
color  in  adult  life.  The  dark-colored  patches  are  produced  by  the 
presence  of  carbonaceous  material  that  has  been  inhaled  and  deposited 
within  the  areolar  tissue  near  the  surface  of  the  organ.  The  carbon 
particles  are  absorbed  ])y  the  lymphatics,  being  carried  into  the  lym- 
phatic openings  by  the  leucocytes. 

Bronchi. — In  structure  the  bronchi  resemble  the  trachea.  In  the 
bronchi,  however,  there  are  unstriped  muscular '  fibers  forming  the 

20 


306  PHYSIOLOGY. 

muscularis  mucosce,  while  the  cartihigiiious  elements  arc  scattered 
about  equally  in  all  parts  of  their  circumference. 

As  the  bronchi  are  traced  in  the  lungs  they  divide  into  tubes  of 
less  diameter.  These  again  subdivide  into  tubes  growing  smaller  in 
a  gradual  manner.  After  a  certain  stage  of  division  each  tube  is 
reduced  to  a  size  about  one-fiftieth  of  an  inch,  and  is  denominated 
a  bronchiole,  and  its  walls  are  lined  with  small  hemispherical  saccules 
called  alveoli,  or  air-cells.  These  bronchioles  then  open  into  blind 
spaces  called  infundibula,  which  are  lined  with  air-cells.  Near  the 
ending  of  the  bronchiole  with  the  infundibulum  the  former  ciliated 
epithelium  disappears  and  another  variety  of  epithelium  appears. 
This  new  variety  of  epithelium   consists  of  small,   flat,   pol3'gonal 


Fig.  114. — Termination  of  a  Bronchus  in  an  Alveolus. 
a,  Bronchiole.    6,  Cavity  of  the  alveolus,    c.  Air-cells. 

nucleated  cells.     This  flat,  thin  epithelium  also  lies  over  the  blood- 
vessels and  even  extends  between  the  blood-vessels. 

The  alveoli  of  any  group  or  series  always  communicate  with  one 
another  to  open  by  a  common  orifice  into  a  terminal  bronchus.  In 
size  they  average  roughly  one  one-hundredth  of  an  inch  in  diameter. 
Form  is  given  to  the  air-cells  by  the  presence  of  a  fine  membrane  of 
slightly  fibrillated  connective  tissue  which  contains  some  corpuscles. 
This  is  closely  surrounded  by  a  great  many  fine,  elastic  fibers  which 
give  to  the  pulmonary  parenchyma  its  characteristic  elasticity. 
Some  nonstriped  muscular  fibers  are  apparent  in  the  connective 
tissue  between  the  cells;  in  certain  diseases  these  become  abnormally 
developed.  The  number  of  alveoli  has  been  estimated  to  be  seven 
hundred  and  twenty-five  millions,  whose  superficial  area  is  one  hun- 
dred times  greater  than  that  of  the  body. 


RESPIRATION. 


307 


Within  the  alveolar  walls  exists  a  dense  capillary  network. 
They  are  placed  more  toward  the  inner  side  of  the  vesicle,  being- 
covered  only  by  the  thin  lining  of  the  air-sacs.  So  densely  are  they 
arranged  that  the  spaces  between  the  capillaries  are  even  narrower 
than  the  diameter  of  the  capillaries,  which  here  are  about  one  three- 
thousandth  of  an  inch  in  diameter.  In  man  between  the  folds  of 
two  adjacent  air-cells  there  is  found  but  a  single  layer  of  capillaries, 
while  on  the  boundary  line  between  two  air-cells  the  course  of  the 
capillaries  becomes  so  twisted  that  they  project  into  the  cavities  of 


Fig.  115. — fcjection  of  the  Pareiiehyuia  of  tiie  Human  Lung,  Injected 
Through  the  Pulmonary  Artery.  (Schulze.)  (From  Mills's  "Animal 
Physiology,"  copyright,   1889,  by  D.  Appleton  and  Company.) 

a,  a,   c,  c.  Walls  of  the  air-ceUs.     6,  Small  arterial  branch. 


the  alveoli.  By  these  arrangements,  and  particularly  since  the  inter- 
vening septa  are  so  very  thin  and  permeable,  the  exposure  of  the 
blood  to  the  air  becomes  complete,  as  two  sides  of  a  capillary  are 
thus  exposed  at  the  same  time. 

Blood-supply. — The  lungs  receive  a  copious  supply  of  blood  from 
two  sources :  (1)  the  pulmonary  and  (2)  the  bronchial  arteries.  The 
bronchial  arteries  furnish  nutriment  for  the  lung-tissues.  Six  thou- 
sand liters  of  blood  pass  through  the  lungs  in  twenty-four  hours. 


308  PHYSIOLOGY. 

The  Pleura. — Each  lung  is  enveloped  by  a  serous  membrane — 
the  pleura — composed  oi  two  layers,  one  of  which  is  closely  adherent 
to  the  external  surface  of  the  lung;  the  other  adheres  to  the  inner 
surface  of  the  chest-wall.  These  layers  are  designated  visceral  and 
parietal.  The  visceral  pleura  envelops  the  lung,  while  the  parietal 
pleura  lines  the  thoracic  wall.  The  two  become  continuous  with  one 
another  at  the  root  of  the  lung. 

By  this  means  two  large  serous  sacs  are  formed,  each  distinct 
and  separate  from  the  other.  The  pleural  tissue  is  composed  of  a 
layer  of  fibrous  tissue  covered  with  endothelium.  During  health  the 
two  layers  of  the  pleura  are  always  in  contact  with  one  another,  just 
enough  fluid  l)eing  present  between  them  to  allow  of  their  gliding 
over  one  another  with  but  very  little  friction  during  the  accomplish- 
ment of  the  respiratory  acts. 

Lymphatics. — These  are  very  numerous  in  lung-tissue  and  so 
arranged  as  to  form  several  systems. 

Nerves. — The  nervous  supply  of  the  lungs  is  from  the  anterior 
and  posterior  puhnonary  plexuses  derived  from  the  vagus  and  sympa- 
tlietic.  The  nerves  enter  the  lungs  to  follow  the  course  of  the 
bronchi  and  their  branches  and  end  in  the  unstriped  muscle. 

The  function  of  the  nonstriped  muscular  tissue  of  the  lungs 
seems  to  be  to  offer  a  general  resistance  to  increased  pressure  within 
the  air-passages  as  may  occur  during  forced  expiration,  as  speaking, 
singing,  blowing,  etc.  The  vagus  is  the  nerve  which  supplies  motor 
fibers  to  these  muscle-fibers. 

MECHANISM   OF  RESPIRATION. 

If  respiration  be  suspended  for  but  a  very  short  while,  soon 
there  will  be  felt  a  lively  anxiety  due  to  the  nonsatisfaction  of  an 
imperative  need.  This  sensation  of  anxiety  is  produced  by  an  inter- 
nal sensation  calling  for  need  of  breathing,  it  being  promptly  relieved 
by  the  proper  introduction  of  air  into  the  lungs.  When  the  air 
inspired  and  retained  becomes  unfit  for  further  oxidation,  there 
arises  another  internal  sensation  which  calls  for  the  expulsion  of 
that  same  air.  Each  respiratory  movement  is,  therefore,  preceded 
by  a  particular  sensation  which  commands  its  execution. 

These  two  movements  constitute,  by  their  regular  succession,  a 
complete  respiration,  the  purpose  of  which  is  to  maintain  in  the  lungs 
regular  currents  which  serve  incessantly  to  renew  the  air  altered  by 
its  contact  with  the  blood.  The  mechanism  for  the  accomplishment 
of  respiration  consists  in  an  alternate  dilatation  and  contraction  of 


RESPIRATION.  309 

the  chest  by  means  of  which  air  is  drawn  into  or  expelled  from  the 
lungs.  These  two  acts  have  received  the  respective  names:  inspira- 
tion and  expiration.  x4s  is  known,  the  whole  external  surfaces  of 
the  lungs  are  in  direct  contact  in  an  air-tight  manner  with  the  inner 
wall  of  the  thorax,  so  that  the  lungs  must  be  distended  with  every 
dilatation  of  the  thoracic  wall  as  well  as  be  diminished  in  volume  by 
every  contraction  of  the  same  wall.  The  movements  of  the  lungs 
are,  therefore,  for  the  most  part,  passive,  being  dependent  upon  the 
movements  of  the  thoracic  wall.  This  close  approximation  of  lung 
to  thoracic  wall  is  dependent  upon  a  state  of  elastic  tension  main- 
tained within  the  lung,  due  to  pressure  exerted  by  the  presence  in 
the  lunff  of  residual  air. 


Fig.  116. — Diagrammatic  Represontation  of  the  Action  of  the 
Diaphragm.      (Beclard.  ) 

If  a  represents  a  plane  extending  in  expiration  from  the  sternum  to  the 
vertebra,  and  D  the  position  of  the  diaphragm  in  inspiration,  the  plane  a  will 
move  to  A,   while  the   diaphragm   will   descend   to   (/. 

From  these  data  it  becomes  evident  that  all  that  is  necessary 
for  the  production  of  inspiration  is  such  a  movement  of  the  walls 
or  the  diaphragm,  or  the  movement  of  the  two  synchronously,  that 
the  capacity  of  the  interior  should  be  increased.  By  reason  of  this 
increase  there  would  be  produced  a  temporary  vacuum  in  the  newly 
acquired  space,  or  at  least  a  great  diminution  of  pressure  within  the 
lungs,  so  tha't  atmospheric  pressure  upon  the  outside  is  greater  than 
that  within.  Consequently  there  will  be  generated  a  current  of  air 
proceeding  from  the  outside  air  through  the  larynx  and  trachea  into 
the  lungs,  for  the  purpose  of  equalizing  the  pressure  upon  the  inside 
and  outside  of  the  chest.  The  moment  this  point  is  reached  there 
is  cessation  of  the  current.  This  incoming  of  the  air  constitutes  the 
first  of  the  two  acts  of  respiration,  namely:    inspiration. 

For  the  expulsion  of  the  air  that  is  no  longer  fit  for  oxidation 


310 


PHYSIOLOGY. 


it  is  evident  that  there  must  be  a  reverse  movement  of  the  thoracic 
walls  whereby  the  chest-capacity  is  diminished.  This  act  increases 
the  pressure  exerted  by  the  contained  air,  with  the  result  that  as 
much  of  it  is  expelled  along  the  usual  avenues  for  its  passage  as  is 
necessary  to  equalize  the  pressure  upon  the  inside  and  outside  of 
the  chest.  This  outgoing  of  air  constitutes  the  second  act  of  respira- 
tion: expiration.  The  regular  succession  of  these  two  alternating 
currents  of  air  constitutes  breathing,  or  respiration. 


Fig.  117. — The  Action  of  the  Ribs  in  Man  in  Inspiration.      (Beclabd.) 

The  shaded  parts  represent  the  positions  of  the  ribs  in  repose.  The  line 
A-B  represents  a  horizontal  plane  passing  through  the  sternal  extremity  of 
the  seventh  rib;  the  line  C-D  represents  a  horizontal  plane  touching  the 
superior  extremity  of  the  sternum;  the  line  H-G  indicates  the  linear  direction 
of  the  sternum.  When  the  ribs  are  elevated  as  indicated  by  the  dotted  lines, 
the  line  A-B  becomes  the  plane  a-b,  the  line  C-D,  the  line  c-d,  and  the  line 
H-G  becomes  the  line  h-g,  the  projection  of  the  sternum  being  more  marked 
interiorly.  The  distance  which  separates  the  line  M-N  from  the  line  m-n 
measures  the  increase  in  the  antero-posterior  diameter  of  the  thorax. 


Inspiration. — Inspiration  has  for  its  motive  agents  the  dia- 
phragm, the  scaleni,  the  external  intercostals,  the  stemo-cleido-mas- 
toid,  the  angularis  scapulae,  the  small  pectoral,  the  serratus  magnus, 


RESPIRATION. 


311 


and  the  trapezius  fibers,  with  the  great  pectoral.  All  of  these  mus- 
cles by  their  contraction  directly  affect  the  expansion  of  the  chest, 
with  the  exception  of  the  angularis  scapula  and  trapezius,  whose 
action  is  indirect.  The  diaphragm  is,  par  excellence,  the  muscle  of 
inspiration;  the  others  do  not  contract  very  extensively  except  for 
the  needs  of  labored  or  forced  inspiration.  The  scaleni  are  concerned 
in  women  to  aid  inspiration  of  the  superior  costal  type,  which  is 
peculiar  to  the  sex. 


118. — ychema  of  Rt'.s])iratury  Mecluuiisni  in  Inspiiutiou. 
(Laulanie.)      (See  explanation.  Fig.   119.) 

When  a  person  is  devoid  of  strong  emotions  or  is  not  engaged 
in  work  or  exercise,  the  breathing  is  quiet  and  regular.  It  is  then 
said  to  be  of  the  ordinary  type  and  is  principally  diaphragmatic  in 
character. 

When,  however,  the  breathing  is  extraordinary  in  type,  various 
other  muscles  are  called  into  action. 

The  size  of  the  chest-cavity  is  increased  in  (a)  its  vertical 
diameter  as  well  as  in  (&)  its  lateral  and  antero-posterior  diameters. 
The  diameters  are  ascertained  by  means  of  calipers. 

From  the  student's  study  of  anatomy  he  knows  that  the  dia- 
phragm, when  at  rest  and  in  a  state  of  relaxation,  presents  the  gen- 


312 


PHYSIOLOGY. 


eral  form  of  a  dome.  The  peak,  or  convexity,  of  the  dome  points 
upward.  The  student  also  knows  that  during  contraction  all  mus- 
cles shorten  their  fibers,  to  which  law  the  diaphragm  is  no  exception. 
By  its  contraction  the  convexity  of  the  dome  is  materially  dimin- 
ished, thereby  producing  more  space  and  increasing  the  vertical  diam- 
eter. This  helps  very  materially  to  produce  a  vacuum  into  which  air 
from  outside  of  the  body  is  pushed  ])y  atmospheric  pressure.  That 
is,  there  occurs  inspiration. 


J^'ig.   liy. — .^Schema  of  Kespiratury  Mechanism  in  Expiration. 
(  Laulanie.  ) 

Th,  Thoracic  cavity  having  at  its  base  an  elastic  membrane,  having  a  cord 
attached  which  makes  traction  in  a  vertical  direction  on  the  elastic  membrane 
which  represents  the  diaphragm.  The  bottle  has  a  cork  with  three  openings. 
t.  Represents  the  trachea  opening  into  a  rubber  balloon.  Po,  Representing  a 
lung,  t".  Connecting  the  interior  of  the  bottle  with  a  mercurial  manometer. 
t',  A  tube  with  a  clamp  to  be  put  on  when  the  rubber  lung  has  been  inflated; 
it  connects  the  space  Th,  which  represents  the  pleural  cavity. 

The  diaphragm  is  supplied  by  the  phrenic  nerves. 

In  addition  to  the  diaphragm,  inspiration  is  aided  by  the  raising 
of  the  ribs  and  sternum.  Since  the  ribs  are  hinged  posteriorly  to 
the  vertebral  column,  it  is  their  lateral  and  anterior  portions  which 
possess  the  most  motion;  that  is,  their  direction  is  slightly  forward 
and  upward. 


RESPIRATION. 


313 


In  ascending,  the  ribs  straighten  upon  the  spinal  column,  and, 
instead  of  the  lower  ones  in  particular  being  so  oblique,  are  now 
found  to  occupy  a  more  nearly  horizontal  plane.  This  increases  the 
antero-posterior  diameter.  At  the  same  time  that  the  ribs  are  raised 
they  undergo  a  movement  of  rotation,  by  virtue  of  which  they  sep- 
arate from  the  median  line  of  the  chest.  It  is  this  movement  which 
produces  an  enlargement  of  the  thorax  in  its  lateral  diameter  at  the 
same  time  the  antero-posterior  diameter  is  slightly  increased. 


Fig.  120. — Schema  of  Action  of  Intercostal  Muscles.      (Landois.) 

I.  When  the  rods  a  and  6  which  represent  the  ribs  are  raised,  the  inter- 
costal   space    must   be    widened    (e,    f  —  c,    d).     On   the   opposite   side    when    the 

rods  are  raised  the  line  g-h  is  shortened  (i,  k  —  g.  It),  the  direction  of  the 
external  intercostal,  l-m,  is  lengthened  (/,  m  —  o,  n)  in  the  direction  of  the 
internal   intercostals. 

II.  When  the  ribs  are  raised  the  intercartilaginei  indicated  by  g-h  and  the 
external  intercostals  indicated  by  l-k  are  shortened.  When  the  ribs  are  raised 
the  position  of  the  muscular  fibers  is  indicated  by  the  diagonals  of  the  rhombs 
becoming  shorter. 

During  inspiration  the  ril^s  are  raised,  when  the  breathing  is 
ordinary,  by  the  external  intercostals.  The  scaleni  and  costal  ele- 
vators also  are  of  service.  When  respiration  is  governed  by  the 
latter  muscles,  the  lower  part  of  the  chest  possesses  the  greater  ex- 
pansion. The  reverse  is  true  when  inspiration  is  forced,  for  then 
the  upper  antero-posterior  diameter  becomes  the  greater. 


314  PHYSIOLOGY. 

During  extraordinary  inspiration — as  that  caused  by  violent 
muscular  exercise  or  when  some  pathological  condition  is  present  so 
that  air  finds  its  way  into  the  chest  only  as  the  result  of  strong  mus- 
cular efi:'ort — the  other  muscles  are  called  into  service. 

These,  the  emergency  muscles,  are  very  probably  the  sterno- 
cleido-mastoids,  the  serrati  magni,  the  pectorals,  and  the  trapezii. 

Expiration. — -Expiration,  when  it  is  effected  with  the  aid  of 
muscular  powers,  has  as  its  causative  agents  the  internal  intercostals, 
the  triangularis  sterni,  the  two  oblique  and  transverse  muscles  of  the 
abdomen,  and  quadratus  lumborum.  It  is  in  complex  expiration — as 
crying,  coughing,  singing,  expectoration,  sneezing,  etc. — that  the  pre- 
ceding muscles  enter  into  contraction.  The  abdominal  muscles  are 
the  most  powerful  in  the  above-named  group.  In  general,  it  may  be 
said  that  any  and  all  muscles  concerned  in  the  depression  of  the  ribs 
belong  to  the  expiratory  set  of  muscles. 

On  the  contrary,  ordinary  expiration  can  be  effected  by  the  mere 
relaxation  of  those  factors  concerned  in  the  production  of  inspiration. 
During  this  relaxation  the  thoracic  and  abdominal  walls,  by  reason 
of  their  elasticity,  compress  the  air-distended  lungs,  and  by  so  doing 
compel  expiration.  The  lung-tissue  itself  helps  to  the  extent  of  its 
own  elasticity.  The  expenditure  of  that  power  and  energy  necessary 
to  produce  inspiration  now  becomes  the  expiratory  exponent.  Dur- 
ing ordinary  and  tranquil  breathing  this  elastic  recoil  of  the  stretched 
components  is  amply  sufficient  to  expel  the  air  from  the  lungs.  Thus 
no  muscular  energy  is  required  to  perform  expiration. 

A  normal  lung  is  never  able  to  contract  to  its  fullest  ability, 
since  it  is  always  distended  to  some  extent  by  reason  of  its  cohesive 
attraction  with  the  interior  of  the  chest-walls,  as  well  as  because  of 
the  presence  of  a  certain  proportion  of  air  within  the  vesicles  which 
exerts  an  expansive  pressure. 

It  is  interesting  to  note  that,  though  the  expiratory  muscles  be 
more  numerous  and  powerful  than  the  inspiratory  ones,  it  is  because 
the  former  are  intended  especially  for  complex  expiration;  that  is  to 
say,  violent  actions,  since  ordinary  expiration  is  able  to  be  effected  by 
the  mere  elasticity  of  the  parts.  During  expiration  the  lungs,  which 
were  dilated,  return  upon  themselves,  so  that  they  let  out  a  quantity 
of  air  nearly  corresponding  to  that  which  entered  at  first.  The  lungs, 
which  are  seen  to  be  entirely  passive  during  inspiration,  can  partici- 
pate actively  in  expiration,  particularly  in  such  complex  acts  as  ex- 
pectoration, coughing,  etc. 

There  are  various  modes  of  respiration  in  man  and  in  mammals 


RESPIRATION. 


315 


which  are  usually  classed  under  three  principal  types.  In  the  abdom- 
inal type,  characteristic  among  children,  the  ribs  remain  motionless 
and  the  respiratory  action  is  revealed  only  by  the  movements  of  the 
abdominal  wall;  this  becomes  projecting  during  inspiration  and 
sinks  during  expiration.  In  the  inferior  costal  type,  man's  type,  the 
respiratory  movements  take  place  especially  at  the  level  of  the  lower 
ribs,  beginning  with  the  seventh.  Finally,  in  the  superior  costal,  or 
clavicular,  type,  the  respiratory  movements  are  very  manifest  only 
about  the  upper  ribs,  especially  the  first,  which  are  carried  upward 
and  forward.  The  clavicle  also  participates  in  this  movement.  This 
last  type  is  the  mode  of  respiration  peculiar  to  woman,  who  pre- 
sents it  very  early.  The  state  of  pregnancy,  which  would  greatly 
interfere  with  the  other  types  of  respiration,  does  not  hinder  breath- 
ing very  much  in  this  last  type,  since  the  movements  take  place 
naturally  at  the  upper  part  of  the  chest. 


Fig.   121.— Tracing  of  a  Respiratory  Movement.     (Foster.) 

A  whole  respiratory  movement  is  comprised  between  a  and  a,  inspiration 
extending  from  a  to  6  and  expiration  from  b  to  a.  The  waves  at  c  are  caused 
by  heart-beats. 

The  superior  costal  t^'pe  is  found  perfectly  established  in  girls 
and  women  who  have  never,  worn  a  corset,  and  this  is  probably  due 
to  heredity.  Mays  and  Kellogg  have  found  that  pure-blooded  Indian 
girls,  who  have  never  worn  corsets,  usually  have  the  abdominal  type 
and  not  the  costal  type  of  respiration. 

Among  animals  the  abdominal  type  of  respiration  is  found  in 
the  horse,  the  cat,  the  rabbit,  and  the  inferior  costal  type  in  the  dog. 

The  Stethograph,  or  Pneumograph. — To  gain  an  exact  idea  of 
the  time  occupied  in  the  various  phases  of  respiration  it  becomes  neces- 
sary to  obtain  its  curve,  or  pneumatogram.  The  apparatus  for  re- 
cording these  respiratory  movements  is  termed  a  stethograph,  or 
pneumograph. 

The  simplest  form  of  stethograph  is  that  of  Brondgeest.  It  con- 
sists of  a  brass  saucer-shaped  vessel  covered  with  a  double  layer  of 


316 


PHYSIOLOGY. 


Fig.  122. — Marey's 

Tympanum  and  Lever. 

(  Sanderson.  ) 

A,  Lever.  B.  Tympanum. 
P,  Tube  which  communi- 
cates with  cavity  of  the 
tympanum  and  connects 
with  the  tracheal  cannula 
or  the  cardiograph. 


rubber  membrane.  The  air  is  forced  in  between  the  two 
la}X'rs  until  the  external  layer  bulges  outward.  This 
stethograph  is  placed  in  position  on  the  chest  by  means  of 
tapes.  The  cavity  of  the  saucer-shaped  apparatus  com- 
municates with  a  recording  tambour,  which  writes  down 
the  movements  on  a  revolving  smolvcd  drum. 

The  resultant  curve,  known  as  the  pneumatogram, 
shows  that  the  acts  of  expansion  and  contraction  of  the 
chest-wall  consume  nmrly  equal  times.  The  ascending 
limb  (inspiration)  is  begun  with  moderate  rapidity,  be- 
comes accelerated  in  the  middle  of  its  course,  to  be  again 
slowed  at  its  end.  The  descending  limb  (expiration)  shows 
the  same  characteristics  as  to  its  construction,  thereby 
giving  a  gradual  fall  to  the  curve. 

Inspiration  is  Slightly  Shorter  than  Expira- 
tion.— For  all  2)ractical  purposes  it  may  be  stated  that  the 
average  respiratory  rliythm  is :  Inspiration  :  expiration  : : 
5 :  6.  However,  it  is  known  that  various  authors  give  dif- 
ferent ratios,  and  in  women,  children,  and  old  people  6  to 
8  or  ()  to  9  may  be  found.  Immediately  following  expira- 
tion there  is  a  slight  pause. 

Cases  are  rather  rare  in  which  the  dura- 
tion of  inspiration  and  expiration  are  equal,  or 
that  of  expiration  shorter  than  insjjiration. 
When  the  respiratory  movements  are  studied 
as  depicted  on  the  pneumatogram,  it  is  found 
that  there  is  practically  no  pause  between  the 
end  of  inspiration  and  the  beginning  of  expira- 
tion. 

RESPIRATORY  SOUNDS. 

If  a  stethoscope  is  placed  over  a  portion  of 
a  lung  at  some  distance  away  from  the  trachea 
and  larger  bronchi,  a  sound  will  be  heard  the 
character  of  which  is  variously  described  as  soft 
or  sighing,  resembling  the  rustling  of  leaves  in 
a  slight  wind.  The  sound  is  heard  during  the 
whole  of  inspiration  and  is  followed  by  a  short 
expiratory  sound.  The  inspiratory  sound  is 
three  times  the  length  of  the  expiratory.  It 
must  be  remembered  that  the  movements  of 


RESPIRATION. 


317 


inspiration  are  to  those  of  expiration  in  point  of  time  as  5  to  6, 
while  the  vesicular  sound  of  inspiration  is  to  that  of  expiration  as 
3  to  1.  The  cause  of  vesicular  sound,  according  to  one  theory,  is 
supposed  to  arise  from  the  passing  of  air  into  and  out  of  the  alveoli 
and  infundibula,  the  friction  here  generating  a  sound,  aided  by  the 
sudden  dilatation  of  the  air-vesicles. 

If  now  the  stethoscope  is  placed  over  the  trachea  just  above  the 
suprasternal  notch,  two  sounds  are  heard:    one  during  inspiration, 

the  other  during  expiration.     They  are 

not  of  equal  length;  the  inspiratory  is 
the  longer.  The  quality  of  both  sounds 
may  be  described  as  blowing,  tubular,  or 
bronchial.  The  expiratory  part  is  more 
intense  and  frequently  of  higher  pitch. 
This  bronchial  sound  is  produced  by  air 
in  passing  through  the  chink  of  the 
glottis,  which  is  thrown  into  vibration, 
and  imparts  its  motion  to  the  columns  of 
air  in  the  trachea  and  bronchi. 

In  practical  medicine  it  is  inferred 
that,  when  the  vesicular  murmur  is 
heard  over  any  portion  of  the  lung-tis- 
sue, this  area  being  properly  distended, 
the  lung  is  in  a  healthy  condition.  If, 
however,  the  expiratory  portion  of  it  be- 
comes loud  and  prolonged,  it  excites 
inquiry. 


i'ig.    123. — kSpiioiueter. 
(Fredebicque.) 


QUANTITY  -OF   AIR   BREATHED. 

The  determination  of  the  volume  of 
E,  Mouth-piece,    c.  Chamber        -j,    ^eccssary    to    the    necds    of    human 

to  receive   the   air   expired.  -^ 

respiration  is  a  problem  that  has  re- 
ceived much  attention.  Because  of  a  multitude  of  circumstances, 
both  external  as  well  as  those  that  are  proper  to  the  individual  himself, 
the  figures  representing  the  quantity  of  air  that  enters  the  lungs  at 
each  inspiration  and  the  quantity  that  leaves  them  at  each  corres- 
ponding expiration  can  scarcely  have  more  than  an  approximate  value. 
Xeverthelesp,  results  Avhich  sufficiently  agree  to  permit  of  establish- 
ing an  average  of  the  quantity  of  air  put  in  circulation  during  each 
normal  respiratory  movement  have  been  arrived  at.  It  is  very  gen- 
erally admitted  that  in  an  adult  and  healthy  man,  each  inspiration 


318  PHYSIOLOGY. 

iutroduces  into  the  pulmonary  apparatus  about  20  cubic  inches 
of  air. 

Among  the  numerous  observers  who  have  occupied  themselves 
with  the  study  of  the  quantity  of  air  put  into  circulation,  Herbst  and 
Hutchinson,  in  particular,  may  be  cited.  The  latter's  spirometer  is 
the  instrument  which  has  been  most  frequently  used  to  secure  data 
in  experiments  along  this  line.  It  represents  essentially  a  gaso- 
meter. It  is  furnished  with  a  fixed  scale  and  a  movable  indicator; 
the  latter  follows  the  movements  of  the  air  receiver  and  indicates 
them  on  the  graduated  scale.  The  receiver  dips  into  a  reservoir 
filled  with  water  and  communicates  with  the  chest  of  the  experi- 
menter by  means  of  a  rubbfer  tube  ending  in  a  glass  or  metal  funnel. 

To  measure  the  volume  of  air  concerned  in  exaggerated  respira- 
tion, the  experimenter  is  made  to  stand  up,  care  being  taken  that  his 
chest  is  free  from  any  restraint  that  would  hinder  the  mobility  of  his 
chest.  After  several  forceful  inspirations  and  expirations,  he  inhales 
the  greatest  quantity  of  air  that  he  can  draw  into  his  lungs.  With 
the  tube  of  the  spirometer  between  his  lips  he  then  makes  the  fullest 
possible    expiration. 

By  subjecting  about  two  thousand  persons  to  this  test  Hutchin- 
son recognized  that  the  quantity  of  air  which  a  maximum  inspiration 
and  expiration  can  put  into  circulation  varies  according  to  the 
individual.  It  is  230  cubic  inches  for  a  man  5  feet  8  inches  in 
stature.  According  to  this  observer,  the  prime  factor  in  producing 
variance  in  pulmonary  capacity  is  mainly  the  size  of  the  individual. 

For  every  inch  of  height  from  5  feet  to  6  feet,  8  additional 
cubic  inches  are  given  out  by  a  forceful  expiration  after  a  full 
inspiration.  Vice  versa,  for  every  inch  below  the  5-foot  mark  the 
capacity  is  diminished  by  the  same  amount. 

The  mobility  of  the  thoracic  walls  has  here  a  real  influence. 
Persons  with  narrow  chests  are  sometimes  found  who  can  dilate  the 
thorax  much  more  than  those  in  whom  the  circumference  of  that 
part  of  the  body  is  greater.  With  equal  dimensions,  the  number 
indicated  by  the  spirometer  increases  with  the  dilatability  of  the 
thorax. 

The  individual's  capacity  appears  to  be  greatest  in  the  period 
from  the  twenty-fifth  to  the  fortieth  year,  showing  a  gradual 
increase  until  the  latter  mark  is  reached.  From  this  point  it  begins 
to  diminish,  to  become,  in  old  age,  less  than  it  was  even  in  youth. 

Observers  agree  in  admitting  that,  in  woman,  the  maximum 
volume  expired  is  perceptibly  less  than  in  man.     The  difference  is 


RESPIRATION,  319 

usually  represented  by  50  cubic  inches.  Abdominal  tumors,  what- 
ever their  nature  and  whatever  the  organ  affected,  have  the  constant 
effect  of  diminishing  the  volume  of  air  expired;  pregnancy  alone 
has  not  that  consequence. 

If  a  lung  from  an  animal  be  thrown  into  a  vessel  of  water,  it 
floats.  If  it  be  forcibly  submerged  and  then  squeezed,  bubbles  of 
air  will  find  their  way  to  the  water's  surface.  From  this  little 
experiment  the  student  knows  that,  even  though  the  lungs  be  col- 
lapsed, yet  they  contain  a  certain  amount  of  air  which  is  not  very 
readily  expelled.  This  is  the  air  that  is  held  within  the  confines  of 
the  small  alveoli  and  that  cannot  very  easily  find  its  way  through 
the  small  passageways  opening  into  them.  It  follows,  then,  that  all 
of  the  air  in  the  lungs  cannot  possibly  be  changed  during  each  res- 
piration, and  the  amount  that  is  changed  bears  a  very  close  rela- 
tionship to  the  type  of  respiration,  whether  it  be  forced  or  ordinary. 

1.  Tidal  Air. — The  volume  of  air  that  is  introduced  into  the 
lungs  during  ordinary  inspiration  by  an  adult  in  good  health  is 
termed  tidal  air.     It  is  20  cubic  inches. 

The  tidal  air  finds  its  way  into  and  out  of  only  the  larger  bron- 
chial vessels,  where  it  comes  in  contact  with  the  nearly  stationary 
columns  of  air  which  extend  through  the  smaller  bronchial  tubes. 
The  interchange  between  the  two  columns  is  by  a  process  of  diffusion. 
By  this  means  does  the  oxygen  find  its  way  into  the  blood  flowing 
through  the  capillaries,  while  the  carbonic  acid  makes  its  way  into 
the  larger  bronchial  tubes  to  be  finally  expelled  from  the  body. 

2.  Complemental  Air  is  the  quantity  of  air  which  we  are  able 
to  inspire  with  the  greatest  effort  over  and  above  that  of  ordinary 
breathing.     The  average  is  estimated  by  volume  as  110  cubic  inches. 

3.  Reserved  Air,  or  supplemental  air,  is  the  quantity  of  air 
remaining  in  the  lungs  after  an  ordinary  expiration  that  would  be 
expelled  by  the  fullest  effort.  It  is  considered  to  be  about  100  cubic 
inches. 

4.  Residual  Air  is  'that  which  remains  in  the  lungs  after  the 
fullest  possible  expiration  and  cannot  be  expelled  by  any  voluntary 
effort.     Its  volume  is  also  100  cubic  inches. 

5.  The  Vital  Capacity  is  the  tidal,  complemental,  and  reserved 
airs  added  together,  and  is  230  cubic  inches.  It  represents  the 
amount  of  air  which  a  person  is  able  to  expel  from  his  lungs  after 
the  deepest  possible  inspiration.  One-sixth  of  the  air  in  the  lungs 
is  renewed  at  each  ordinary  respiration. 

Professor  Gad,   of  Prague,  has  constructed   an  instrument   to 


320  PHYSIOLOGY. 

measure  the  volume  of  the  air  expired  and  inspired.  It  is  called 
an  aeroplethysmograph.  It  consists  of  two  boxes,  one  inside  the 
other;  the  space  between  is  filled  with  water.  The  inside  mica  box 
receives  the  air  expired.  At  its  posterior  surface  there  is  an  axis 
which  allows  the  anterior  surface  to  elevate  and  depress  itself.  The 
movements  of  the  mica  box  are  recorded  by  a  pen  attached  to  it. 
The  box  itself  is  counterpoised  by  a  weight.  The  instrument  must 
be  graduated,  in  order  that  one  may  determine  the  volume  of 
inspired  and  expired  air. 

NUMBER  OF  RESPIRATIONS. 

In  an  adult,  the  number  of  respirations  per  minute  may  vary 
from  IG  to  3-1.  It  is  usually  stated  that  -i  pulse-beats  occur  during 
each  respiration.     The  numlier  is  varied  by  the  position  of  the  body; 


Fig.    124. — Gad's   Aeropletliysmograph.      (IvRUSicii.) 

thus,  there  may  be  counted  13  while  recumbent,  19  in  the  sitting 
posture,  and  23  respirations  per  minute  while  standing. 

During  infancy  and  childhood  the  number  of  respirations  is 
always  greater  than  in  the  adult.  Exercise  temporarily  increases 
respiration  both  as  to  number  and  to  depth.  It  is  believed  that 
there  is  some  product  derived  from  the  metabolism  of  muscles  which 
acts  as  the  respiratory  stimulant. 

Every  athlete  knows  of  that  condition  popularly  termed  "second 
wind."  At  the  beginning  of  severe  exercise  there  is  a  marked 
dyspnoea  which  passes  away  after  a  short  time,  even  though  the  exer- 
cise be  uninterrupted.  It  cannot  be  explained  physiologically,  but 
is  believed  to  be  in  a  very  great  measure  cardiac. 

Pathological. — Respirations  may  be  increased  by  reason  of  fever, 
])lcurisy,  pneumonia,  some  heart  diseases,  and  anjemia.  Diminution 
is  occasioned  by  pressure  upon  the  respiratory  center  in  the  medulla; 
this  occurs  in  coma. 


RESPIRATION. 


321 


PRESSURE  IN  THE  AIR=PASSAQES  DURING  RESPIRATION. 

It  has  been  previously  stated  that  even  after  the  deepest  expira- 
tion the  lungs  are  never  completely  collapsed.  They  are  still  "on 
the  stretch"  by  reason  of  the  elastic  fibers  contained  in  them. 

The  reason  for  the  collapsing  of  the  lungs  when  the  chest  is 
opened  is  that  the  pressure  upon  the  pleural  and  alveolar  surfaces 
is  now  equal,  being  that  of  the  pressure  of  the  atmosphere.  The 
pressure  of  the  residual  air  was  sufficient  to  overcome  the  elasticity 
of  the  muscular  fibers  of  the  lungs.  As  long  as  the  chest-wall  was 
unopened  the  lungs  contracted  only  until  their  elasticity  was  just 


Fig.  125. — Number  of  Respirations  by  Man  at  Different  Ages. 
(QuETELET. )  (From  Tigerstedt's  "Human  Physiology,"  copyright,  1906, 
by  D.  Appleton  and  Company.) 

Read  from  left  to  right. 

balanced  by  the  outward  pressure  of  the  contained  air.  In  intra- 
uterine life,  and  in  stillborn  children  who  have  never  breathed,  the 
lungs  are  completely  collapsed  (atelectasis).  If  the  lungs  be  once 
inflated  they  never  completely  collapse  so  long  as  the  thoracic  walls 
be  not  pierced. 

When  a  manometer  was  attached  to  the  trachea  of  an  animal 
so  that  its  respirations  proceeded  unchecked,  every  inspiration 
showed  a  negative  pressure,  every  expiration  a  positive  pressure. 
An  observer  placed  a  U-shaped  manometer  tube  in  one  of  his  nos- 
trils, closed  his  mouth,  let  the  other  nostril  open,  and  then  respired 
quietly.     During  every  inspiration  there  was  a  negative  pressure  of 

21 


322  PHYSIOLOGY. 

1  millimeter  of  mercury,  during  expiration  a  positive  pressure  of 
from  2  to  3  millimeters. 

Forced  respirations  produce  great  variations  from  the  above 
figures.  The  greatest  negative  pressure  averaged  — •  57  millimeters 
of  mercury  during  inspiration;  the  maximum  positive  pressure  dur- 
ing expiration  averaged  -j-  8"^  millimeters. 

The  greater  part  of  the  force  exerted  in  deep  inspiration  is  used 
in  overcoming  the  resistance  offered  by  the  elasticity  of  the  lungs, 
the  raising  of  the  weight  of  the  chest,  and  depressing  the  abdominal 
contents.  These  resisting  forces  acting  during  expiration  aid  the 
expiratory  muscles;  from  this  it  follows  that  the  forces  concerned 
in  expiration  are  much  greater  than  those  of  inspiration. 

Expiration  is  longer  and  stronger  than  inspiration,  but  the 
sound  of  inspiration  is  longer  than  that  of  expiration. 


Fig.   126. — Carotid  Pressure  in  Dog.     Acceleration  of  Heart  at  the 
Moment  of  Inspiration  is  Well  Marked.      (Langlois.  ) 

EFFECT  OF  RESPIRATION  ON  THE  CIRCULATION. 

When  a  kymographic  tracing  in  an  animal  is  taken  there  are 
seen  rises  and  falls  in  it,  due  to  the  acts  of  respiration.  Shortly 
after  the  commencement  of  an  inspiration  the  arterial  tension 
reaches  its  maximum,  and  immediately  after  an  expiration  it  begins 
to  fall,  reaching  its  lowest  level  after  the  beginning  of  the  subse- 
quent inspiration. 

The  pulse  is  more  rapid  during  an  inspiration  than  during  an 
expiration.  I  shall  now  inquire  into  the  causes  of  these  two  changes : 
(1)  those  of  blood-pressure,  and  (2)  the  increased  frequency  of  the 
pulse. 

The  walls  of  the  air-cells  have  an  elastic  force  which  is  greater, 
the  greater  the  distension. 

This  elastic  force  will  cause  collapse  of  the  lung  and  exerts  a 
suction-like  action  on  the  contents  of  the  chest.  This  negative 
pressure  becomes  greater  and  greater  as  the  lungs  are  distended. 


RESPIRATION. 


323 


This  negative  pressure  is  called  the  intra-thoracic  or  intra-pleural, 
not  intra-pulmonic,  pressure,  and  is  always  less  than  the  air-pres- 
sure. Intra-thoracic  pressure  is  the  pressure  in  the  pleural  cavity 
and  mediastinum.  The  pressure  necessary  to  counterbalance  the 
elasticity  of  the  lungs  when  they  are  quiescent  in  the  pause  of  res- 
piration is,  in  man,  7  millimeters  of  mercury,  and  when  the  lungs 
are  fully  distended  it  rises  to  30  millimeters  of  mercury. 

The  pressure  in  the  pleural  cavity  is  less  than  an  atmosphere; 
it  is  a  negative  pressure,  and  is  due  to  the  fact  that  the  lungs  are 
smaller  than  the  thoracic  cavity  in  which  they  lie. 


Fig.  127. — Apparatus  to  Illustrate  Relations  of  Intra-tlioracic  and 
External  Pressures.  (After  Beaunis.)  (From  Mills's  "Animal  Physi- 
ology," copyright,  1889,  by  D.  Appleton  and  Company.) 

A  glass  beU-jar  is  provided  with  a  light  stopper,  through  which  passes  a 
branching  glass  tube  fitted  with  a  pair  of  elastic  bags  representing  lungs.  The 
bottom  of  the  jar  is  closed  by  rubber  membrane  representing  diaphragm.  A 
mercury  manometer  indicates  the  difference  in  pressure  within  and  without  the 
bell-jar.  In  the  left-hand  figure  it  will  be  seen  that  these  pressures  are  equal; 
In  right  (inspiration),  the  external  pressure  is  considerably  greater.  At  one 
part  (6)  an  elastic  membrane  fills  a  hole  in  jar,  representing  an  intercostal 
space. 

It  follows,  then,  that  with  a  full  inspiration  the  pressure  exerted 
upon  the  cardiac  organs  in  the  chest  is  30  millimeters  less  than  that 
of  the  air-pressure  of  760  millimeters  of  mercury. 

When  the  waves  of  blood-pressure  are  compared  with  the  curves 
of  the  movements  of  respiration  or  with  the  variations  of  intra- 
thoracic pressure,  it  is  found  that,  while  arterial  tension  rises  dur- 
ing inspiration  and  falls  during  expiration,  neither  the  rise  nor  the 
fall  is  exactly  synchronous  with  either  inspiration  or  expiration. 

In  inspiration,  the  flow  of  blood  from  the  veins  outside  the  chest 
is  pressed  towards  the  inside  of  the  chest,  because  the  air-pressure 


324 


PHYSIOLOGY. 


outside  the  chest  exceeds  the  air-pressure  within  the  chest.  Hence  a 
larger  amount  of  blood  enters  the  right  auricle  during  inspiration. 
This  being  ejected  by  the  right  ventricle,  the  pulmonary  capillaries, 
having  less  jjressure  externally,  let  the  blood  pass  in  larger  quan- 


Imp'fahon. 


I  £)ifytrafierL 


Fig.  128. 

tity  and  the  left  ventricle  forces  out  more  blood  into  the  aorta  and  the 
arterial  blood-pressure  rises.  During  expiration,  the  pressure  on  the 
heart  and  blood-vessels  inside  the  chest  returns  to  normal ;  hence  the 
atmospheric  pressure  outside  the  chest  does  not  drive  the  blood  from 
the  veins  into  the  chest,  as  in  inspiration,  hence  less  blood  goes  into 
the  right  side  of  the  heart,  and,  as  the  pulmonary  vessels  are  also 


Fig.    129. — Comparison    of    Blood-Pressure    Curve    with    Curve   of    Intra- 
thoracic Pressure.     (M.  Foster.) 

(To  be  read  from  left  to  right.)  a  is  the  cm  ve  of  blood-pressure  with  its  respira- 
tory undulations,  the  slower  beats  on  the  descent  being  very  marked  ;  b  is  the  curve  of 
the  intra-thoracic  pressure  obtained  by  connecting  one  limb  of  a  manometer  with  the 
pleural  cavity.  Inspiration  begins  at  i  and  expiration  at  e.  The  intra-thoracic  pressure 
rises  very  rapidly  after  the  cessation  of  the  inspiratory  effort,  and  then  slowly  falls  as 
the  air  issues  from  the  chest ;  at  the  beginning  of  the  inspiratory  effort  the  fall  becomes 
more  rapid 

pressed  upon,  a  less  quantity  of  blood  goes  to  the  left  ventricle  and 
out  into  the  aorta  ;  hence  a  fall  of  blood-pressure. 

The  pulmonary  capillaries  in  the  lungs  contain  more  blood  in 
inspiration  because  the  inspiratory  act  tends  to  dilate  them.     The 


RESPIRATION.  325 

effect  of  the  distension  is  to  increase  the  flow  of  blood  in  the  lungs, 
because  the  widened  arterioles  decrease  the  resistance  to  the  flow.  In 
expiration,  the  pulmonary  capillaries  are  lessened  in  diameter,  and 
the  narrowing  of  the  capillaries  increases  the  resistance  to  the  flow  of 
blood.  Hence  it  is  the  quantity  of  blood  in  the  left  ventricle  which, 
during  inspiration  and  expiration,  elevates  and  depresses  the  blood- 
pressure. 

Wherefore,  on  making  a  tracing  of  both  the  respiratory  move- 
ments and  the  blood-pressure,  it  is  discovered  that  the  blood-jDressure 
falls  slightly  at  the  beginning  of  inspiration,  but  rises  during  the 
rest  of  the  movement.  At  the  beginning  of  expiration  the  pressure 
continues  to  rise  for  a  short  time,  and  then  falls  during  the  rest 
of  the  act. 

The  arteries  and  veins  are  differently  affected  by  the  respira- 
tory movements.     According  to  Foster,  the  arch  of  the  aorta  has  an 


'^Carotid. 


Normal 
rArteriaf 
B/sod  rressttre 


Fig.  130. 


inclination  to  expand,  from  the  decrease  of  intra-pleural  pressure  in 
the  thorax  during  inspiration,  which  temporarily  retards  the  flow  of 
blood  and  diminishes  aortic  pressure. 

The  aorta  during  expiration  tends  to  contract,  because  expira- 
tion increases  the  thoracic  pressure  outside  the  aortic  arch,  which 
temporarily  increases  the  blood-pressure  in  the  aorta.  Hence  in  in- 
spiration the  arterial  pressure  temporarily  diminishes.  During 
expiration  the  arterial  pressure  temporarily  increases. 

The  blood-vessels  of  the  lungs  enlarge  during  inspiration  and 
thus  become  more  distended  with  blood,  and  thus  retain  for  a  while 
a  certain  quantity  of  blood  in  the  lungs  and  thus  diminish  the 
amount  falling  into  the  left  auricle.  But  this  is  only  temporary, 
because  the  widening  of  the  vessels  would  permit  an  increased  flow 
of  blood  in  the  pulmonary  vessels,  due  to  diminished  resistance  of 
the  dilated  passages,  and  a  contrary  result  would  ensue. 

Vice  versa,  the  first  effect  of  expiration  would  increase  the  flow 
in  the  left  auricle,  due  to  the  additional  quantity  of  blood  driven  on 
by  the  partial  shrinking  of  the  vessels  of  the  lungs,  followed  by  a 
more  decided  diminished  flow  caused  by  great  resistance  of  the  con- 


326  RESPIRATION. 

tracted  pulmonary  vessels.  Hence  inspiration  first  diminishes  the 
flow  of  blood  into  the  left  auricle  and  necessarily  in  the  left  ven- 
tricle, but  afterwards  for  the  rest  of  inspiration,  until  the  beginning 
of  expiration,  it  increases  the  flow  into  the  ventricle. 

Vice  versa,  expiration  temporarily,  at  flrst,  increases  and  after- 
wards diminishes  the  flow  of  blood  into  the  left  ventricle. 

The  influence  of  thoracic  negative  pressure  during  inspiration 
and  the  return  in  a  positive  direction  during  expiration  will  have 
more  efl^ect  on  the  pulmonary  veins  with  their  thin  walls  than  on  the 
thicker-walled  pulmonary  artery — that  is,  during  inspiration  there 
will  be  a  diminution  of  pressure  in  the  pulmonary  veins  greater  than 
that  in  the  pulmonary  artery,  and  this  will  be  an  added  influence  in 
favoring  the  flow  into  the  left  yontricle.  In  expiration,  a  similar  dif- 
ference will  be  observed  in  the  contrary  direction.  The  left  ventricle, 
from  the  increased  flow  of  blood,  will  throw  a  larger  amount  of 
blood  and  the  arterial  pressure  will  rise. 

JnspirafioTL 


Fig.    1.31. 

Vice  versa,  decrease  of  flow  of  blood  into  the  ventricle  will  cause 
the  arterial  pressure  to  fall. 

The  respiratory  movement  on  the  vessels  of  the  lungs  at  the 
beginning  of  inspiration  will  continue  the  lowering  of  the  blood- 
pressure  which  was  taking  place  during  expiration,  but  afterwards 
will  raise  it.  Vice  versa,  at  the  beginning  of  expiration  it  continues 
the  rise  of  arterial  pressure  which  was  going  on  during  inspiration, 
but  afterwards  lowers  the  tension  in  the  arteries. 

In  studying  the  action  of  the  respiratory  movements  on  blood- 
pressure,  we  must  remember  that  in  the  descent  of  the  diaphragm 
in  inspiration  it  presses  upon  the  viscera  of  the  abdomen  and  forces 
at  first  a  quantity  of  blood  along  the  vena  cava  inferior,  but  sub- 
sequently retards  the  ascent  of  the  blood  from  the  abdomen  and  the 
inferior  extremities.  In  normal  expiration,  the  diaphragm  ascends, 
and  the  viscera,  not  being  so  forcibly  pressed  upon,  deliver  less  blood 
by  the  inferior  vena  cava  to  the  heart. 

During  inspiration,  the  heart's  frequency  is  greater  than  during 
expiration  and  the  pulse-curve  is  somewhat  different.     If  the  vagi 


RESPIRATION.  327 

are  divided,  there  is  no  difference  in  the  pulse-rate  during  inspiration 
and  expiration.  Now,  Hering  has  shown  that  distension  of  the 
lungs  irritates  the  afferent  nerves  of  the  vagus  center  whose  impulses 
inhibit  the  cardio-inhibitory  centers  and  allow  the  heart  to  run  faster. 
Another  cause  of  the  increased  raj)idity  of  the  heart  in  inspiration 
is  the  spreading  of  impulses  from  the  respiratory  center  to  the  vagus 
center,  inhibiting  its  activity,  and  at  the  same  time  these  radiations 
of  impulses  from  the  respiratory  center  are  inhibiting  the  vasomotor 
center.  The  respiratory  center,  the  vagus  center,  and  the  vasomotor 
center  are  connected  by  association  fibers,  and  impulses  can  spread 
from  the  respiratory  center  over  to  the  others. 

Artificial  Respiration. — When  in  artificial  respiration  air  is 
driven  into  the  lungs  through  a  tracheal  cannula  with  sufficient  pres- 
sure, then  the  pulmonary  circulation  is  arrested.  Hence  there  is  an 
opposite  effect  produced  between  artificial  respiration  and  natural 
respiration  as  regards  their  influence  upon  the  course  of  the  blood. 

The  aspirating  action  of  the  thorax  may  suck  air  into  a  vein  in 
surgical  operations,  which,  on  being  transported  to  the  right  side  of 
the  heart,  may  block  the  pulmonary  capillaries  and  cause  a  sudden 
death. 

THE  FUNCTION  OF  THE  UNSTRIPED  MUSCLE  OF  THE 
BRONCHIAL  SYSTEM. 

If  a  dog  is  curarized,  the  interior  of  a  small  hronchus  is  con- 
nected with  a  recording  instrument  (the  chest  having  heen  opened), 
and  if  a  vagus  is  divided,  there  will  be  a  marked  expansion  of  the 
bronchi.  If  the  peripheral  end  of  the  vagus  be  stimulated,  then  a 
strong  contraction  of  the  bronchi  will  ensue.  It  is  evident  here  that 
the  smooth  muscles  of  the  bronchi  are  under  the  influence  of  the 
pneumogastrics.  These  effects  could  also  be  called  out  in  a  reflex 
manner.  This  explains  asthmas  due  to  reflex  irritations  transmitted 
to  the  centers  of  the  vagi.  Atropine  and  lobeline  paralyze  the  vagus 
ending  in  the  bronchial  muscles.  This  explains  their  utility  in  spas- 
modic asthma. 

VARIOUS  FEATURES  OF  RESPIRATION. 

Nasal  Breathing. — During  ordinar}',  quiet  breathing  most  peo- 
ple breathe  through  the  nostrils,  keeping  the  mouth  closed.  This 
is  very  proper  and  there  are  certain  advantages  to  be  derived  by  so 
doing.  Thus,  in  the  passage  of  the  air  through  the  nostrils,  whose, 
walls  are  narrow  and  somewhat  tortuous,  the  air  is  not  only  warmed, 


328  PHYSIOLOGY. 

but  rendered  moist  as  well.  By  this  means  there  is  prevented  the 
irritation  occasioned  by  cold,  dry  air  upon  the  lining  mucous  mem- 
brane. In  addition,  the  smaller  foreign  particles  are  caught  by  the 
mucous  lining  and  carried  outward  by  the  instrumentality  of  the 
ciliated  epithelium. 

Patholog^ical.— Pulmonary  oedema,  which  is  a  transudation  of 
lymph  into  the  pulmonary  alveoli,  occurs  (1)  when  there  is  very  great 
resistance  to  the  blood-stream  in  the  aorta  and  its  branches;  (2) 
when  the  pulmonary  veins  are  occluded;  (3)  when  the  left  ventricle, 
owing  to  mechanical  injury,  ceases  to  beat,  while  the  right  ventricle 
continues  in  its  contraction. 

Injection  of  muscarine  rapidly  produces  pulmonary  oedema  by 
reason  of  increased  pressure  and  slowing  of  the  blood-stream  in  the 
pulmonary  capillaries.  The  effects  of  this  drug  are  counteracted  by 
atropine. 

Relation  of  Respiration  to  the  Nervous  System. — Movements  of 
respiration  are  entirely  dependent  upon  the  nervous  system.  They 
are  nicely  balanced  actions,  performed  by  voluntary  muscles  under 
the  guidance  of  a  special  presiding  nerve-center,  namely:  the  respira- 
tory center.  Through  its  influence  the  muscles  of  inspiration  and 
expiration  are  kept  working  rhythmically  and  regularly,  whether  the 
individual  be  awake  or  sleeping.  Co-ordinated  impulses  are  con- 
stantly proceeding  from  the  center  to  the  muscles  involved.  How- 
ever, the  muscles  being  voluntary,  they  may  be  controlled  momen- 
tarily by  the  will,  and  respiration  be  made  entirely  to  cease  for  a 
minute  or  two.  Soon  Nature's  cry  for  oxygen  becomes  so  strong 
that  the  will  is  overcome  and  respiration  is  begim  again  under  the 
supervision  of  the  respiratory  center. 

The  Respiratory  Center. — This  center  is  located  in  the  medulla 
oblongata,  in  the  formatio  reticularis,  behind  the  superficial  origin 
of  the  vagi  and  on  both  sides  of  the  posterior  aspect  of  the  apex  of 
the  calamus  scriptorius.  Flourens,  its  discoverer,  found  that,  when 
destroyed,  respiration  ceases  at  once  and  the  animal  dies.  Hence 
he  termed  it  "the  vital  knot."  It  is  a  bilateral  center;  that  is,  it 
has  two  functionally  symmetrical  halves,  one  on  each  side  of  the 
median  raphe.  If  separated  by  means  of  a  longitudinal  incision,  the 
respiratory  movements  continue  symmetrically  on  both  sides.  De- 
struction of  one-half  of  the  medulla  is  attended  with  paralysis  of 
respiration  only  on  that  side,  seeming  to  prove  that  each  half  of  the 
center  is  particularly  concerned  in  the  respiratory  muscles  of  its 
own  side. 


RESPIRATION.  329 

During  ordinary  breathing  impulses  are  sent  from  the  respira- 
tory center  along  the  phrenics  to  the  diaphragm  and  along  the  inter- 
costal nerves  to  those  muscles  which  elevate  the  ribs. 

Impulses  and  messages  to  the  center  find  their  way  along  the 
fibers  of  the  vagi  nerves. 

While  it  seems  to  be  undisputed  that  the  principal  respiratory 
center  lies  in  the  medulla  and  that  upon  it  depends  the  rhythm  of 
the  respiratory  movements,  yet  there  have  been  found  other  and  sub- 
ordinate centers  located  in  the  cord.  These,  however,  are  reinforced 
by  the  main  one  in  the  medulla. 

The  cutaneous  nerves  also  exercise  some  effect  upon  respiration. 
The  most  marked  influence  is  exerted  by  those  of  the  face  (trigem- 
inus), abdomen,  and  chest.  Both  thermal  and  mechanical  stimuli 
easily  excite  them. 

Irritation  of  the  trigeminus  by  surgical  operation,  as  in  the 
removal  of  the  adenoids,  has  been  shown  by  Drs.  W.  H.  Good  and 
Harland  to  inhibit  the  respiratory  movements  and  the  cardiac  action. 
Hering  has  shown  that  inflation  of  the  lungs  causes  a  marked 
increase  in  the  number  of  heart-beats.  He  believes  that  the  sen- 
sory nerves  of  the  lungs  stand  in  the  same  relation  to  the  cardio- 
inhibitory  center  as  the  nervous  depressor  does  to  the  vasomotor 
center.  That  is,  irritation  of  the  sensory  terminals  in  the  lungs,  by 
inflation,  causes  reflexly  a  loss  of  tonus  in  the  cardio-inhibitory  cen- 
ter and  a  resulting  increment  of  heart-beats.  Dr.  Jackson,  in  a  case 
of  inhibition  of  the  heart  and  of  respiration  from  trigeminal  irrita- 
tion, resuscitated  a  patient  by  mouth-to-mouth  inflation.  Dr.  W.  H. 
Good  has  tried  artificial  inflation  on  animals  with  excellent  results, 
and  proposes  this  procedure  as  a  method  of  treatment  in  these  cases 
of  trigeminal  inhibition. 

Mechanical  stimulation  of  the  sensory  nerves  is  sometimes 
resorted  to  by  midwives.  It  is  well  known  that  to  arouse  a  sluggish 
respiratory  center  they  resort  to  slapping  the  buttocks  of  a  newborn 
chfld. 

During  the  act  of  deglutition  there  is  a  very  necessary  cessation 
of  breathing  for  a  short  period.  This  is  caused  by  stimulation  of 
the  central  end  of  the  glosso-pharyngeal  nerve. 

Section  of  the  cord  just  below  the  medulla  produces  an  arrest 
in  the  movements  of  not  only  the  intercostals,  but  even  the  dia- 
phragm. Section  of  one  phrenic  nerve  paralyzes  the  corresponding 
half  of  the  diaphragm;  division  of  both  nerves  causes  entire  cessa- 
tion of  movement  of  the  diaphragm.     The  phrenic  nerves  take  an 


330 


PHYSIOLOGY. 


RESPIRATION. 


331 


active  part  in  the  function  of  respiration.  When  these  nerves  are 
bared  and  irritated  there  is  noticed  a  rapid  movement  of  the 
abdomen  produced  by  contraction  of  the  diaphragm.  The  spasmodic 
movement  is  repeated  at  each  irritation  so  long  as  the  tissue  of  the 
nerve  remains  uninjured.  If  instead  of  mechanical,  an  electrical 
irritant  be  applied,  the  diaphragm  is  thrown  into  a  state  of  tetanic 
contraction  and  produces  death  from  asphyxia.  As  the  irritability 
of  the  phrenic  nerve  remains  a  long  time  after  death,  it  becomes 
easy  to  demonstrate  these  phenomena  without  causing  any  pain. 


Fig.  133. — Schema  of  the  Chief  Respiratory  Nerves, 
after  Rutherford.) 


(Landois, 


lys,  Inspiratory  center.  EXP,  Expiratory  center.  Motor  nerves  are  in 
unbroken  lines;  expiratory  motor  nerves  to  abdominal  muscles,  AB;  to 
muscles  of  back,  DO;  inspiratory  motor  nerves,  phrenics  to  diaphragm,  U. 
INT,  Intercostal  nerves.  RL,  Recurrent  laryngeal.  CX,  Pulmonary  fibers  of 
vagus  that  excite  inspiratory  center.  CX',  Pulmonary  fibers  that  excite 
expiratory  center.  CX",  Fibers  of  superior  laryngeal  that  excite  expiratory 
center.     IXH,  Fibers  of  superior  laryngeal  that  inhibit  inspiratory  center. 

After  section  of  the  vagi  the  heart's  movements  become  more 
rapid  and  the  respirations  slower.  At  the  end  of  some  minutes  the 
nares  dilate  a  little,  inspiration  is  accompanied  with  a  slight  noise, 
an  indefinite  restlessness  seems  to  seize  upon  the  animal  from  head 
to  foot;  it  moves  about  frequently,  and  raises  and  lowers  the  head 
as  if  there  was  a  constriction  of  the  throat.  At  length  the  anxiety 
of  the  animal  disappears;  it  is  calm  and  quiet;  respiration  is  slow 
and  the  beats  of  the  heart  augment  in  frequency.  Finally  the  ani- 
mal dies  from  an  affection  of  the  lungs  known  as  vagus  pneumonia. 


332  PHYSIOLOGY. 

For  a  time  after  the  section  the  amounts  of  carbonic  acid  exhaled  and 
of  oxygen  taken  in  remain  the  same,  but  finally  they  are  much 
changed.  The  animals  usually  live  seven  days,  but  Pawlow  has  suc- 
ceeded, by  dividing  one  vagus  and  then  waiting  some  time  before 
dividing  the  next  one,  in  keeping  them  alive. 

Instead  of  tying  or  dividing  the  vagi,  a  galvanic  current  may  be 
sent  through  them.  There  will  follow  disturbances  of  the  vascular 
system,  particularly  the  heart ;  so  that  death  follows  in  a  short  time. 
If  the  central  end  of  a  divided  vagus  be  irritated  by  a  strong  induc- 
tion current,  there  is  produced  a  strong  degree  of  excitation  in  the 
medulla  oblongata.  It  sends  out  impulses  along  motor  nerves  which 
arrest  respiration  in  a  state  of  inspiration,  due  to  tetanus  of  the  dia- 
phragm. Stimulation  of  the  central  end  of  the  superior  laryngeal 
calls  out  an  expiratory  arrest.     Each  half  of  the  respiratory  district, 


Fig.  134. — Arrest  of  Respiration  in  State  of  Expiration.      (Hedon.) 
By  irritation  of  the  central  end  of  the  vagus  in  a  chloralized  dog. 

termed  a  center,  consists  of  two  minor  centers,  which  are  in  an 
alternate  state  of  activity.  The  one  center  is  inspiratory ;  the 
other,  expiratory.  Each  one  forms  the  motor  central  point  for  the 
acts  of  inspiration  and  expiration.  The  co-ordinated  impulses  pro- 
ceed from  these  centers  in  the  medulla  along  the  nerves'  which  supply 
the  muscles  of  respiration  and  the  associated  muscles  of  the  face, 
nose,  and  larynx. 

The  activity  of  the  respiratory  center  is  excited  by  irritation  of 
the  sensory  nerves,  either  cutaneous  or  pulmonary.  It  may  also  be 
stimulated  by  the  accumulation  of  carbonic  acid  in  the  blood,  pro- 
ducing dyspnoea;  diminution  of  oxygen  and  the  presence  of  heat  are 
also  noticeable  factors.  According  to  some  observers,  the  acid  sub- 
stance formed  in  the  blood  when  the  muscles  are  greatly  exercised 
also  stimulates  the  inspiratory  center. 

The  functions  of  the  expiratory  center,  on  the  contrary,  are 
diminished  or  even  paralyzed  by  a  strong  excitation  of  the  sensory 


RESPIRATION.  333 

nerves.  Excess  of  oxygen  and  carbonic  acid  in  the  blood,  or  increased 
intracranial  pressure,  produce  similar  effects. 

The  consensus  of  opinion  among  physiologists  now  seems  to  be 
in  favor  of  considering  the  activities  of  the  respiratory  center  as 
partly  automatic,  partly  reflex,  and  that  the  vagus  is  the  principal 
nerve  concerned  in  the  reflex  activities. 

The  automatic  or,  according  to  Gad's  term,  the  "autoclhonic" 
irritation  of  the  respiration  center  is  due  to  the  blood-gases,  an  excess 
of  carbonic  acid,  and  possibly  a  deficiency  of  oxygen. 

Hering  and  Breuer  put  animals  in  a  state  of  apnoea  by  repeatedly 
filling  the  lungs  with  air  from  a  bellows.  Then  when  the  chest  was 
greatly  distended,  the  tracheal  cannula  was  closed  and  the  thorax  kept 
in  that  position.  The  first  movement  with  a  distended  chest  was  one 
of  expiration.  Then  after  the  animal  was  again  made  apnceic  by  re- 
peated insufflations,  the  air  was  sucked  out  of  the  chest,  the  tracheal 
cannula  closed,  and  the  chest  kept  in  that  position.  The  first  move- 
ment to  be  made  was  one  of  inspiration.  These  two  kinds  of  experi- 
ments show  that  dilatation  of  the  chest  irritates  the  fiber-ends  of  the 
vagus  in  the  lung,  which  carry  impulses  to  the  expiratory  center  to 
call  out  an  expiration.  The  collapse  of  the  lungs  shows  that  this  act 
excites  the  fiber-ends  of  the  vagus,  which  carry  impulses  to  the  in- 
spiratory center  to  call  out  an  inspiration.  Hence  the  knowledge  that 
in  the  vagus  we  have  fibers  of  two  kinds:  one  calling  out  expiration 
when  an  ordinary  inspiration  of  air  is  made,  the  other  calling  out 
inspiration  when  an  ordinary  expiration  is  made.  So  that  every  act 
of  inspiration  calls  out  an  expiration  and  every  act  of  expiration  calls 
out  an  inspiration. 

Apnoea. — When  a  dog  has  frequent  insufflations  of  air  through 
a  tracheal  cannula  by  means  of  a  bellows,  there  ensues  an  arrest  of 
respiratory  movements  for  a  short  time.  Rosenthal  believed  this  to 
be  due  to  an  excess  of  oxygen  in  the  blood  and  that  the  respiration 
centers  were  not  excited  because  of  this  excess  in  the  tissues.  Fred- 
ericque  lately,  by  cross-circulation  in  the  head  of  one  dog  with  blood 
from  another  dog,  has  been  able  to  produce  apnoea  which  remains  a 
long  time  if  the  other  dog  continues  to  receive  exaggerated  pulmonary 
insufflations.  This  apnoea  is  not  due  to  an  augmentation  of  the 
oxygen,  but  to  a  deficiency  of  carbonic  acid.  The  arrest  that  ensues 
in  a  dog  by  a  frequent  insufflation  of  hydrogen  instead  of  oxygen  is, 
according  to  Fredericque,  due  to  irritation  of  the  vagus  fibers,  which 
calls  out  an  expiration-arrest  and  which  is  a  simulated  apnoea. 


334 


PHYSIOLOGY. 


RESPIRATION.  335 

Asphyxia. — In  considering  the  phenomena  of  asphyxia,  it  is  nec- 
essary to  distinguish  between  rapid  asphyxia,  produced  by  complete 
obstruction  to  the  entrance  of  air,  and  slow  asphyxia,  which  is  grad- 
ually established.  The  phenomena  of  asphyxia  are  divisible  into 
three  stages,  which  are  easily  observed  in  animals,  especially  in  the 
dog. 

In  the  first  stage,  which  lasts  for  about  a  minute,  the  phenomena 
of  dyspnoea  appear  in  the  beginning,  the  forced  inspiratory  move- 
ments are  very  marked,  especially  for  the  thoracic  muscles;  the  ab- 
dominal muscles  then  contract  forcibly.  At  the  end  of  the  first  min- 
ute convulsions  appear,  which  at  first  are  purely  expiratory  and  after- 
ward accompanied  by  spasms,  more  or  less  irregular,  of  the  limbs, 
especially  of  the  flexor  muscles. 

In  the  second  stage,  which  lasts  about  the  same  length  of  time, 
the  convulsive  actions  cease,  sometimes  quite  suddenly;  the  expira- 
tory movements  at  the  same  time  are  scarcely  perceptible,  the  pupil 
is  dilated,  the  eyelids  do  not  close  when  the  cornea  is  touched,  reflex 
actions  have  ceased,  all  the  muscles  except  the  inspiratory  are  in  a 
state  of  relaxation,  the  arterial  pressure  is  elevated.  In  fact,  a  state 
of  general  calm  ensues,  which  contrasts  forcibly  with  the  agitation  of 
the  first  stage. 

In  the  third  stage,  which  lasts  from  two  to  three  minutes,  the 
inspiratory  movements  become  more  feeble  and  more  widely  separated, 
the  extraordinary  muscles  of  inspiration  contract  spasmodically, 
stretching  convulsions  ensue,  and  opisthotonos  is  present.  The  nos- 
trils are  dilated;  convulsive,  yawning  movements  take  place;  and 
death  closes  the  scene. 

The  phenomena  of  slow  asphyxiation  follow  the  same  course, 
but  with  less  rapidity. 

Circulatory  Effect  of  Asphyxia. — The  circulation  does  not 
change  until  the  second  period  of  asphyxia.  During  the  convulsive 
stage,  and  particularly  toward  its  close,  the  heart  enlarges  to  double 
its  former  dimensions.  This  enlargement  is  due  to  the  lengthening  of 
the  diastolic  interval  and  to  the  quantity  of  blood  contained  in  the 
great  veins,  which,  in  fact,  are  so  distended  that,  if  cut,  they  spurt 
like  an  artery.  The  arterial  pressure  at  first  rises  and  then  falls  from 
160  millimeters  to  20  millimeters.  These  changes  are  exjDlained  as 
follows :  The  increase  of  carbonic  acid  stimulates  the  vasoconstrictor 
center  and  thus  causes  general  contraction  of  the  arterioles.  The 
immediate  result  is  the  filling  of  the  venous  system,  in  the  production 
of  which  result  the  contraction  of  the  expiratory  muscles  of  the  trunk 


336  PHYSIOLOGY. 

and  extremities  co-operate  powerfully.  The  heart,  being  abundantly 
supplied  with  blood,  fills  rapidly  during  diastole  and  contracts  vigor- 
ously. In  consequence  of  these  conditions  and  the  vasomotor  con- 
striction, the  arterial  pressure  rises.  But  the  last  effect  is  only  tem- 
porary; the  diastolic  intervals  are  lengthened  from  the  excitation  of 
the  vagus  center  by  the  carbon  dioxide,  the  vasomotor  center  is  para- 
lyzed, and  the  weakness  of  the  heart  is  due  to  a  deficit  of  oxygen  in 
blood.  Then  the  heart  soon  passes  into  a  state  of  diastolic  relaxation 
and  greatly  enlarges.  Its  contractions  become  more  and  more  inef- 
fectual until  they  finally  cease,  leaving  the  arteries  empty,  the  veins 
full,  and  the  right  side  of  the  heart  engorged  with  blood. 

In  slow  asphyxia,  as  in  death  by  membranous  croup,  there  is  a 
feeling  of  painful  constriction  around  the  larynx  and  sternum,  yawns, 
gapings,  aiid  vain  efforts  to  breathe,  with  dimness  of  sight,  buzzing  in 
ears,  and  vertigo,  soon  followed  by  loss  of  consciousness.  The  face 
and  lips  are  tumefied  and  livid;  the  ej^cs  watery  and  projecting;  the 
conjunctiva  injected;  the  jugular  veins  distended  with  blood;  the 
nose,  ears,  hands,  and  feet  have  a  violet  color;  the  whole  skin  pre- 
sents spots  like  bruises;  the  heart  movements  are  uneven  and  inter- 
mittent, and  grow  weaker  and  weaker;  finally  the  respiratory  move- 
ments become  less  and  less  frequent,  soon  cease  altogether,  and  almost 
at  once  the  heart  stops  and  the  body  is  motionless  in  death. 

As  regards  mammals  particularly  the  age  affects  the  rapidity  of 
death  from  suffocation.  In  fact,  the  newborn  of  this  class  of  animals 
resist  the  suppression  of  respiration  very  much  longer  than  adults. 
This  accords  with  the  instances  of  newborn  infants  which,  having 
been  found  in  pools  of  water,  or  even  in  water-closets,  have  been  pre- 
served alive,  although  the  time  passed  since  their  immersion  permitted 
but  little  hope  of  saving  them.  An  adult  cannot  be  submerged  more 
than  four  minutes  and  live. 

Artificial  Eespiration  in  Asphyxia. — In  cases  of  suspended 
animation  artificial  respiration  must  be  performed.  Care  should  be 
taken  first  to  remove  any  foreign  bodies  or  froth  from  the  mouth  and 
nose.  Draw  forward  the  patient's  tongue  and  keep  it  projecting 
beyond  the  teeth.  Eemove  all  tight  clothing  from  about  the  neck  and 
chest.  For  relieving  asphyxia  by  dilating  and  compressing  the  chest 
so  as  to  cause  an  exchange  of  gases  there  are  several  methods.  Chief 
among  these  are  Sylvester's,  Marshall  Hall's  and  Schaefer's. 

In  the  Sylvester  method  the  tongue  is  pulled  forward  to  prevent 
any  hindrance  to  the  entrance  of  the  air  into  the  windpipe.  Expan- 
sion of  the  chest  is  produced  by  drawing  the  arms  from  the  sides  of 


RESPIRATION. 


337 


the  body  and  then  upward  until  they  almost  meet  over  the  head. 
Bringing  the  arms  down  to  the  sides  again,  causing  the  elbows 
almost  to  meet  over  the  pit  of  the  stomach,  produces  contraction  of 
the  chest.  The  rate  of  elevation  and  depression  of  the  arms  should 
be  about  sixteen  times  per  minute. 

In  the  j\Iarshall  Hall  method  the  person  is  placed  flat  upon  his 
face,  gentle  intermittent  pressure  being  made  upon  the  back  with  one's 
hands.  The  body  is  then  turned  on  the  side  and  a  little  beyond,  then 
upon  the  face  again,  and  the  same  pressure  continued  as  at  first.  The 
entire  body  must  be  worked  simultaneously,  the  same  number  and 
frequency  of  these  artificial  processes  of  respiration  being  employed 
as  in  the  Sylvester  method. 


Fig.  13G. — Shows  tlie  Position  to  be  Adopted  for  Effecting  Artificial 
Respiration  in  Cases  of  Drowning.      (Schaefee,  Howell.) 

Schaefer  describes  a  new  method  of  artificial  respiration.  It 
consists  in  laying  the  subject  in  the  prone  posture,  preferably  on  the 
ground,  with  a  thick,  folded  garment  underneath  the  chest  and  epi- 
gastrium. The  operator  puts  himself  athwart  or  at  the  side  of  the 
subject,  facing  his  head,  and  places  his  hands  on  each  side  over  the 
lower  part  of  the  back  (lowest  ribs).  He  then  slowly  throws  the 
weight  of  his  body  forward  to  bear  upon  his  own  arms  and  thus 
presses  upon  the  thorax  of  the  subject  and  forces  air  out  of  the  lungs. 
This  being  effected,  he  gradually  relaxes  the  pressure  by  bringing  his 
own  body  up  again  to  a  more  erect  position,  but  without  moving  his 
hands.  Efforts  should  be  continued  for  a  half  hour  before  acknow- 
ledging failure  to  restore  life. 

Ploman^  has  made  many  experiments  upon  men  in  a  study  of  the 


^  SkandinavLsches   Archiv,    1906. 


22 


338  PHYSIOLOGY. 

various  methods  of  artificial  respiration.  He  used  Gad's  aeroplethys- 
mograph  to  measure  the  volume  of  the  ingoing  and  outgoing  air.  He 
found  that  the  usual  methods  of  Hall,  of  Howard,  and  of  Sylvester 
produced  a  ventilation  of  the  lungs  much  greater  than  is  normally 
accomplished.  The  Schaefer  method  gave  a  ventilation  a  little 
greater  than  that  of  normal  breathing.  He  believes  the  Sylvester 
method  to  be  best  for  artificial  respiration,  especially  when  carried 
on  with  the  modification  of  D'Jelitzin. 

D'Jelitzen  proceeded  as  follows :  At  the  same  time  that  the  arms 
are  carried  upward  in  the  direction  of  the  long  axis  of  the  body, 
the  grip  is  transferred  from  the  forearms  to  the  elbows,  so  that  the 
elbows  strike  against  each  other  above  the  nape  of  the  neck,  or  above 
the  throat.  In  producing  an  expiration,  the  elbows  are  brought 
against  the  chest  by  the  side  of  the  sternum,  and  pressure  made  from 
before  backwards. 

In  the  Laborde  method  rhythmical  traction  of  the  tongue  is 
made.     This  acts  in  a  reflex  way  on  the  center  of  respiration. 

In  artificial  respiration  a  bellows  may  be  employed  in  a  gentle 
manner  so  as  not  to  rupture  the  lung. 

Modified  Respiratory  Movements. — Since  to  breathe  is  to  live, 
the  modes  of  breathing  indicate  the  modes  of  life.  We  see  unfolded 
in  a  series  of  modifications  of  the  respiratory  act  many  of  the  sensa- 
tions and  emotions  which  man  experiences  in  the  course  of  his  exist- 
ence. His  birth  is  announced  by  a  cry,  which  seems  the  expression  of 
a  first  pain;  his  death  is  revealed  by  a  sigh,  in  which  his  last  suffer- 
ing is  breathed  out.  In  the  number  of  his  days  there  are  very  few 
devoted  to  laughter.  There  are  more  for  sobs.  Yawning  often  ex- 
presses his  weariness;  straining,  the  severity  of  his  labor;  sneezing, 
coughing,  and  expectoration  are  so  many  means  that  Nature  employs 
to  struggle  against  uncomfortable  or  painful  sensations.  All  of 
these  result  from  modifications  of  respiration.  Hiccough  is  only 
manifested  with  their  aid.  Voice  or  speech,  the  supreme  attribute  of 
man,  is  only  a  particular  mode  of  respiration. 

Sighing. — A  large  inspiration,  slowly  executed  and  followed  by  a 
rapid  and  sonorous  expiration,  constitutes  the  sigh.  In  normal  condi- 
tions of  respiration,  in  about  every  five  or  six  inspirations  there  is  one 
which  is  longer  than  the  others;  it  is  really  a  slight  sigh.  It  is  sup- 
posed that  this  longer  inspiration  supervenes  whenever  oxidation  of 
blood  needs  to  be  accelerated.  It  takes  place  without  participation  of 
the  will;  in  fact,  it  is  one  of  those  movements  called  reflex.  The 
nervous  center  reacts  spontaneously  by  reason  of  a  painful  impression 


RESPIRATION.  339 

received,  because  of  the  accumulation  of  the  venous  blood  in  the  right 
cavities  of  the  heart.  The  unpleasant  effect  of  sad  emotions  upon 
oxidation  of  the  blood  explains  why  sighs  are  given  at  such  times. 
Their  contagious  nature  is  due  entirely  to  sympathy. 

The  Yawn  differs  from  the  sigh  more  by  its  mechanism  than 
by  its  causes  or  effects.  The  needs  of  oxidation  of  blood  call  it  forth 
in  the  same  manner  as  the  sigh  is  elicited.  But,  whereas  the  sigh  may 
be  voluntary,  the  yawn  is  always  involuntary.  It  is  not  easy  of  imita- 
tion, since  it  is  purely  reflex;  a  person  usually  will  not  yawn  if  the 
need  of  doing  it  does  not  exist.  Besides  its  relation  to  oxidation,  it 
also  expresses  painful  sensations  in  the  stomach,  hunger,  or  a  feeling 
of  torpor  at  the  approach  of  sleep. 

The  Hiccough  cannot  be  compared  with  the  acts  connected  with 
respiration,  except  by  the  noise  accompanying  it.  It  is  a  spasmodic 
contraction,  abrupt  and  involuntary,  of  the  diaphragm  with  coincident 
contraction  of  the  glottis.  The  air,  drawn  rapidly  into  the  chest  by 
the  convulsive  contraction  of  the  diaphragm,  breaks  upon  the  out- 
stretched lips  of  the  glottis,  where  is  produced  the  sound  characteris- 
tic of  hiccough.  The  ordinary  causes  for  this  phenomena  are  en- 
gendered in  the  stomach  by  the  too  rapid  introduction  of  alimentary 
substances,  by  alcoholic  drinks  or  those  charged  with  carbonic  acid, 
and  by  certain  foods.  It  can  also  result  from  a  special  state  of  the 
nervous  centers. 

Coughing  usually  arises  from  an  irritation  in  the  laryngeal  pas- 
sage ;  the  irritating  effect  of  the  sensory  filaments  of  the  larynx 
reaches  a  certain  intensity ;  there  is  then  a  deep  inspiration,  which  is 
followed  by  a  sudden  and  strong  expiration. 

Coughing  can  l)e  produced  voluntarily,  but  it  is  more  often 
caused  by  reflex  action,  which  it  is  generally  impossible  to  resist.  A 
cold  draught  on  the  skin  or  a  tickling  of  the  external  auditory  meatus 
will  provoke  a  cough  in  some  people. 

Laughing  and  Sobbing  have  this  feature  in  common :  they  have 
their  seat  in  the  chest  and  face  at  the  same  time.  They  act  especially 
upon  the  same  muscle:  the  diaphragm.  In  the  face  they  differ  in 
this,  that  one  has  its  own  particular  seat  in  the  region  of  the  eye,  the 
other  around  the  mouth.  The  same  muscles,  the  same  nerves,  pro- 
duce sobs  and  laughter.  Their  movements  of  inspiration  and  expira- 
tion are,  however,  accompanied  by  their  own  characteristic  sounds. 

Snoring  is  due  to  vibration  of  the  soft  palate. 

Cheyne-Stokes  Eespiration. — This  is  a  peculiar  modification 
of  the  respiratory  movements  which  is  seen  in  certain  pathological 


340  PHYSIOLOGY. 

conditions,  as  in  fatty  heart,  atheroma  of  the  aorta,  certain  apoplex- 
ies, and  in  ura?niia.  It  has  even  been  noted  in  healthy  children  dur- 
ing sleep.  It  consists  of  respiratory  pauses  alternating  with  a  series 
of  respirations  till  a  maximum  depth  and  rapidity  is  reached;  after 
this  climax  they  gradually  diminish  till  they  end  in  another  pause. 
Certain  drugs — chloral  is  one — may  cause  Cheyne-Stokes  respiration. 

Cheyne-Stokes  respiration  rhythm  is  to  the  respiratory  system 
what  the  Traube-Hering  rhythm  is  to  the  circulatory  system.  Both 
arise  in  their  respective  centers  in  the  medulla  oblongata. 

The  pause  in  Cheyne-Stokes  respiration  is  somewhat  less  than 
half  of  the  duration  of  the  active  period.  During  the  pause  the 
pupils  are  contracted  and  inactive;  when  respiration  begins  again 
they  become  dilated  and  sensitive  to  light.  The  eyeball  is  usually 
moved  at  the  same  time. 


Fig.    137. — Cheyne-Stokes  Respiration.     (Waller.) 

CHEMISTRY  OF  RESPIRATION. 

Looked  at  from  a  chemical  point  of  view,  respiration  presents 
the  following  phenomena:  (1)  absorption  of  oxygen;  (2)  exhalation 
of  carbon  dioxide;  (3)  release  of  a  certain  quantity  of  nitrogen;  (4) 
exhalation  of  vapor  of  water. 

It  has  been  previously  stated  that  at  each  normal  respiration 
of  atmospheric  air  but  one-sixth  of  the  air  within  the  lungs  is 
changed.  This  current  does  not  actually  penetrate  beyond  the  largest 
bronchial  tubes.  The  air  which  finds  its  way  into  the  bronchioles  and 
air-vesicles  does  so  hy  diffusion. 

The  student  has  already  learned  that  the  normal  lung  contains 
within  it  a  certain  quantity  of  air  which  cannot  be  expelled  by  the 
strongest  expiration :  residual  air.  This  air  is  contained  within  the 
alveolar  air-spaces;  its  exchange  with  the  atmospheric  air  is  accom- 
plished by  the  slower  processes  of  gaseous  diffusion.     The  difference 


RESPIRATION. 


341 


in  the  amount  and  pressure 
of  the  two  gases — oxygen 
and  carbonic-acid  gas — is 
the  real  explanation  of  the 
current-movement  of  the 
two.  The  CO2  moves  out- 
ward, the  0  inward.  The 
interchange  is  aided  by 
the  heart-movements,  also. 
When  the  heart  contracts 
(systole)  it  occupies  less 
space  in  the  thorax  than  it 
does  during  relaxation  (dia- 
stole). Hence,  air  is  sucked 
in  or  pushed  outward 
through  the  open  glottis  by 
these  movements. 

A  glance  at  the  anat- 
omy of  lung-structure  re- 
veals the  fact  that  the  alve- 
oli are  surrounded  by  a 
dense  network  of  capil- 
laries. Some  of  the  capil- 
laries even  project  into  the 
air-spaces.  These  condi- 
tions make  more  easy  the 
processes   of  diifusion. 

Some  of  the  oxygen 
from  the  respired  air  passes 
into  the  blood  to  form  a 
loose  chemical  combination 
with  the  hffimoglobin  of  the 
red  corpuscles :  oxyhsemo- 
globin.  This  gives  to  the 
blood  its  red  color,  mak- 
ing it  arterial.  At  the 
same  time  there  is  diffusion 
of  carbonic  acid  from 
the  impure,  venous  blood 
into  the  alveolar  com- 
partments.    Gradually  it  rises  in  the  air-vesicles  and  bronchioles 


Fig.   138. — Ludwig's  Mercurial  Air  Pump  to 
Extract  Blood  Gases.      (Lahousse.) 
G,   Receptacle  for  the  blood. 


342 


PHYSIOLOGY. 


until  it  finds  its  way  into  the  current  of  air  in  the  larger  bronchioles, 
by  which  it  is  expelled  from  the  system.  With  this  rise  of  carbonic 
acid  in  the  alveolar  air  there  is  a  corresponding  descent  of  oxygen 
for  purposes  of  oxygenation.  The  oxyhsemoglobin  of  the  blood  is 
carried  along  by  the  blood-stream  to  the  tissues  (the  real  seats  of 
respiration),  where  it  becomes  disengaged  to  unite  with  the  tissue- 
cells.  In  the  production  of  heat  and  energy  it  has  united  with  the 
carbon  of  the  tissues  to  form  carbonic  acid  and  with  the  hydrogen 
to  form  water.  That  which  is  not  used  up  at  once  constitutes  a 
reserve  supply  in  the  tissue  to  be  used  as  occasion  demands. 


Fig.  139. — Schema  of  the  Large  Respiration  Apparatus  of 
Pettenkofer.      (Fredericque.) 

A,  Chief  current  of  air  measured  by  the  meter,  but  not  analyzed.  B,  Portion 
of  air  analyzed  and  coming  from  the  chief  current  of  air.  C,  Portion  of  air 
analyzed  and  coming  from  the  surrounding  air  before  it  enters  the  apparatus. 


It  has  been  ascertained  that  the  quantity  of  oxygen  absorbed 
within  a  given  time  is  not  found  entirely  in  the  carbonic  acid  exhaled 
by  the  animal  during  the  same  time.  Consequently  one  can  scarcely 
consider  the  oxygen  as  employed  solely  in  burning  carbon  or  in  form- 
ing carbonic  acid.  Thus,  animals  draw  from  the  surrounding  atmos- 
pheric medium  a  quantity  of  free  oxygen  which  attacks  the  ternary 
and  quaternary  materials  of  the  organisms.  These  then  exhale  car- 
bonic acid  and  water  as  the  result  of  the  respiratory  combustion, 
together  with  a  small  quantity  of  nitrogen.     The  latter  proceeds 


RESPIRATION.  343 

from  the  destruction  of  a  certain  proportion  of  the  nitrogenized  sub- 
stances of  the  blood  and  tissues.  As  an  animal  can  keep  its  weight 
the  same  during  these  combustive  changes,  it  must  be  admitted  that 
the  carbon,  hydrogen,  and  nitrogen  thus  lost  must  be  unceasingly 
renewed  by  the  food  it  ingests  and  digests. 

It  is  impossible  to  observe  any  constancy  in  the  quantity  of  the 
products  consumed  or  exhaled  while  searching  into  the  amounts  of 
oxygen  absorbed  and  carbonic  acid  given  off  by  man  in  a  certain 
time.  The  chemical  phenomena  of  respiration  are,  in  fact,  of  such 
extreme  changeableness,  due  to  the  variety  of  causes,  that  physiol- 
ogists can  scarcely  know  them  all. 

The.  expired  air  is  richer  in  COj  than  inspired.  It  contains  4.38 
volumes  per  cent,  of  this  gas,  and  consequently  a  hundred  times 
more  CO.  than  the  air  inspired. 


Air  Inspired.    Az— Nitrogen.  Air  Expired.    Az— Nitrogen. 

Fig.  140. —  (Langlois.) 

The  air  expired  is  poorer  in  oxygen.  It  contains  16.03  volumes 
per  cent,  of  this  gas,  which  is  about  -i.78  volumes  per  cent,  less  than 
the  inspired  air.  These  figures  show  that  the  absorption  or  loss  of 
oxygen  is  greater  than  the  elimination  of  COo.  This  further  sub- 
stantiates the  statement  that  all  of  the  oxygen  absorbed  does  not 
appear  in  the  form  of  carbonic  acid. 

80  often  in  the  study  of  physiology  the  student's  attention  is 
called  to  the  fact  that  the  movements  of  the  fluids  of  the  body  are 
always  in  the  direction  of  the  higher  to  lower  pressure.  The 
explanation  of  the  exchange  of  gases  held  in  loose  combination  in 
the  blood  and  those  comprising  the  atmospheric  air  in  the  lungs  is 
another  interesting  study  of  difference  of  pressure. 

The  exchange  depends  upon  the  law  of  "dissociation  of  gases," 
and  is  as  follows:  "Many  gases  form  true  chemical  compounds  with 
other  bodies  when  the  contact  of  these  bodies  is  effected  under  such 
conditions  that  the  partial  pressure  of  the  gases  is  high.     The  chem- 


344  PHYSIOLOGY. 

ical  compound  formed  under  these  conditions  is  broken  up  whenever 
the  partial  pressure  is  diminished,  or  when  it  reaches  a  certain  mini- 
mum level,  which  varies  with  the  nature  of  the  bodies  forming  the 
compound.  Thus,  by  alternately  increasing  and  decreasing  the  par- 
tial pressure,  a  chemical  compound  of  the  gas  may  "be  formed  and 
again  broken  up."     (Landois). 

The  CO,  and  the  0  in  the  blood  form  certain  loose  combinations 
which  follow  this  law  exactly.  These  gaseous  'compounds,  as  they 
circulate  with  the  blood-stream,  find  conditions  of  high  and  low  pres- 
sure enveloping  them,  whence  they  take  up  and  give  off  their  respec- 
tive gases.  As  the  pressures  vary,  so  does  the  dissociation  of  the 
gases  vary. 

Thus,  the  oxygen-carrying  element  of  the  blood,  the  haemoglobin 
of  the  red  corpuscles,  as  it  reaches  the  pulmonary  capillaries  is  poor 
in  0.  The  air  adjoining  these  cells  in  the  pulmonary  alveoli  is  rich 
with  0.  The  low-pressure  hgemoglobin  unites  with  the  high-pres- 
sue  0  to  form  the  loose  compound  oxyhsemoglobin.  Later,  the  oxy- 
hsemoglobin  meets  with  tissues  poor  in  oxygen  and  in  need  of  this 
element  for  their  combustion.  There  is  a  dissociation  from  a  higher 
to  a  lower  pressure  whereby  the  tissues  receive  their  needed  supply. 
The  corpuscles  must  needs  receive  replenishment  again  from  the 
alveolar  oxygen,  and  in  this  way  the  circle  is  completed. 

On  the  other  hand,  the  blood  in  contact  with  the  body-tissues 
meets  a  high  pressure  of  COo.  By  reason  of  which  compounds  are 
formed  containing  COg,  in  which  form  they  reach  the  air-vesicles  in 
the  lungs.  The  inspired  air  contained  within  the  air-vesicles  has  a 
much  lower  pressure  of  COo  than  that  contained  in  the  venous  blood 
coming  from  the  tissues.  Hence,  the  dissociation  of  the  CO2  from 
the  blood  into  the  vesicular  air,  finally  to  make  its  exit  along  the 
bronchioles,  bronchi,  trachea,  etc.,  to  the  atmosphere.  Bohr,  of 
Copenhagen,  believes  the  epithelial  cells  of  the  air-cells  have  the 
power  to  excrete  carbonic  acid  and  to  absorb  oxj^gen  independent  of 
the  differences  in  tension  of  the  gases. 

Bohr  has  also  shown  that  the  vagi  have  an  influence  upon  the 
intake  of  oxygen  and  the  out-take  of  carbonic  acid.  In  the  turtle, 
section  of  a  vagus  was  followed  by  a  considerable  fall  in  the  absorp- 
tion of  oxygen.  Irritation  of  the  vagus  increased  the  absorption  of 
oxygen.  In  the  warm-blooded  animal  irritation  of  the  vagus  in- 
creased the  absorption  of  oxygen  and  the  exhalation  of  carbonic  acid. 

Seat  of  Oxidation. — It  used  to  be  held  that  the  lungs  were  the 
seat  of  the  metabolic  processes.     Afterwards  the  seat  of  these  chem- 


RESPIRATION.  345 

ical  changes  was  located  in  the  tissues,  the  lungs  playing  but  a  small 
part.  Bohr  has  shown  that  about  one-third  of  the  metabolic  phe- 
nomena take  place  in  the  lung.  He  estimated  the  carbonic  acid  and 
oxygen  in  the  blood  of  the  right  heart,  and  compared  these  quantities 
with  those  found  in  the  blood  of  the  left  heart.  He  also  measured 
the  quantity  of  blood  passing  through  the  lungs  in  a  given  time. 
Knowing  the  amount  of  oxygen  inhaled  and  the  quantity  of  carbon 
dioxide  exhaled,  he  found  that  the  lungs  used  up  about  one-third  of 
the  oxygen  and  gave  off  one-third  of  the  total  carbon  dioxide  output. 
The  temperature  of  the  air  expired  is  greater  than  that  of  the 
air  inspired,  and  is  but  a  trifle  lower  than  the  body-temperature. 
Though  the  temperature  of  the  surrounding  atmosphere  varies,  that 
of  the  expired  air  remains  nearly  the  same. 


Proteids.  Normal  P'ood  Supply. 

Fig.    141. — Variations  of  Respiratory  Quotient  According  to   Food 
Taken.     (  Langlois.  ) 

The  volume  of  the  air  expired  is  greater  than  the  volume  of  the 
air  inspired,  by  reason  of  the  increase  in  temperature  and  the  con- 
tained watery  vapor.  If,  however,  it  be  dried  and  reduced  to  the 
same  temperature  as  the  inspired  air,  there  will  be  a  diminution  of 
volume:    about  one-fiftieth. 

The  respiratory  quotient  is  the  relation  between  the  volume 
of  oxygen  absorbed  and  the  volume  of  carbonic  acid  eliminated. 
That  is:— 

volume  of  COo  given  off 

The  respiratory  quotient  = .     Normally  it  is 

volume  of  0  absorbed 

•4.38 

about       -=0.9. 

4.78 

This  quotient  varies,  however,  with  the  nature  of  the  chemical 

composition   of   the    foods    ingested.     With    the    hydrocarbons    the 

quotient   approaches   unity.     The    carbohydrates   contain    in    their 


346 


PHYSIOLOGY. 


molecules  enough  oxygen  to  oxidize  their  hydrogen;  all  that  remains 
for  the  inspired  oxygen  is  to  burn  up  the  carbon.  The  tats  and 
albumins,  on  the  contrary,  possess  too  little  oxygen  to  burn  all  of 
the  hydrogen  and  nitrogen  they  contain.  Hence  all  of  the  oxygen 
is  not  found  in  the  COo  eliminated,  and  the  respiratory  quotient  falls 
to  0.75.  On  a  mixed  diet  the  quotient  is  intermediate  between  0.9 
and  0.75.  In  plants  the  respiratory  quotient,  especially  in  starchy 
ones,  is  equal  to  1.0.  In  fatty  seeds  the  respiratory  quotient  is 
0.6  to  0.8. 

Muscular  activity  augments  the  gaseous  exchanges  and  so  makes 
the  respiratory  quotient  approach  a  unit.  All  things  being  equal, 
man  absorbs  more  oxygen  and  exhales  more  carbonic  acid  than  a 
woman.     The  exchanges  are  increased  during  pregnancy. 


Carbohydrates.  Fats. 

Fig.    142. — Variations  of  Respiratory  Quotient  According  to   the 
Food  Taken.      (Langlois.  ) 

During  sleep  the  consumption  of  oxygen  and  the  elimination  of 
COo  diminish  about  one-fourth.  This  decrease  depends  upon  mus- 
cular and  intellectual  repose,  darkness,  etc.  The  cells  of  the  tissues 
determine  the  amount  of  oxygen  needed,  and  not  an  excess  of  the 
oxygen  present.  The  intramolecular  changes  take  place  in  the  cells 
of  the  tissue,  and  not  in  the  blood.  The  amount  of  water  thrown 
off  daily  is  about  a  pound;  of  oxygen  taken  in,  about  a  pound  and 
one-half;  and  of  carbonic  acid  thrown  off,  a  little  more  than  a  pound 
and  a  half. 

In  human  blood  the  average  total  gases  are  estimated  to  be,  in 
round  numbers,  60  volumes  per  cent,  at  0°  C.  and  760  millimeters' 
pressure,  made  up  as  follows: — 

Arterial,  Venous 

Blood.  Blood. 

Oxygen 20  8  to  12 

Nitrogen 1.4  1.4 

Carbonic  acid 39  46 


RESPIRATION. 


347 


The  above  table  represents  the  average  composition  of  the  gases 
contained  in  man's  blood. 

A  considerable  attraction  exists  between  the  particles  of  solid, 
porous  bodies  and  gases,  whereby  the  latter  are  condensed  within  the 
pores  of  the  solid  bodies;  that  is,  the  gases  are  absorbed.  Fluids 
also  can  absorb  gases.  One  of  the  functions  of  the  blood  is  to  carry 
oxygen  from  the  lungs  to  the  tissues  and  carbon  dioxide  from  the 
tissues  back  to  the  lungs  for  expulsion  from  the  economy.  These 
two  gases,  together  with  nitrogen,  present  themselves  in  two  differ- 
ent states  in  the  blood.  The  blood,  a  fluid,  must  very  naturally 
absorb  gases  also.  Hence  one  would  expect  to  find  0,  CO.,  and  N 
held  in  solution,  and  also  that  these  gases  should  behave  according 
to  Dalton's  law:   the  amount  of  gas  dissolved  in  a  liquid  varies  with 


A. — Arterial  blood  per  100. 

0 33 

CO2 64 

Af 3 

100 


T. — Venous  blood  per  100. 

0 14 

CO2 83 

N 3 

100 


Az   is   nitrogen. 
Fig.    14.3. — Relative  Proportion  of  Gases  of  Blood.      (Laxglois.) 

the  pressure  of  the  gas;  the  higher  the  pressure,  the  greater  the 
amount  of  gas  dissolved.  But  oxygen  held  in  the  blood  disregards 
Dalton's  law,  since  its  proportions  in  the  blood  in  various  parts  of 
the  body  remain  fairly  constant  no  matter  what  the  pressure. 
Hence,  it  owes  its  presence  in  and  obeys  laws  dependent  upon  its 
being  in  the  form  of  loose  chemical  combinations.  If  the  oxygen 
were  mainly  held  in  solution,  then  the  blood  would  give  it  up  in  a 
forming  vacuum  in  direct  proportion  to  the  falling  oxygen-pressure. 
That  these  conditions  do  not  follow  tends  to  establish  the  fact  that 
the  oxygen  is  held  by  some  cJiemiral  union.  Experimental  physiol- 
ogists also  tell  us  that  in  their  work  they  notice  that  very  little  0 
is  given  off  in  a  forming  vacuum  until  a  very  much  reduced  pres- 
sure is  reached,  when  there  is  a  sudden  evolution  of  the  gas,  just 
as  though  it  had  been  freed  from  some  restraining  influence.     The 


348  PHYSIOLOGY. 

restraint  is  now  generally  accepted  to  be  the  chemical  union  before 
mentioned. 

Physiologists  admit  to-day  that  the  major  portion  of  the  oxygen 
of  the  blood  is  contained  in  the  red  corpuscles,  which  are  the  special 
messengers  for  carrying  it  to  the  different  tissues.  Their  capacity 
for  holding  oxygen  is  nicely  demonstrated  by  the  following  simple 
experiment:  Serum,  without  corpuscles,  is  agitated  in  the  presence 
of  oxygen.  The  amount  of  oxygen  absorbed  is  found  to  be  less  than 
half  what  would  l)e  taken  up  l)y  the  same  amount  of  serum  contain- 
ing red  corpuscles. 

The  oxygen,  being  preferably  united  with  the  corpuscles,  is 
joined  to  them  in  a  very  unstable  combination.  The  affinity  is  just 
strong  enough  to  facilitate  the  conveyance  of  the  gas  in  the  circula- 
tory system,  yet  not  so  strong  but  that  it  niay  attack  tlie  combustible 
materials  of  the  tissues.  Oxygen  united  chemically  with  haemo- 
globin forms  oxyha^.moglobin. 

However,  it  must  be  kept  in  mind  that  some  of  the  oxygen  is 
contained  in  the  hlood-plasma,  where  it  is  in  simple  solution  and 
obeys  the  laws  of  Dalton. 

There  can  scarcely  be  any  doubt  of  the  source  of  the  oxygen 
contained  in  the  blood,  for  it  evidently  comes  from  the  atmospheric 
air,  of  which  it  forms  one  of  the  elements.  It  represents  the  indis- 
pensable agent  of  most  of  the  transformations  which  take  place  in 
the  heart  of  the  general  economy. 

Ehrlich  injected  methylene  blue  into  the  vein  during  life. 
After  death  the  blood  was  found  to  be  blue  in  color,  and  the  other 
tissues,  especially  the  glandular,  to  be  without  color.  Here  the 
avidity  of  the  tissues  for  oxygen  has  removed  this  from  the  methy- 
lene blue,  which  then  becomes  colorless.  After  a  time  the  oxygen 
in  the  air  is  absorbed  and  methylene  blue  is  again  formed. 

A  curious  phenomenon  of  respiration  in  the  tissues  is  that  the 
exhalation  of  carbon  dioxide  does  not  directly  depend  upon  the  pres- 
ence of  oxygen.  For  fragments  of  tissue,  when  placed  in  an  atmos- 
phere absolutely  deprived  of  oxygen,  as  in  hydrogen,  continue  to 
produce  carbonic  acid.  Hermann  has  supposed  that  a  substance, 
inogen,  exists  in  muscular  tissue  which  condenses  some  oxygen, 
which  is  disengaged  according  to  the  needs  of  the  tissue.  Eespira- 
tion  is  not  so  simple  as  it  appears  to  be :  the  oxygen  absorbed  is  not 
immediately  transformed  into  carbonic  acid. 

The    cells   of    the    tissues    determine    the   amount    of    oxygen 


RESPIRATION.  349 

required,  and  not  the  amount  of  oxygen  available.  Inhalations  of 
pure  oxygen  do  not  augment  the  oxidation  in  the  tissues. 

The  intracellular  ferments  change  and  oxidize  the  dead  food- 
materials  in  the  extracellular  lymph  which  bathes  them,  just  as  has 
been  shown  that  the  yeast-cells  break  up  the  sugar  surrounding  them 
by  their  intracellular  ferment,  zymase,  forming  carbonic  acid  and 
alcohol.  The  animal  tissues  are  like  the  yeast-cell,  which  obtains 
its  oxygen,  when  deprived  of  it,  by  taking  oxygen  from  that  con- 
tained in  the  sugar,  for  the  animal  tissues  are  anaerobic,  as  they 
obtain  the  oxygen  from  the  combined  haemoglobin.  If  living  tissue 
is  removed  from  the  body  and  kept  warm,  moist,  and  aseptic,  it 
breaks  up  by  hydrolytic  cleavage  into  simpler  compounds.  Just  as 
the  tissue  does  when  boiled  with  acids.  This  action  is  called  auto- 
lysis, and  is  due  to  intracellular  ferments.  Pasteur  holds  that  fer- 
mentation is  a  general  phenomenon  in  metabolism.  Schmiedeberg 
and  others  have  shown  a  great  number  of  oxidations  taking  place 
in  the  body  which  can  only  ensue  through  the  intervention  of  intra- 
cellular ferments,  which  are  called  oxidases. 

About  one-third  of  the  carbonic  acid  in  the  blood  is  found 
united  with  the  globin  of  the  red  corpuscles,  whilst  the  oxygen  is 
combined  with  the  iron-holding  part  of  the  blood. 

The  tension  of  the  carbonic  acid  in  the  tissues  is  high.  It  is 
less  in  the  alveolar  air.  Hence  we  find  it  working  its  way  along  the 
respiratory  passages  to  be  expelled  by  the  movements  of  respiration. 
The  movement  of  the  oxygen  was  found  to  be  toward  the  tissues; 
the  direction  of  carbon  dioxide  is  the  reverse:  away  from  the  seats 
of  tissue-combustion. 

Nitrogen. — The  blood  absorbs  more  nitrogen  than  the  same 
volume  of  water  would  under  the  same  condition.  The  increased 
absorption  of  nitrogen  is  dependent  upon  some  physical  conditions 
of  the  blood.     These  are  the  presence  of  hsemoglobin  and  oxygen. 

Relation  of  CO2  in  the  Blood. — Carbonic  acid  must  be  regarded, 
on  the  contrary,  as  one  of  the  final  products  of  the  nutritive  trans- 
mutations. It  is  destined  to  be  eliminated  with  the  vapor  of 
water  and  free  nitrogen,  especially  through  the  respiratory  passages. 
When  the  very  small  proportion  of  this  gas  in  ordinary  atmospheric 
air  and  its  considerable  amount  in  expired  air  are  considered,  it  is 
easy  to  be  convinced  that  carbonic  acid  is  indeed  a  product  of  the 
organism.  The  gas,  therefore,  comes  from  the  tissues  and  liquids 
themselves  of  animals,  and  not  from  outside  media. 

It  is  very  generally  admitted  that  the  greater  part  of  the  car- 


350  PHYSIOLOGY. 

bonic  acid  is  in  a  condition  of  chemical  combination.  The  principal 
compoimd  is  bicarbonate  of  sodium,  in  the  serum. 

The  sodium  in  the  blood  is  the  seat  of  a  constant  struggle 
between  the  carbonic  and  phosphoric  acids  to  form  a  combination 
with  it.  When  carbonic  acid  is  in  excess,  there  results  sodium  car- 
bonate and  monosodium  phosphate.  When  the  carbonic  acid  is 
diminished,  the  phosphoric  acid  acquires  the  greater  part  of  the 
sodium,  to  form  disodium  phosphate. 

It  has  been  found  that,  when  the  lung  is  distended,  the  heart 
beats  faster;  this  increased  action  is  caused  by  an  irritation  of  the 
sensory  nerves  in  the  lungs,  which,  in  a  reflex  manner,  inhibits  the 
cardio-inhibitory  center  and  permits  the  heart  to  beat  faster  as  the 
brake  is  taken  off. 

Dr.  Da  Costa,  in  his  examination  of  twenty-four  glass-blowers, 
found  that  in  eleven  the  pulse  ranged  from  90  to  116  per  minute.  I 
have  shown  elsewhere  that  this  is  due  to  the  irritation  of  the  sensory 
fibers  of  the  vagus  by  the  great  distension  of  the  lungs,  which  also 
diminishes  the  irritability  of  the  cardio-inhibitory  center.  The 
great  lung-distension  in  glass-blowers  occurs  daily  for  years. 

Now,  it  is  well  known  that  the  inhibitory  power  of  tlie  vagus  in 
man  is  very  great,  and  its  power  varies  in  different  individuals;  this 
would  explain  why  the  thirteen  other  glass-blowers  showed  no  habitual 
acceleration  of  the  heart.  As  this  performance  is  kept  up  many 
hours  daily  for  a  series  of  years,  it  is  easy  to  conceive  that  the  cardio- 
inhibitory  power  of  the  vagus  centers  receives  such  a  diminution  of 
irritability  so  often  that  it  would  at  length  remain  constantly  weak. 

The  vasomotor  center  also  sends  out  rhythmical  impulses  by 
which  undulations  of  blood-pressure  are  produced.  That  this  cen- 
ter is  capable  of  producing  such  undulations  has  been  amply  verified 
by  the  existence  of  the  Traube-IIering  curves. 

Respiration  of  Different  Gases. — Eespiration  is  essentially  the 
intake  of  oxygen  and  the  output  of  carbon  dioxide  by  the  living  cells. 
Among  the  higher  orders  of  animals  two  phases  of  respiration  are 
distinguished — the  external,  the  exchange  of  gases  between  the  air 
or  water  and  the  blood;  and  the  internal,  the  exchange  between  the 
blood,  lymph,  and  the  tissues. 

The  usual  and  normal  medium  inspired  is  ordinary  atmospheric 
air,  from  which  there  is  derived  the  needful  supply  of  oxygen.  The 
open  atmosphere  is  a  mixture  of  gases  in  the  following  approximate 
proportions : — 


RESPIRATION.  351 

f   Nitrogen,  including  argon,  etc 79.00  "\ 

Atmosphere        Oxygen  20.96  v  in  100  parts. 

(    Carbon  dioxide 0.04  j 

Argon,  NH3,  HjO,  and  organic  matter  in 
small  variable  quantities. 

Though  the  quantity  of  water  in  the  air  is  marked, — over  1  per 
cent., — it  is  not  customary  to  reckon  it  in  the  gaseous  constituents. 

Some  gases,  as  hydrogen  and  nitrogen,  produce  no  specific  efl:ects 
from  any  toxic  powers  in  themselves  when  they  are  breathed ;  they 
produce  results  simply  because  they  exclude  the  proper  supply  of 
oxygen  for  the  animal.  On  the  other  hand,  gases  such  as  carbon 
dioxide,  carbon  monoxide,  nitrous  oxide,  and  hydrogen  sulphide, 
when  respired  in  sufficient  bulk,  are  absorbed  and  so  produce  specific, 
toxic  effects.  A  third  class  of  gases,  such  as  ammonia  and  nitric 
oxide,  are  not  respirable,  because  of  their  highly  irritant  action  upon 
the  respiratory  apparatus.     Spasm  of  the  glottis  is  produced. 

Carbon  dioxide,  when  undiluted,  is  irrespirable  by  reason  of  the 
spasm  of  the  glottis  produced  by  it.  Properly  diluted  it  can  be 
respired,  but  produces  headache,  dizziness,  drowsiness,  and  dyspnoea 
by  an  action  on  the  nervous  system.  Nitrous  oxide  acts  directly 
upon  the  nervous  system,  partly  by  a  special  action  and  partly  by 
producing  an  excess  of  COg  in  the  blood.  Nitrogen  and  hydrogen 
gases  produce  their  fatal  efi'ects  by  asphyxia,  due  to  exclusion  of  the 
oxygen  and  thereby  preventing  oxygenation  of  the  blood-corpuscles. 
Differing  from  these  gases  are  the  effects  produced  by  inhalation  of 
carbon  monoxide.  It  was  long  known  that  this  gas  was  poisonous, 
but  it  has  only  been  within  recent  years  that  its  mode  of  producing 
asphyxia  has  been  learned.  Instead  of  excluding  the  oxygen,  it 
displaces  the  latter  in  the  blood,  forming  a  very  stable  compound 
with  the  hsemoglobin  of  the  red  corpuscles.  It  is  interesting  to  note 
that  the  color  of  the  blood  after  death  from  asphyxia  from  carbon 
monoxide  is  cherry-red;  in  other  forms  of  asphyxia  the  blood  is 
almost  black.  The  action  of  this  gas  is  of  practical  importance, 
since  every  year  it  is  the  cause  of  many  deaths.  These  occur  from 
poisoning  from  coal-gas  (especially  where  charcoal  stoves  are  used 
in  small  rooms),  the  fumes  of  kilns  and  coke-fires,  and  from  inhaling 
the  air  of  coal-mines,  especially  after  explosions. 

Caissons  and  the  Effect  of  Compressed  Air. — In  caissons  men  are 
able  to  support  during  some  moments  a  pressure  of  five  to  ten  atmos- 
pheres when  they  proceed  with  caution.  If  the  pressure  is  too  rapid, 
there  is  great  danger.     On  decompression  pains  in  the  joints  and 


352  PHYSIOLOGY. 

muscles  ensue,  followed  by  paralysis,  with  deafness  and  vertigo. 
These  symptoms  are  called  "bends." 

When  an  animal  that  resists  a  pressure  of  ten  atmospheres  dies 
instantly  from  a  rapid  change  to  ordinary  pressure,  the  autopsy 
shows  that  the  heart  and  large  vessels  are  filled  with  bubbles  of  gas, 
especially  of  nitrogen.  Under  the  influence  of  double  or  triple  pres- 
sure the  blood  absorbs  a  double  or  triple  proportion  of  air,  especially 
the  nitrogen.  If  the  animal  is  submitted  to  a  rapid  diminution  of 
pressure,  the  nitrogen,  not  being  kept  in  solution  in  the  blood,  is 
disengaged  in  a  gaseous  state  in  the  form  of  bubbles,  which  produce 
embolism  in  the  capillaries  of  the  brain,  lungs,  and  heart,  and  arrest 
the  circulation.  To  avoid  the  disengagement  of  bubbles  of  nitrogen 
it  is  necessary  to  let  the  atmospheric  compression  down  in  a  very 
gradual  manner.  Operatives  on  leaving  the  tubes  in  which  com- 
pressed air  exists  must  remain  a  quarter  to  a  half  hour  in  the  closed 
chambers,  where  the  pressure  is  reduced  little  by  little.  The  excess 
of  gas  absorbed  is  slowly  eliminated  by  the  lungs  without  producing 
an  accident.  Four  atmospheres  is  about  the  amount  that  operatives 
can  work  in  with  safety.  Every  ten  meters  of  depth  in  water  roughly 
equals  one  atmosphere.  By  itself  compressed  oxygen  is  a  toxic 
agent,  for  it  lowers  the  output  of  carbonic  acid  and  the  temperature 
of  the  body.  The  cure  for  caisson-paralysis  is  recompression  and 
slow  decompression. 

Hill  and  McLeod  have  shown  that  in  compressed  air  chambers 
there  was  no  alteration  of  blood-pressure  or  pulse-rate,  or  in  the 
diameter  of  the  blood-vessels,  or  in  the  rate  of  the  flow  of  blood.  A 
rise  of  atmospheric  pressure  exercises  no  mechanical  effect  upon  the 
circulation.  Hill  and  McLeod  have  shown  that  the  oxygen  of  the 
air  compressed  produces  inflammation  of  the  lungs,  just  like  ether 
or  any  other  irritant.  This  inflammation  is  produced  in  an  hour  or 
two  with  high  pressures. 

Bert  has  shown  that  air  under  the  pressure  of  seventeen  atmos- 
pheres, or  pure  oxygen  at  a  pressure  of  three  and  a  half  atmospheres, 
will  produce  in  animals  convulsions  resembling  those  of  strychnia, 
and  death  ensues.  It  is  the  oxygen  itself  that  kills,  due  to  its  being 
compressed. 

Mai  de  Montagne,  Rarefied  Air. — All  travelers  who  have  climbed 
the  Alps  speak  of  the  same  troubles  experienced  by  them  at  nearly 
the  same  altitude:  a  considerable  diminution  of  appetite,  a  disgust 
for  food,  nausea  and  even  vomiting,  palpitations,  headache,  lassitude, 
sleepiness,  and  buzzing  in  the  ears.     This  state  is  known  as  anoxy- 


RESPIRATION.  353 

haemia,  or  want  of  oxygen  in  the  blood.  Dyspnoea  takes  place  not 
only  because  the  air  inspired  contains  oxygen  in  a  given  volume,  but 
also  because  the  dissolution  of  this  gas  in  the  blood  is  less  easy  under 
feeble  pressure.  Muscular  work  in  the  ascent  also  uses  up  consider- 
able of  the  oxygen  taken  in.  At  10  per  cent,  of  an  atmosphere  there 
ensue  restlessness  and  dyspnrea,  and,  at  about  7  per  cent.,  death.  A 
partial  pressure,  like  7  per  cent,  of  an  atmosphere,  corresponds  to 
an  altitude  of  30,000  feet.  Men  in  a  balloon  have  ascended  about 
28,500  feet. 

The  question  arises,  How  do  the  inhabitants  of  high  mountains 
escape  the  effects  of  a  want  of  oxygen  in  the  blood  ?  To  overcome 
this  diminished  absorption  of  oxygen  Nature  adapts  itself  by  increas- 
ing the  number  of  red  corpuscles  in  the  blood.  Then  the  increased 
amount  of  haemoglobin  in  the  blood  can  take  up  more  oxygen,  and 
thus  overcome  the  effects  of  a  rarefied  air. 

In  mountain  sickness  Kronecker  holds  that  there  is  an  increased 
amount  of  blood  in  the  pulmonary  vessels,  due  to  an  increase  in  their 
capacity  and  to  a  stagnation  of  blood  arising  from  an  equalization 
of  the  atmospheric  and  intrathoracic  pressure,  causing  a  passive 
oedema  resulting  in  dyspncea  and  asphyxia. 

Ventilation. — Let  it  suffice  here  to  recall  that  the  problem  of 
ventilation  consists  in  maintaining,  in  more  or  less  closed  spaces,  the 
normal  composition  of  the  atmospheric  air.  Not  only  this,  but  to 
counteract  the  incessant  modifications  the  respiration  of  man  or  of 
animals  makes  this  medium  undergo.  For  these  purposes  it  is 
important  that  the  ventilation  should  be  very  active. 

It  has  been  established  that,  for  closed  spaces  intended  to  receive 
healthy  persons,  it  suffices  that  the  ventilation  furnish  1000  cubic 
feet  of  new  air  per  person  per  hour.  This  is  not  sufficient  for  hos- 
pitals which  contain  sick  persons,  where  more  abundant  and  vitiated 
emanations  are  received  by  patients  less  fitted  to  react  against 
their  influence.  Those  hospitals  which  receive  3000  cubic  feet  of 
fresh  air  for  each  sick  person  hourly  are  free  from  odor. 

A  healthy  adult  gives  off  about  0.6  cubic  feet  of  carbonic  acid 
per  hour.  If  he  be  supplied  with  1000  cubic  feet  of  fresh  air  per 
hour  he  will  add  0.6  to  the  0.4  cubic  feet  of  carbonic  acid  it  already 
contains.    That  is,  he  raises  the  percentage  to  .01. 

Pharmacological.- — The  increase  of  pressure  in  the  pulmonarv 
circulation  and  a  simultaneous  decrease  of  arterial  tension  in  the 
systemic  circulation  by  amyl  nitrite  are  due  either  to  a  contraction 
of  the  pulmonary  vessels  or  to  a  weakness  of  the  left  ventricle,  and 

S3 


354  PHYSIOLOGY. 

as  a  consequence  a  backing  up  of  blood  in  the  left  auricle.  Nitro- 
glycerin acts  like  nitrite  of  amyl.  Aconite  lowers  the  pressure  in 
both  the  pulmonary  and  systemic  circulations,  due  to  a  weakening 
of  both  sides  of  the  heart.  Ergot  constantly  causes  a  marked 
increase  of  pulmonary  tension,  hence  is  not  useful  in  pulmonary 
haemorrhage  with  a  primary  decrease  of  aortic  pressure.  Digitalis, 
strophanthin,  and  adrenal  extract  increase  the  tension  in  the  sys- 
temic circulation,  leaving  the  pressure  in  the  pulmonary  circulation 
unchanged.  It  is  singular  that  the  adrenal  extract  should  so  greatly 
affect  the  systemic  pressure  and  not  the  pulmonary,  whilst  ergot  acts 
reversely — augments  the  pulmonary  pressure  more  than  that  of  the 
aortic  system.  These  facts  show  the  independence  of  the  pulmon- 
ary vessels  to  the  vessels  of  the  systemic  circulation.^ 

The  blood-pressure  in  the  pulmonary  artery  is  about  one-third 
that  in  the  aorta. 

As  to  the  vasomotor  nerves  of  the  lungs,  we  do  not  know  whether 
they  have  a  tonus,  or  under  what  circumstances  they  are  called  into 
activity.  It  is  natural  to  conclude,  since  pulmonary  vasomotor 
nerves  exist,  that  they  are  excited  when  the  left  heart  has  difficulty 
in  emptying  itself ;  in  this  case  they  could  contract  and  diminish  the 
afflux  of  blood  to  the  left  side  of  the  heart. 


^  Tigerstedt,  Ergebnisse  der  Physiologie,  1903. 


CHAPTER  VIII 

SECRETION. 

INTERNAL  SECRETION. 

The  tissue-activity  of  the  organism  may  be  conveniently  classed 
under  three  groups:  (a)  muscular  activity,  manifesting  itself  in  heat 
and  motion;  {h)  nervous  activity,  including  all  nervous  acts,  from 
sensation  to  reason;  (c)  glandular  activity,  which  is  the  general  func- 
tion of  epithelial  and  lymphoid  tissues.  It  includes  all  those  changes 
of  metabolism  whereby  there  follows,  as  a  result  of  elaboration,  a 
special  mixture. 

It  is  with  the  last  of  the  three — glandular  activity — that  we  are 
now  to  deal.  However,  the  human  economy  being  such  a  complex 
organism,  it  must  be  borne  in  mind  that  disturbance  or  lack  of 
activity  of  one  kind  may  have  a  very  marked  influence  upon  other 
metabolic  functions.  It  is  well  known,  especially  among  animal  fan- 
ciers, what  a  great  effect  the  removal  of  the  ovaries  and  testicles 
may  occasion  in  the  development  of  other  organs  and  in  the  general 
nutrition  of  the  body.  Proteid  waste  of  increased  proportion  follows 
the  removal  of  a  considerable  portion  of  renal  tissue.  The  liver  is 
most  intimately  connected  with  the  metabolism  of  carbohydrates  and 
proteids  as  well  as  those  food-constituents  which  contain  iron. 

The  gland-cells  enjoy  an  essential  role  in  secretion.  These  cells 
are  applied  upon  the  basement  membrane  of  the  glandular  acini  in 
such  a  fashion  that  each  cul-de-sac  is  surrounded  by  a  network  of 
capillaries.  Ludwig  and  Tomsa  have  shown  that  between  the  blood- 
capillaries  and  the  acinus  are  found  lymphatic  spaces.  The  cells  of 
the  acinus,  surrounded  by  the  lymph  in  the  spaces,  take  from  it  the 
elements  needed  for  the  production  of  their  own  peculiar  secretion. 

Dependent  upon  the  nature  of  the  activity  of  the  epithelium  of 
the  glands,  the  general  process  of  secretion  may  be  said  to  comprise 
four  distinct  modes: — 

1.  Secretion  by  Filtration. — In  this  case  the  glandular  epithe- 
lium does  not  manufacture  any  material;  it  utilizes  the  principles 
preexisting  in  the  blood  and  lymph.  This  kind  of  secretion  is  related 
to  serous  transudation,  as  of  the  pleurae  and  peritoneum,  but  it  is 
not  a  simple  filtration.  The  selective  action  of  the  epithelium  acts 
upon  the  transit  of  the  secretion  and  varies  the  proportion  of  the 

(355) 


356  PHYSIOLOGY. 

constituents  oi  the  secretion  according  to  the  composition  of  the 
lymphatic  and  blood-plasma.  To  this  style  of  secretion  belong  the 
water  of  the  urine,  the  sweat,  and  the  tears.  The  most  important 
principles  filtered  are  water,  salts  of  the  plasma,  chlorides  of  potas- 
sium, sodium  phosphates,  lime,  magnesia,  and  carbonic  acid. 

2.  Secretion  Proper  —  Production  of  New  Principles.  —  Here 
glandular  activity  cs])ecially  intervenes;  the  epithelial  cell  does  not 
act  as  a  simple  filter.  It  modifies  the  nature  of  those  products  pass- 
ing through  it,  or  creates  from  them  new  products.  In  this  class 
may  be  put  the  digestive  secretion.  The  products  thus  formed  by 
gland-cells  vary  for  each  gland;  neither  physiology  nor  histology  is 
able  to  explain  their  manner  of  production.  Thus,  we  are  not  able 
to  exjilain  in  a  satisfactory  manner  the  chemical  changes  which  make 
hydrochloric  acid  appear  in  the  gastric  juice,  sulphocyanide  of  potas- 
sium in  the  saliva,  l)ik'  acids  in  the  bile,  etc. 

3.  Secretion  by  Glandular  Desquamation. — In  the  preceding 
types  of  secretion  the  gland-cell  preserves  its  integrity;  it  does  not 
do  anything  else  except  to  allow  the  external  materials  to  pass 
through  it,  changed  or  unchanged.  However,  in  this  type  the  cell 
itself  falls  and  is  eliminated  to  contribute  to  the  formation  of  the 
product  of  secretion.  This  glandular  desquamation  is  comparable  to 
the  epithelial  desquamation  which  occurs  during  the  life-history  of 
the  epidermis.  Generally  this  desquamation  is  preceded  by  a  chem- 
ical change  of  the  gland-cells.  This  change  is  fatty,  as  in  sebaceous 
secretion.  The  sebaceous  fats  and  mucin  form  the  special  products 
of  this  group  of  secretions. 

4.  Morphological  Secretion. — In  this  type  the  essential  element 
of  the  secretion  is  a  formed  element.  It  is  a  specialized  cell  derived 
from  a  cell,  together  with  a  liquid  which  holds  this  anatomical  ele- 
ment in  suspension.     Such  is  the  spermatic  fluid. 

Secretion  Defined. — The  term  secretion  has  been  defined  as  the 
result  of  the  special  activity  of  the  glandular  tissues.  It  is  the  elab- 
oration of  fluid  or  semifluid  mixtures  by  selection  and  formation 
from  the  fluids  which  surround  the  active  cells,  as  well  as  from  the 
substances  of  the  cells  themselves.  Up  to  a  certain  point  secretion 
is  composed  of  two  acts  which  are  separated  by  a  distinct  line  of 
demarcation. 

1.  Lymph  passes  through  the  wall  of  the  capillary.  This 
lymph  spreads  into  the  lymph-spaces  which  surround  the  acini,  and 
it  is  from  this  lymph  that  the  elements  are  taken  out  for  the  pro- 
duction  of    the   secretory   products.     The   filtration   is   under  the 


SECRETION.  357 

mfluence  of  the  blood-pressure,  and  varies  in  its  intensity  as  the 
arterial  tension  varies.  It,  properly  speaking,  is  an  accessory  act  of 
secretion. 

2.  The  second  feature  is  the  activity  of  the  gland-cells,  which 
take  from  the  lymph  the  materials  necessary  for  secretion,  to  change 
them  more  or  less.  This  phase  is  the  essential  act  of  secretion.  It 
is  dependent  upon  filtration  to  the  extent  that  filtration  furnishes 
the  liquid  which  the  glandular  cells  need  and  renews  it  when 
exhausted. 

The  activity  of  the  gland-cells  attains  its  maximum  in  general 
during  the  apparent  repose  of  the  gland.  When  the  gland  is  not 
secreting,  its  cells  are  preparing  substances  peculiar  to  each  secre- 
tion. This  is  true  particularly  of  the  ferments,  as  pepsinogen, 
trypsinogen,  etc. 

The  two  processes — filtration  and  gland-cell  activity — may  be 
separated  from  one  another  without  producing  any  interference. 
Thus,  secretion  can  continue  when  the  head  is  amputated,  and  even 
if  the  circulation  of  the  gland  be  arrested.  Salivation  can  continue 
after  both  these  events  have  occurred. 

On  the  other  hand,  the  injection  of  carbonate  of  soda  into  the 
salivary  duet  destroys  the  gland  activity  without  affecting  the  cir- 
culation of  the  gland.  Should  the  chorda  tympani  be  stimulated 
filtration  from  the  blood  continues,  but  the  gland  does  not  secrete. 
There  is  an  accumulation  of  lymph  in  the  lymph-spaces  until  the 
gland  becomes  CBdematous. 

NATURE  OF   INTERNAL  SECRETION. 

This  is  not  the  same  for  all  of  the  glands.  The  secreted  pro- 
duct may  be  destined  to  destroy  the  noxious  principles  resulting 
from  the  functions  of  the  organ,  as  of  the  liver  and  suprarenal  cap- 
sules. Its  aim  may  be  to  break  up  the  excess  of  sugar,  as  is  the 
case  with  the  pancreas;  or  to  prevent  excess  of  a  colloid  material, 
as  with  the  thyroid  gland.  The  enrichment  of  the  blood  with  use- 
ful principles  is  accomplished  by  the  sugar  of  the  liver.  The  testicle 
ex'tract  supplies  more  nervous  energy. 

THE  THYROID. 

The  thyroid  gland,  when  fully  developed,  has  no  excretory  duct; 
so,  with  the  spleen,  suprarenal  bodies,  and  thymus,  it  is  usually 
classed  under  the  head  of  ductless  glands. 

The  thyroid  is  a  soft,  reddish  body  embracing  the  front  and 


358 


PHYSIOLOGY. 


sides  of  the  upper  extremity  of  the  trachea.  It  consists  of  a  pair 
of  lateral  lobes  united  at  their  lower  part  by  a  transverse  isthmus. 
The  lateral  lobes  are  oblong,  oval,  thicker  below  than  above,  and 
usually  of  unequal  length.  The  weight  of  the  thyroid  is  usually 
from  one  to  two  ounces,  but  is  larger  in  the  female.  It  is  very  liable 
to  become  hypertrophied,  especially  in  the  female;  then  it  is  called 
goiter. 

The  thyroid  is  a  highly  vascular  organ,  invested  with  a  thin, 
fibrous  membrane,  and  composed  of  a  fibrous  stroma,  in  the  meshes 
of  which  a  multitude  of  minute  closed  vesicles  exist. 


Fig.  144. — Structure  of  the  Thyroid  (Morat  and  Doyon).  Lobule  of 
the  Thyroid  after  an  Injection  of  the  Lymphatic  Vessels  with  Nitrate 
of  Silver.     Semi-schematic.      (Vialleton.  ) 

1,  1,  Vesicles.  2,  Their  colloid  contents.  3,  3,  Lymphatic  vessels  with  epithe- 
lium stained  with  silver.  4,  Blood  capillary.  5,  5,  Cells  in  the  walls  of  the 
vesicles. 


Each  little  lobule  seems  to  be  a  completely  closed  sac — at  least, 
no  tubule  is  noticed  emanating  from  it.  The  little  sacs  are  filled 
with  a  transparent,  amber-colored,  viscid,  nucleo-albuminous  fluid. 
In  the  connective  tissue  surrounding  each  lobule  there  is  a  plexus 
of  capillaries.  With  them  there  is  found  an  abundant  supply  of 
lymphatics. 

Vessels  and  Nerves. — The  arterial  supply  for  the  thyroid  body 
is  gained  from  the  superior  and  inferior  thyroid  arteries.  These 
arteries  are  remarkable  for  their  large  size  and  numerous  anasto- 
moses. The  veins  form  a  plexus  upon  the  front  of  the  trachea  and 
surface  of  the  gland.     From  the  plexus  arise  the  superior,  middle, 


SECRETION. 


359 


and  inferior  veins.  The  lymplmtics  terminate  in  the  thoracic  and 
right  lymphatic  ducts.  The  nerve-supply  to  the  thyroid  body  is 
derived  from  the  middle  and  inferior  cervical  ganglia  of  the  sympa- 
thetic and  the  pneumogastric.  Their  nonmedullated  fibers  adhere 
very  closely  to  the  vessels. 

Function. — It  was  shown  by  one  observer  that  gentle  pressure 
upon  the  lobes  of  the  gland  caused  the  contents  of  the  gland-acini, 
or  vesicles,  to  flow  into  the  peripheral  lymphatics.     This  was  later 


Fig.  145. — Parathyroid  of  Dog  (Morat  and  Doyon).      (Vialleton.) 

c,  Capsule,  c.c.  Partition  of  connective  tissue  in  the  thickness  of  the  organ. 
c.p.    Epithelial    cell   of  the    parathyroid,      v.    Capillary. 


confirmed  by  the  work  of  microscopists,  and  the  colloid  nature  of  the 
secretion  was  also  recognized.  The  vesicular  epithelium  is  a  true 
secretory  gland-tissue  which  separates  the  colloid  material  from  the 
blood.  The  secretory  character  of  the  epithelium  has  been  further 
shown  by  the  injection  of  pilocarpine.  Following  its  administration 
there  results  a  remarkable  increase  in  secretion  of  the  colloid  sub- 
stance. It  has  been  demonstrated  that  the  expressed  juice  of  a  thy- 
roid gland  of  a  dog  produced  coma  in  another  animal  three  hours 
after  its  administration. 


360 


PHYSIOLOGY. 


Hence  it  must  be  concluded  that  the  thyroid  gland  is  a  struc- 
ture essentially  connected  with  the  metabolism  of  the  blood  and 
tissues.  In  performing  its  functions  it  is  a  blood-agent,  both  directly 
and  indirectly.  In  the  human  foetus  the  gland-tubes,  or  rather 
cylinders  of  epithelium,  commence  their  secretory  activity  during 
the  interval  from  the  sixth  to  the  eighth  month.  In  proportion  to 
the  body-weight,  the  gland  is  heaviest  at  birth  and  diminishes  not- 
ably toward  the  end  of  life.     Therefore  the  thyroid  gland  is  in  f unc- 


Fig.   146. — Illustrating  Nicholson's  Article  on  Thyroid  Treatment  in  a 
Cretin   (Arch,  of  Ped.,  June,  1900).      (Raymond.) 

A,  Before  treatment.    B,  After  treatment. 

tional  activity  before  birth,  and  is  of  special  metabolic  importance 
in  early  extra-uterine  life.  Its  value  falls  as  the  general  vital  pro- 
cesses decrease. 

The  thyroid  body  is  one  of  those  organs  of  great  metabolic 
importance,  since  its  removal  or  disease  is  followed  by  general  dis- 
turbances.    Experimental  thyroidectomy  is  very  much  more  fatal  in 


SECRETION.  361 

young  animals  than  in  adults.  The  removal  of  the  gland  in  aged 
carnivora  is  followed  by  the  usual  cachexia. 

Cachexia  Strumipkiva  has  been  found  by  all  observers  to 
occur  with  greater  frequency  when  thyroidectomy  has  been  per- 
formed on  young  individuals. 

The  classification  of  symptoms  from  removal  of  the  thyroid  is 
either  (a)  tetany,  (6)  myxcedema,  or  (c)  cretinism.  According  to 
the  violence  of  the  cachexia,  death  may  occur  in  any  of  these  stages. 

The  nervous  symptoms  appear  early  and  are  well  marked.  The 
first  indication  is  fibrillary  muscular  tremor  or  twitching,  resembling 
very  closely  the  disease  called  tetany;  next  tremor  occurs;  and 
finally  rigidity  makes  its  appearance.  Some  experimentalists,  as  Gley, 
hold  that  it  is  the  removal  of  parathyroids  which  causes  tetany,  and  not 
the  removal  of  the  thyroid.     The  tetany  seems  to  be  spinal  in  origin. 

When  the  thyroid  body  is  diseased  or  removed  fro7n  children  so 
that  its  functions  are  obliterated,  there  is  produced  a  species  of 
idiocy  called  cretinism. 

A  like  condition  in  adults  receives  the  name  of  myxcedema. 
IS'oticeable  symptoms  of  this  disease  are  slowness  of  both  body  and 
mind,  associated  with  tremors  and  twitchings.  There  is  also  a 
peculiar  condition  of  the  skin  wherein  there  is  overgrowth  of  the 
subcutaneous  tissue.  In  time  this  becomes  replaced  by  fat.  Myx- 
cedema was  believed  to  be  an  oedematous  condition  characterized  by 
the  presence  of  a  large  amount  of  mucin.  That  there  is  an  excess 
of  mucin  has  been  determined,  but  it  is  not  in  proportion  to  produce 
this  pathological  condition.  The  disease  is  rather  a  hyperplasia  of 
the  connective  tissue.  The  integument  especially  swells  and  the  eye- 
lids become  pufPy.  At  the  same  time  the  surface  becomes  dry  and 
there  is  a  tendency  to  shed  hairs  and  superficial  epithelium.  The 
hyperplastic  change  is  followed  by  atrophic  changes,  accompanied  at 
first  by  slight  fever;   later  the  temperature  becomes  subnormal. 

All  of  these  various  effects  of  thyroidectomy  can  be  temporarily 
prevented  by  a  graft  of  thyroid;  they  may  also  be  caused  to  disap- 
pear either  by  injection  of  thyroid  juice  into  a  vein  or  under  the 
skin.  The  same  results  may  be  attained  by  raw  thyroid  or  thyroid 
juice  by  the  mouth.  If  a  graft  can  be  made  to  "take,"  the  effects 
are  permanent.  Eemoval  of  a  permanent  graft  will  be  followed  by 
all  the  symptoms  of  thyroidectomy. 

The  phenomena  attending  extirpation  are  due  to  the  absence 
of  a  secretion  which  is  fonned  within  the  thyroid,  passing  from  it 
into  the  blood.     This  secretion  is  necessary  for  certain  of  the  meta- 


362  PHYSIOLOGY. 

bolic  processes  of  the  animal  economy,  especially  for  those  connected 
with  the  nutrition  of  the  central  nervous  system  and  connective 
tissues.  Extracts  of  thyroid  gland  produce  distinct  pathological 
effects  in  the  normal  subject.  An  injection  into  a  vein  of  the  decoc- 
tion of  the  gland  lowers  the  blood-pressure  and  increases  the  caliber 
of  the  radial  artery.  From  this  it  would  seem  that  the  juice  has  a 
distinct  action  upon  the  vascular  system. 

Whether  the  gland  possesses  the  function  of  destroying  toxic 
products  of  metabolism  which  would  otherwise  tend  to  accumulate 
in  the  blood  is  a  point  not  as  yet  understood. 

Because  of  the  extreme  vascularity  of  this  organ  and  its  direct 
connection  with  the  vessels  which  supply  blood  to  the  head,  the  thy- 
roid has  been  regarded  as  exercising  a  regulatory  function  on  the 
blood-supply  to  the  brain — short-circuiting  the  cerebral  flow,  as  it 
were. 

Experiments  have  shown  that  at  least  a  part  of  the  thyroid 
gland  must  be  allowed  to  remain  after  operations  upon  this  gland. 
Otherwise,  cachexia  will  follow. 

The  occurrence  of  thyroid  tissue  in  other  parts  than  the  lobes 
of  the  glands  is  a  matter  of  more  than  embryological  interest. 
These  glandular  masses  have  been  termed  accessory  thyroid  glands, 
or  parathyroids.  The  parathyroids  lie  in  the  immediate  neighbor- 
hood of  the  lobes  of  the  thyroid  gland.  It  has  been  observed,  after 
complete  thyroidectomy  in  man,  that  these  islands,  or  parathyroids, 
become  enlarged.  Also,  where  temporary  symptoms  of  cachexia  have 
appeared,  they  improve  in  proportion  to  the  degree  of  swelling  of 
the  parathyroids. 

The  thyroid  contains  two  albuminous  bodies,  the  one  containing 
iodine,  the  other  having  phosphorus.  The  first  one  has  the  char- 
acter of  a  globulin  and  has  received  the  name  of  thyreoglobulin  and 
by  reagents  is  changed  into  iodothyrin. 

Hutchinson  states  that  "if  the  presence  of  iodine  in  iodothyrin 
is  essential  to  the  activity  of  this  substance,  it  is  not  so  in  virtue  of 
its  being  iodine,  but  owing  to  the  form  of  organic  combination  in 
which  it  occurs."  It  is  estimated  that  the  normal  thyroid  gland 
contains  approximately  ten  times  as  much  iodine  as  do  the  hyper- 
trophied  glands  of  patients  suffering  from  exophthalmic  goiter. 
The  thyroid  seems  to  possess  a  peculiar  affinity  for  iodine. 

While  our  knowledge  of  the  thyroid  has  been  considerably 
extended  by  reason  of  modern  research,  there  yet  remains  much 
that  is  very  obscure.     Thus,  the  accessory  thyroid  glands,  or  para- 


SECRETION.  363 

thyroids,  are  free  masses  of  tissue  located  in  the  vicinity  of  the  thy- 
roid which  seem  to  contain  no  colloid  material.  Xevertheless,  their 
removal,  although  the  bulk  be  small,  produces  identical  results  with 
the  complete  removal  of  the  thyroid  gland.  Eegarding  the  function 
of  the  jjarathyroids,  it  is  probable  that  they  are  concerned  in  remov- 
ing something  from  the  blood  rather  than  adding  anything  to  it. 

Thyroid  by  the  mouth  reduces  weight  by  an  increase  of  the 
intake  of  oxygen  and  the  output  of  carbon  dioxide.  This  excessive 
burning  of  fat  produces  water,  thus  causing  increased  secretion  of 
urine.  It  also  increases  the  urinary  nitrogen,  probably  due  to  pro- 
teid  changes.     It  acts  best  in  the  pale,  fat  person. 

Von  Cyon  has  made  a  full  study  of  the  relation  of  the  thyroid 
to  the  heart.     He  states  that  suppression  of  the  activity  of  the  thy- 


X 

IcSoihurlrx  Rabbits 

Fig.  147. — Effect  of  lodothyrin  on  Intestinal  Peristalsis. 
It  increases   the  extent  of  the   peristaltic  movements. 

roid  or  an  injection  of  iodothyrin  has  an  immense  influence  upon 
the  entire  nervous  system  of  the  heart  and  blood-vessels.  He  proves 
that  the  vagus  participates  in  the  innervation  of  the  thyroid  gland, 
or  is  at  least  closely  connected  with  it.  The  function  of  the  thyroid 
is  to  render  harmless  the  salts  of  iodine,  which  have  a  toxic  effect 
upon  the  vagi  and  sympathetic  nerves  by  converting  them  into  an 
organic  compound,  the  iodothyrin.  The  latter  compound  has  a 
stimulating  effect  upon  these  same  nerves  and  at  the  same  time 
increases  their  power.  The  thyroid  acts  mechanically  as  a  safeguard 
of  the  brain  against  engorgement.  In  a  sudden  increase  of  blood- 
pressure,  whether  from  increased  activity  of  the  heart  or  from 
increased  capillary  resistance,  the  thyroid  is  capable  of  passing 
through  its  vessels  a  large  amount  of  blood  within  a  very  short  time, 


364  PHYSIOLOGY. 

so  as  to  take  it  back  directly  from  the  arterial  into  the  venous  sys- 
tem and  thus  i^revent  its  entrance  into  the  cerebral  circulation. 

THE  SPLEEN. 

The  spleen  is  deeply  placed  in  the  left  hypochondrium.  Its 
shape  is  a  half-ovoid.  Its  consistency  is  comparatively  soft,  and  its 
color  is  purplish.  Its  external  convex  surface  is  in  contact  with  the 
diaphragm  opposite  the  three  or  four  lower  ribs.  Its  internal  sur- 
face is  applied  to  the  fundus  of  the  stomach,  to  which  it  adheres  by 
the  gastro-splenic  omentum.  In  the  middle  of  the  internal  surface 
of  the  spleen  there  is  a  slight  groove,  the  hilus,  where  the  artery  and 
nerves  enter.  The  spleen  usually  is  five  inches  in  length,  four  inches 
in  breadth,  and  from  one  to  one  and  one-half  inches  thick.  It  has 
two  coats:    the  outer  serous  and  the  inner  fibro-elastic. 

The  spleen  when  torn  has  a  deep  reddish-black,  pulpy  appear- 
ance, resembling  coagulated  blood.  This  splenic  pulp  may  be 
removed  from  the  spleen  by  maceration,  leaving  a  spongy  mass  com- 
posed of  splenic  blood-vesse's  associated  with  numerous  trabeculag 
of  fibro-elastic  tissue.  Adhering  to  the  side  of  the  smallest  arteries 
of  the  spleen  are  small,  rounded,  whitish  bodies,  the  corpuscles  of 
Malpighi,  one-thirtieth  to  one-sixtieth  of  an  inch  in  diameter.  The 
splenic  pulp  contains  red  blood-corpuscles,  granular  corpuscles  re- 
sembling lymphocytes  in  appearance,  having  an  amoeboid  movement, 
and  red  corpuscles  undergoing  disintegration. 

Function. — The  extirpation  of  the  spleen  leaves  life  and  health 
intact  in  animals  and  in  man.  All  that  results  is  a  more  or  less  pro- 
nounced hypertrophy  in  all  the  lymphatic  ganglia  of  the  body. 

Direct  irritation  of  the  spleen,  the  direct  or  reflex  irritation  of 
the  medulla  oblongata,  the  application  of  ice-water  to  the  left  hypo- 
gastrium,  and  quinine  canise  a  diminution  of  the  spleen  by  contrac- 
tion of  the  muscles  of  the  capsule  and  trabecula.  The  spleen  is  con- 
gested during  digestion,  and  when  the  portal  circulation  is  interfered 
with,  and  in  a  great  number  of  infectious  diseases,  notably  typhoid 
and  malarial  fevers.  The  spleen  is  supposed  by  some  to  manufac- 
ture white  blood-corpuscles,  and  this  manufacturing  reaches  a  pro- 
nounced activity  when  the  organ  is  hypertrophied,  as  in  leuco- 
cythasmia.  The  spleen,  from  its  power  to  dilate,  serves  as  a  reser- 
voir of  blood  for  the  portal  system,  especially  for  the  blood-vessels 
of  the  stomach.  Many  of  the  purin  bodies  are  found  in  the  spleen, 
as  xanthin,  hypoxanthin,  and  uric  acid. 


SECRETION. 


365 


Influence  of  the  Nervous  System  Upon  the  Spleen. — The  nerves 
that  supply  the  spleen  have  their  center  in  the  medulla  oblongata. 
Section  of  these  nerves  is  followed  by  an  increase  in  the  size  of  the 
organ. 

It  has  been  shown  by  the  oncometer  that  the  spleen  undergoes 
rhythmical  contractions  and  dilatations  by  virtue  of  the  regular  con- 


Fig.   148. — Effect  of  Extract  of  Spleen  on  Intestinal  Peristalsis. 

traction  and  relaxation  of  the  muscular  fibers  found  in  its  capsule 
and  trabecular.  Jones,  of  Baltimore,  has  shown  that  the  spleen  con- 
tains adenase,  a  ferment  which  converts  adenin  into  hypoxanthin. 

I  have  demonstrated  experimentally  that  extract  made  from  the 
spleen  when  injected  into  an  animal  will  excite  active  peristaltic 
movements. 

C.s.d   ^ 


Fig.  149. — Adrenal  Capsules  of  a  Rabbit.      (Morat  and  Doyon.) 
C.s.d,   C.s.g,   Capsules.    B.d,  R.g,   Kidneys.     V.g,  Ureters.     A,  Aorta. 
T.c,  Vena  cava. 

THE  ADRENALS. 

The  adrenals  are  a  pair  of  flattened  triangular  organs,  one  being 
situated  upon  the  upper  end  of  each  kidney  and  inclined  inwardly 
toward  the  vertebral  column.  Their  posterior  surface,  moderately 
convex,  rests  against  the  crura  of  the  diaphragm ;  their  anterior  sur- 
face, flatter  than  the  posterior,  on  the  right  side  is  in  contact  with 
the  liver,  on  the  left  side  with  the  pancreas  and  spleen.     The  sur- 


366 


PHYSIOLOGY. 


faces  present  vascular  furrows,  the  largest  of  which  at  the  base  is 
distinguished  as  the  hilus.  These  adrenals  are  brownish-yellow  in 
color,  of  moderately  firm  consistence,  and  vary  in  size  in  different 
individuals  and  slightly  on  the  two  sides.  Usually  they  are  about 
one  and  one-half  inches  in  breadth  and  height,  and  about  one-fourth 
of  an  inch  in  thickness.     On  section  we  find  an  external  layer,  the 

cortex,  and  an  internal  layer  of  softer 
substance,  the  medulla. 

The  cortical  layer  is  yellow  in 
color,  of  firm  consistence,  and  pre- 
sents a  columnar  appearance  at  right 
angles  to  the  surfaces  of  the  layer. 
Microscopically,  it  contains  oblong  re- 
ceptacles, occupying  a  fibrous  stroma 
continuous  with  the  fibrous  coat  of  the 
body.  In  these  receptacles  are  nu- 
cleated, transparent  cells  often  con- 
taining oil-globules  and  a  yellowish- 
brown  pigment.  Beneath  the  cap- 
sule is  the  zona  glomerulosa,  with  cells 
in  round  groups;  the  next  is  zona 
fasciculata,  with  cells  in  columns; 
and  the  last  is  zona  reticularis. 

The  medullary  substance  is  com- 
posed of  very  irregularly  shaped  cells, 
rather  closely,  but  irregularly,  packed 
into  a  meshwork  of  fibrous  tissue.  In 
the  interstices  lie  masses  of  multinu- 
cleated protoplasm,  blood-vessels,  and 
an  abundance  of  nerve-fibers  and  cells. 
The  cells  of  the  medulla  are  conspicuous  in  that  they  contain 
certain  reducing  agents.  The  agent  which  gives  color-reactions  has 
been  termed  chromogen.  Just  what  this  agent  is  chemically  is  not 
known,  but  it  is  believed  to  be  the  principle  which  raises  blood-pres- 
sure when  suprarenal  extracts  are  injected  subcutaneously.  The 
active  principle  is,  according  to  Abel,  epinephrin;  according  to 
Takamine,  adrenalin.  Adrenalin  has  been  prepared  synthetically  by 
Professor  Hans  Meyer,  of  Marburg,  from  methylaminoorthodioxy- 
acetphenon.  It  constricts  arterioles,  contracts  the  iris,  and  produces 
glycosuria,  like  adrenalin.^ 

^  The  cortex  of  the  adrenal  secretes  choline. 


P'ig.    150. — Section  of   Adrenal. 

(VlALLETON.) 

1,  Fibrous  capsule.  2,  Zona 
glomerulosa.  3,  Zona  fasciculata. 
4,  Zona  reticularis.  5,  Medulla. 
6,   Blood-vessel.     7,  Central  vein. 


SECRETION. 


367 


Adrenalin  is  a  white,  crystalline  substance  with  bitter  taste, 
slightly  soluble  in  water,  and  stable  in  dry  state.  It  absorbs  oxygen 
from  the  air,  and  is  a  strong  reducing  agent  in  alkaline  and  neutral 
solution.  Its  solution  becomes  red  on  standing.  Chemically,  it 
appears  to  be  a  secondary  alcohol,  and  it  is  CgHg  (OHo).  CH  (OH) 
CH2.  NH.  CH3.  In  the  adrenals  of  patients  dead  of  Addison's  dis- 
ease there  was  no  adrenalin. 

Blood-supply. — The  blood-vessels  of  these  suprarenal  bodies  are 
numerous.  Each  is  supplied  by  the  suprarenal  artery  from  the  aorta, 
together  with  branches  from  the  contiguous  phrenic  and  renal  arte- 
ries. When  the  arteries  enter  the  organ  they  ramify  through  the 
fibrous  stroma  and  terminate  in  capillaries  surrounding  the  recep- 


mu^/\/wv\/\i\Aj\/v\M'\/\iW^^ 


Fig.   151. — Effect  of  Adrenalin  on  the  Volume  of  Inspired  and  Expired 

Air.     Tracing  with  Gad's  Aeroplethysmogi-aph. 

First    line,    normal.      Second    and    third    lines,    showing    the    diminution    of 
volume   of   air    inspired. 

tacles  of  the  granular  cell-contents.  The  nerves  are  chiefly  derived 
from  the  solar  and  renal  plexuses  of  the  sympathetic  system,  and  are 
very  numerous  for  the  size  of  the  organ. 

Function. — The  function  of  the  suprarenal  bodies  is  still  very 
obscure.  The  discovery  that  a  relation  existed  between  the  bronzing 
of  the  skin  of  Addison's  disease  and  a  diseased  condition  of  the  supra- 
renals  was  a  signal-point.  It  was  learned  that  these  small  bodies  are 
indispensable  to  life.  The  phenomena  ensuing  from  their  extirpa- 
tion are  due  to  a  chemical  alteration  of  the  blood,  and  not  to  trauma. 
The  ablation  of  one  capsule  is  not  necessarily  mortal,  but  the  destruc- 
tion of  both  produces  death  very  quickly.  In  the  rabbit  death  follows 
in  nine  hours ;  in  the  guinea-pig,  in  three  hours.  Death  is  preceded 
by  a  considerable  weakness,  true  paralysis  of  the  members  and  respira- 
tory muscles,  and  epileptiform  convulsions. 


368 


PHYSIOLOGY. 


If  the  blood  of  animals  dying  from  removal  of  the  capsules  be 
transfused  into  an  animal  that  has  just  undergone  the  operation, 
there  is  produced  a  very  rapid  paralysis  and  death.  Injecting  an 
extract  of  the  capsules  into  an  animal  from  which  the  capsules  have 
been  removed  slowed  the  symptoms  and  prolonged  life.  Hence,  it 
has  been  concluded  that  the  chief  function  of  the  suprarenal  capsules 


Fig.   152. — Effect  of  Adrenalin  on  Intestinal  Peristalsis. 

is  the  neutralization  of  a  poison  analogous  to  curare.  The  means  by 
which  this  is  accomplished  is  a  poison-destroying  secretion  in  their 
cells.  The  poison  to  be  neutralized  is  manufactured  in  the  organism 
and  accumulates  in  the  blood  in  instances  of  lesion  or  removal  of  the 
suprarenals. 

The  effects  of  adrenalin  upon   any  tissue   are   such  as   follow 
excitation  of  the  sympathetic  nerve,  which  supplies  the  tissue.     It 


Fig.  153. — Cat.     One  drop  of  adrenalin  solution  and  ten  drops  of  1-per- 
cent, solution  of  nitroglycerin,  mixed  and  then  injected  per  jugular. 

The    adrenalin    counteracted    the    pressure-lowering    by    the    nitroglycerin. 

stimulates  the  myoneural  substance  or  receptive  substances  of  cells. 
It  can  be  used  as  a  test  for  the  existence  of  sympathetic  nerves 
in  any  organ.  Its  effects  on  one  organ  are  shown  by  contraction ; 
in  another  organ  by  inhibition.  Thus,  it  causes  contraction  of  the 
spleen  and  inhibition  of  the  movements  of  the  stomach,  but  in  each 
case  it  resembles  the  effect  of  stimulation  of  the  sympathetic  nerve 


SECRETION. 


369 


going  to  those  organs.  It  is  contraindicated  in  pulmonar}^  haemor- 
rhage. In  default  of  sympathetic  innervation,  plain  muscle  is  indif- 
ferent to  adrenalin.  Ott  first  showed  that  adrenal  extract  arrests 
peristalsis  in  diastole.  This  has  been  confirmed  by  several  observers. 
Blum  has  shown  that  adrenalin  causes  glycosuria  by  action  on  the 
glycogen  of  the  liver, 

Oliver  and  Schafer  found  that  when  extracts  of  the  suprarenals 
were  injected  into  the  circulation  very  noticeable  phenomena  resulted. 


hmhiihhmhMhmhJMtJMMhhMIMh^^ 


tjf^ixMMMiOmnntmjmtuoiwuviMM^^ 


lWi^ 


ViAWiMA/ihAMA«m/l/lWlWiAMnAWih,iWiW^ 


Fig.  154. — Turtle's  Heart,  Suspended  by  Lever. 

1,  Normal  curve.     2,  3,  4,   Curves  after  the  gradual  application  to   the  heart 
of   seven   drops   of  adrenalin  solution. 

Thus  the  arteries  become  greatly  contracted,  and  the  blood-pressure 
rises  very  rapidly.  This  vasoconstrictor  action  is  independent  of  the 
main  vasomotor  center,  which   I  have  confirmed. 

Adrenalin  is  a  great  muscle  tonic,  for  it  makes  the  cardiac  con- 
traction higher.  It  also  slows  the  heart  by  a  stimulation  of  the  cen- 
tral end  of  the  vagus.  It  stimulates  the  unstriped  muscle  of  the 
arterioles  through  the  myoneural  substance,  hence  is  a  great  vasocon- 
strictor, and  thus  arrests  haemorrhage.  On  striated  muscle  it  pro- 
longs contracture  and  thus  causes  the  muscle  to  be  slower  in  relaxing. 

24 


370 


PHYSIOLOGY. 


Nearly  all  the  adrenalin  is  destroyed  in  the  hody,  but  1  have 
shown  that  a  minute  quantity  is  excreted  by  the  kidneys.  One  one- 
millionth  of  a  gram  of  the  dried  gland  will  elevate  the  arterial 
tension. 

The  splanchnics  are  supposed  to  contain  the  secretory  nerves  of 
the  adrenals. 

In  rabbits  during  pregnancy  the  suprarenal  bodies  enlarge,  the 
outer  cortex  being  twice  the  size  of  the  medulla  and  inner  cortex. 
Sexually  precocious  children  have  hypertrophied  suprarenal  capsules. 
Atrophy  of  suprarenal  capsules  is  associated  with  want  of  pubic  hair 
and  of  development  of  the  genital  organs.  Hence  the  cortex  of  the 
adrenal  is  probably  connected  with  the  growth  of  the  body  and  the 
development  of  puberty  and  sexual  life. 


Fig.  155. — Efl'ect  of  Suprarenal  p]xtract  upon  Muscle-contraction  in  the 

Frog.       { SCHAFEB. ) 

A,  Normal  muscle  curve  of  gastrocnemius.  B,  Curve  taken  during  supra- 
renal poisoning,  but  otherwise  under  the  same  conditions  as  A;  time  trac- 
ing;    100  per  second. 

THE  THYMUS. 

The  thymus  body  is  a  temporary  organ  which  increases  in  size 
from  the  embryo  up  to  two  years  after  birth,  and  sul)sequently 
dwindles  away.  It  occupies  the  upper  part  of  the  anterior  medias- 
tinal cavity  behind  the  sternum  and  extends  into  the  neck  frequently 
to  the  thyroid  gland.  It  rests  upon  the  pericardium,  aorta,  and  the 
trachea.  It  is  a  flat,  triangular  body,  consisting  of  a  pair  of  lateral  and 
unequal  lobes.  It  is  of  a  pinkish-cream  color,  and  varies  in  size  and 
weight  not  only  according  to  age,  but  also  in  different  persons.  At 
birth  it  is  about  two  inches  long  and  one  and  one-half  inches  wide  at 
the  lower  part  and  two  or  three  lines  thick.     It  is  composed  of  numer- 


SECRETION.  371 

ous  angular  lobules  mixed  with  connective  tissue.  The  lobules  are  sub- 
divided into  follicles,  and  each  follicle  has  a  cortex  and  medulla.  In 
the  medulla  are  spherelike  bodies  known  as  the  concentric  corpuscles 
of  Hassall. 

Chemical  Composition. — The  thymus  is  principally  a  lymph- 
gland.  Nothing  special  is  known  of  the  concentric  corpuscles.  The 
presence  of  extractives,  like  xanthin,  hypoxanthin,  leucin,  and  adenin 
has  been  noted.  The  alkaline  reaction  of  life  becomes  rapidly  acid 
after  death.     The  acid  is  sarcolactic  acid. 

The  main  constituent  of  the  cells  is  proteid,  especially  nucleo- 
proteid.  The  total  percentage  in  the  thymus  gland  is  about  13.29 
per  cent.  When  it  is  desired  to  produce  experimental  intravascular 
clotting,  the  thymus  is  usually  employed  as  the  source  for  the  nucleo- 
proteid.  This  property  is  not  characteristic  of  the  thymus,  for  it  is 
found  in  all  protoplasm. 

Function. — Extirpation  gives  few  positive  results,  but  chemical 
investigation  shows  that  the  parenchyma  of  the  gland  contains  a  large 
number  of  products  that  indicate  that  it  possesses  very  considerable 
metabolic  activity.  As  long  as  the  thymus  gland  exists,  it  seems  to 
take  part  in  the  production  of  white  corpuscles  like  other  varieties  of 
lymphatic  tissue.  Some  authors  claim  for  it  the  production  of  red 
corpuscles  in  early  life. 

Extracts  of  the  thymus,  when  injected  subcutaneously,  have  been 
shown  by  Ott  to  increase  the  pulse-rate,  with  a  momentary  rise 
of  pressure,  followed  by  a  fall.  This  has  been  confirmed  by  Svehla 
and  Swale  Vincent.  Svehla  found  that  extirpation  of  the  thymus 
of  the  frog  kills  it.  Swale  Vincent,  however,  did  not  find  that  re- 
moval of  the  gland  of  the  frog  was  necessarily  fatal,  as  his  frogs  lived 
thirty-six  days  after  the  operation.  According  to  Vincent,  extirpa- 
tion of  the  gland  of  guinea-pigs  did  not  affect  the  animal  in  any  way. 

PITUITARY   BODY, 

The  pituitary  body  (hypophysis  cereljri)  is  a  small,  reddish-gray, 
vascular  mass,  weighing  from  five  to  ten  grains.  It  is  oval  in  shape, 
situated  in  the  pituitary  fossa  of  the  sphenoid  bone,  and  is  connected 
with  the  end  of  the  infundibulum.  The  body  is  retained  in  position 
by  a  process  of  dura  mater  derived  from  the  inner  wall  of  the  cav- 
ernous sinus. 

Structure. — This  little  pituitary  body  is  very  vascular,  and  con- 
sists of  two  lobes,  separated  from  one  another  by  a  fibrous  stroma. 
The  two  lobes  differ  both  in  development  and  structure. 


372  PHYSIOLOGY. 

The  anterior  lobe  is  of  a  dark  yellowish-gray  color  and  resembles 
ill  microscopical  structure  the  tliyroid  body  and  suprarenal  bodies.  A 
canal  passes  through  the  anterior  lobe  to  connect  it  with  the  infun- 
dibulum. 

The  posterior  lobe  is  entirely  different  in  that  it  is  developed 
from  an  outgrowth  from  the  embryonic  brain,  and  therefore  is  ner- 
vous in  its  structure. 

Ablation  of  this  body  in  the  cat  produces  death  in  about  two 
weeks.  The  symptoms  resemble  very  much  those  that  follow  thy- 
roidectomy. Extracts  of  the  infundibular  part  elevate  the  arterial 
tension  by  a  constriction  of  the  arteries  and  slow  the  heart.  This 
substance  is  not  soluble  in  alcohol.  From  a  saline  decoction  of  the 
gland  there  was  obtained  an  alcoholic  precipitate  which  produced  a 
fall  of  arterial  tension;  so  that  there  seem  to  be  two  substances  in 
this  gland,  antagonizing  each  other  as  regards  arterial  tension.  Dis- 
ease of  this  gland  produces  the  condition  known  as  acromegaly,  in 
which  the  bones  of  the  face  and  limbs  become  hypertrophied.  It  is 
also  connected  with  giantism. 

EXTERNAL  SECRETION. 
THE  MAMMARY  GLANDS. 

The  mamma?,  or  breasts,  are  accessory  organs  of  the  generative 
system.  They  secrete  the  milk.  They  exist  in  the  male  as  well  as  in 
the  female,  but  only  in  a  rudimentary  condition  in  the  former.  In 
the  female  they  are  two  large,  hemispherical  eminences  situated 
toward  the  lateral  aspect  of  the  pectoral  region.  They  range  between 
the  third  and  seventh  ribs.  Before  puberty  they  are  of  small  size,  but 
enlarge  as  the  generative  organs  become  more  fully  developed.  They 
enlarge  during  pregnancy,  especially  after  delivery.  In  old  age  they 
become  atrophied. 

The  outer  surface  of  the  mammae  is  convex,  with  just  below  the 
center  a  small,  conical  eminence :  the  nipple.  The  surface  of  the 
nipple  is  dark-colored,  and  surrounded  by  an  areola  of  a  colored  tint. 
In  the  virgin  the  areola  is  of  a  delicate,  rosy  hue;  about  the  second 
month  after  impregnation  it  enlarges  and  also  acquires  a  darker 
shade  of  color.  The  color  deepens  as  pregnancy  advances;  in  some 
cases  it  becomes  dark  brown  or  even  black.  After  cessation  of  lacta- 
tion there  is  a  diminution  in  the  quantity  of  pigment,  but  the 
original  hue  is  never  regained.  Change  in  the  color  of  the  areola  is 
of  importance  in  determining  an  opinion  in  cases  of  suspected  first 
pregnancy. 


SECRETION. 


373 


The  nipple  is  a  conical  eminence  that  is  capable  of  erection  from 
mechanical  excitement.  This  is  mainly  produced  by  the  contraction 
of  its  unstriped,  muscular  tissue,  aided  by  its  numerous  blood-vessels. 
All  tend  to  give  it  an  erectile  structure.  The  nipple  is  perforated  by 
numerous  orifices:  the  apertures  of  the  lactiferous  ducts.  On  its 
surface  are  very  sensitive  papillae.  Near  the  base  of  the  nipple  and 
upon  the  surface  of  the  areola  are  numerous  sebaceous  glands.  These 
become  enlarged  during  lactation,  their  fatty  secretion  serving  as  a 
means  of  protection  during  the  act  of  sucking. 


Fig.  156. — Mammary  Gland  of  Human  Female.  (After  Liegeoir.) 
(From  Mills's  "Animal  Physiology,"  copyright,  1889,  by  D.  Appleton 
and  Company.) 

1,    Sinus,   or   dilatation   of   one   of  lactiferous    ducts.      2,    Extremities   of   the 
ducts.    3,  Lobules  of  gland.    4,  Nipple,  retracted  in  center.    5,  Areola. 


The  nipple  is  made  up  of  areolar  tissue  interspersed  with  num- 
erous blood-vessels  and  plain  muscular  fibers.  The  fibers  are  ar- 
ranged chiefly  in  a  circular  manner  around  the  base,  some  fibers,  how- 
ever, radiating  from  the  base  to  the  apex. 

Structure  of  the  Mammae. — The  mammae  consist  of  gland-tissue. 
Like  other  glands,  they  are  composed  of  large  divisions,  or  lohes. 


374  PHYSIOLOGY. 

which  in  turn  are  subdivided  into  lobules.  The  lobules  and  lobes  are 
held  together  by  means  of  fibrous  tissue,  while  between  the  lobes  are 
septa. 

The  mammary  gland-tissue,  in  general,  when  free  from  fibrous 
tissue  and  fat,  is  of  a  pale-reddish  color,  firm  in  texture,  and  circular 
in  form.  The  smallest  lobules  consist  of  a  cluster  of  rounded  vesicles, 
which  open  into  the  smallest  branches  of  the  lactiferous  ducts. 
These  small  ducts  unite  to  form  larger  ducts,  which  later  terminate 
in  a  single  canal.  This  latter  corresponds  with  one  of  the  chief  sub- 
divisions of  the  gland. 

These  main  excretory  ducts,  about  fifteen  or  twenty  in  number, 
are  termed  tubuli  lactiferi.  These  present  in  their  course  a  general 
convergence  toward  the  areola,  beneath  which  they  form  dilata- 
tions: ampullce.  These  dilatations  serve  as  small  reservoirs  for  the 
milk.  During  active  secretion  by  the  gland  the  milk  collecting  in 
them  distends  them.  Each  lactiferous  duct  is  of  an  average  diameter 
of  one  seventy-fifth  of  an  inch,  expanding  into  the  ampullae,  whose 
average  caliber  is  one-fourth  of  an  inch.  At  the  base  of  the  nipple 
the  ampulla!  become  contracted  again  to  pursue  a  straight  course  to 
its  summit.  Each  duct  pierces  the  nipple  by  a  separate  orifice,  whose 
opening  is  about  one-fiftieth  of  an  inch.  The  ducts  are  composed  of 
areolar  tissue  with  elastic  fibers  and  longitudinal  muscular  fibers. 
Their  mucous  lining  is  continuous  at  the  point  of  tlie  nipple  with  the 
integument.  They  are  lined  internally  by  short  columnar,  and,  near 
the  nipple,  by  flattened  epithelium. 

With  the  exception  of  the  nipple,  the  general  surface  of  the 
mamma  is  covered  with  fat.  The  latter  is  lobulated  by  sheaths  and 
processes  of  connective  tissue,  which  bind  the  skin  and  the  gland 
together  loosely.  It  is  by  this  same  manner  that  the  gland  is  fast- 
ened to  the  great  pectoral  muscle  beneath  it. 

Blood-vessels,  nerves,  and  lymphatics  are  plentifully  supplied  to 
the  mammary  glands. 

The  arteries  are  derived  from  the  thoracic  branches  of  the  axil- 
lary, the  intercostals,  and  internal  mammary.  The  veins  describe, 
by  their  frequent  anastomoses,  a  circle  around  the  base  of  the  nipple. 
This  has  been  called  by  Haller  the  circulus  venosus.  Prom  this 
branches  run  to  the  circumference  of  the  gland.  The  caliber  of  the 
contained  vessels,  as  well  as  the  size  of  the  glands,  may  be  increased 
during  pregnancy  and  lactation.  The  lymphatics  principally  run 
along  the  lower  border  of  the  pectoralis  major  muscle  to  the  axillary 


SECRETION. 


375 


glands  The  nerves  are  derived  from  the  supraclavicular  and  the 
intercostals.     No  secretory  nerves  of  the  manimge  exist. 

Each  gland-acinus,  or  vesicle,  consists  of  a  membrana  propria, 
surrounded  externally  with  a  network  of  branched  connective-tissue 
corpuscles.  Internally  there  is  a  somewhat  flattened  polyhedral  layer 
of  nucleated  secretory  cells.  The  size  of  the  lumen  of  the  acini  de- 
pends upon  the  secretory  activity  of  the  glands;  when  it  is  large  the 
vesicle  is  filled  with  milk  containing  numerous  refractive,  fatty 
granules. 

In  the  gland  of  a  woman  who  is  not  pregnant  or  suckling  the 
alevoli  are  very  small  and  solid.  They  are  filled  with  a  mass  of 
granular,  polyhedral  cells.  During  pregnancy  the  alveoli  enlarge, 
while  the  cells  undergo  rapid  multiplication.     With  the  beginning  of 


Fig.   157. — Dog's  ^lammary  Gland  in  First  Stage  of  Secretion. 
(Heidenhain.  ) 

a,   6,   Section  through  the  center  of  two  alveoli  of  the  mammary  gland,   the 
epithelial  cells  seen  in  profile,     c.  Surface  view  of  the  epithelial  cells. 


lactation  the  cells  in  the  center  of  the  alveolus  undergo  fatty  degen- 
eration and  are  eliminated  in  the  first  milk  as  colostrum-corpuscles. 
The  lining  cells  of  the  alveolus  remain  to  form  a  single  layer  of 
granular,  short,  columnar  cells.  Each  possesses  a  spherical  nucleus, 
and  is  attached  to  the  limiting  membrana  propria.  By  means  of 
metabolic  processes  within  the  protoplasm  of  the  cells  the  fats,  salts, 
milk-sugar,  etc.,  are  formed.  During  glandular  activity,  instead  of 
one.  two  or  more  nuclei  are  seen ;  the  well-formed  one  is  near  the 
base,  the  other  nearer  the  free  end  of  the  cell.  Near  the  border  of 
the  cell  are  seen  numerous  oil-globules  and  granules.  Some  of  the 
larger  oil-globules  are  seen  projecting  from  the  surface  of  the  cell 
as  if  about  to  be  extruded  from  it. 

In  addition  to  this,  a  division  of  the  cell  itself  takes  place:  a 
parting  of  the  cell-substance  with  a  nucleus  in  it.  The  daughter- 
cell  thus  east  off  passes  into  the  alveolus  to  form  a  part  of  the  milk. 


376  PHYSIOLOGY. 

The  secretion  of  milk  is  an  example  of  a  secretion  that  is  eminently 
the  result  of  the  metabolic  activity  of  the  secreting  cell.  The  blood 
is  the  original  fountain  of  the  milk,  but  it  becomes  milk  only  by  the 
action  of  the  cells  of  the  mammary  gland:  a  metabolism  of  those 
cells. 

Ottolenghi  has  found  in  the  active  mammary  gland  of  guinea- 
pigs  the  presence  of  "Ninsen's  globules,"  which  are  due  to  two 
causes:  first,  an  increase  of  the  nuclei  of  the  epithelium  of  the 
gland;  and  second,  an  infiltration  of  the  gland  cells  with  leucocytes. 
This  theory  is  opposed  to  that  of  Heidenhain,  and  makes  the  milk 
secretion  chiefly  a  disintegration  of  the  nuclei  of  the  epithelium  of 
the  gland  rather  than  a  breaking  up  of  the  protoplasm. 

Ottolenghi  also  saw  in  the  milk  glands,  with  islands  of  active 
gland  tissue,  other  islands  of  a  colostrum  type — a  type  of  relative 
rest. 


Fig.   158. — MamniHiy  Gland  of  the  Dog,  Second  Stage  of  Secretion. 
(Heidenhain.) 

Colostrum. — At  the  beginning  of  the  period  of  lactation  milk  is 
of  a  peculiar  character  and  has  received  the  name  of  colostrum. 
This  term  is  also  applied  to  the  milk  appearing  during  the  first  week 
after  confinement.  Colostrum  is  acid,  possesses  a  yellow  color,  which 
becomes  white  toward  the  fourth  day.  It  is  viscid  and  has  a  mean 
density  of  1.056.  It  contains,  in  addition  to  the  fat-globules,  colos- 
trum-corpuscles. These  are  the  degenerating  polyhedral  cells  which 
filled  the  vesicles  previous  to  lactation. 

I  have  found  that  infusion  of  dried  mammary  gland  decreases 
the  pulse  and  increases  arterial  tension.  The  blood-pressure  rises 
after  removal  of  the  main  vasomotor  center. 

Functional  Variations  in  Milk. — A  substantial  amount  of  nour- 
ishment augments  the  quantity  of  milk.  Drinks  have  the  same 
effect.  An  exclusive  meat  diet  augments  the  proportion  of  fat  in 
the  milk;  a  small  meat  allowance  in  a  mixed  diet  increases  casein 
and  diminishes  the  sugar.     A  vegetable  diet  diminishes  the  total 


SECRETION. 


377 


quantit}^,  lowers  the  amount  of  casein  and  butter,  but  augments  the 
proportion  of  sugar  of  milk.  A  diet  rich  in  fats  does  not  augment 
the  quantity  of  butter,  but  if  kept  up  too  long  it  diminishes  it. 
Atropine  and  potassium  iodide  dry  up  the  milk  secretion;  antipyrin 
is  said  to  have  a  similar  effect.  Jaborandi  increases  it.  Alcohol, 
frequently  given  in  the  shape  of  porter,  increases  the  secretion  of 
milk. 

THE  SWEAT=GLANDS. 

The  sweat-glands  are  the  organs 
which  furnish  the  means  for  the  elimina- 
tion of  a  large  portion  of  the  aqueous  and 
gaseous  materials  excreted  by  the  skin. 
They  are  found  in  almost  every  part  of  the 
integument,  being  particularly  numerous 
where  hairs  are  absent,  as  upon  the  palms 
and  soles.  Krause  found  the  smallest 
number  of  them  (400  for  each  square  inch) 
upon  the  back  and  buttocks;  the  greatest 
number  (2800  per  square  inch)  on  the  sur- 
face of  the  palm  of  the  hand  and  the  sole 
of  the  foot.  By  this  observer  it  was  cal- 
culated that  the  total  number  of  them  is 
2,400,000.  These  glands  may  become  hy- 
pertrophic (in  elephantiasis),  thereby  pro- 
ducing sudoriparous  tumors  upon  the 
cheek.     Atrophy  also  occurs. 

In  structuw  the  sweat-glands  are 
small,  lobular,  reddish  bodies.  Each  con- 
sists of  a  single,  convoluted  tube,  from 
which  mass  the  efferent  duct  proceeds  up- 
ward through  the  corium  and  cuticle.  It 
is  somewhat  dilated  at  its  extremity  and 
opens  upon  the  surface  of  the  cuticle  by 
an  oblique  valvelike  aperture.  The  effer- 
ent portion  of  the  duct  in  its  course  through  the  skin  presents  a 
corkscrew  arrangement  in  those  places  where  the  epidermis  is  thick. 

The  convoluted  or  coiled  portion  of  the  tube  is  the  place  where 
secretion  takes  place,  and  is  usually  known  as  the  secretory  part  of 
the  sweat-apparatus.  Here  the  tube  is  lined  by  a  single  layer  of 
clear,  nucleated,  cylindrical  epithelium.     Smooth  muscular  fibers  in 


'/■^^m^ 


Fig. 


159.— Sweat   Gland. 
(Hedon.) 


1,  Bpiderm.  2,  Malpighian 
layer.  3,  Derm.  4,  Papilla. 
5,  Gland  folded  on  itself.  6, 
Duct  of  gland.  8,  Opening  of 
duct.     9,  Subcutaneous  tissue. 


378  PHYSIOLOGY. 

the  larger  glands  are  arranged  longitudinally  along  the  tube.  Be- 
yond the  muscular  coat  is  the  basement-membrane;  so  that  the  duct 
has  a  definite  outline  and  exists  as  an  entity  that  is  distinct  from 
the  surrounding  tissues. 

The  distal  portion  of  the  tube  serves  the  simple  purpose  of  a 
conduit  for  the  passage  of  the  sweat-secretion  to  the  skin  surface. 
It  contains  no  muscular  fibers  or  basement-membrane.  There  is, 
however,  a  distinct  lumen  surrounded  by  several  layers  of  cubical 
cells;  so  that  by  some  authorities  this  portion  of  the  apparatus  is 
considered  to  be  but  an  opening  between  epidermal  cells. 

Glands  which  are  constantly  active,  as  are  the  sweat-glands, 
must  necessarily  require  a  very  liberal  blood-supply.  Each  coil  (the 
real  seat  of  secretion)  is  surrounded  by  a  network  of  capillaries, 
whose  arrangement  is  such  that  the  secretory  cells  are  easily  enabled 
to  obtain  the  watery  secretion  from  the  blood-stream. 

Nerves. — A  plentiful  supply  of  nerve-fibers  in  the  form  of  a 
nerve-plexus  ends  in  the  glandular  substance.  That  the  secretion  of 
sweat  is  not  a  mere  filtration  that  varies  according  to  the  blood- 
pressure,  but  a  process  dependent  upon  a  direct  action  of  the  nerve 
upon  the  gland-cell,  has  been  demonstrated  by  Oft.  In  experiments 
upon  cats  certain  changes  were  produced  in  the  cell-protoplasm  by 
changes  in  the  activity  of  the  nerve. 

In  the  cat  the  sciatic  was  cut  and  the  animal  kept  until  the 
fifth  day.  At  this  time  the  pads  of  the  feet  were  excised,  placed  in 
absolute  alcohol,  and  when  hard  enough  were  cut  into  sections, 
stained  with  carmine  solution,  and  mounted  in  glycerin. 

In  another  cat  the  sciatic  was  exposed  and  the  nerve  feebly 
irritated  for  a  period  of  two  and  one-half  hours,  when  the  pads  of 
the  feet  were  treated  in  the  same  manner. 

Sections  of  the  pads  of  the  feet  of  each  cat  were  then  examined 
microscopically.  It  was  found  that  the  irritated  cells  were  smaller 
than  the  resting  cells,  that  their  protoplasmic  contents  were  more 
granular  and  more  highly  tinged  with  carmine  solution,  although 
left  in  it  the  same  length  of  time  as  the  resting  cell.  These  facts 
have  been  confirmed  by  Renaut  in  the  horse's  glands. 

Sweat  is  the  secretory  product  of  the  sudoriferous  glands.  It 
is  discharged  in  a  continuous  fashion  upon  the  surface  of  the  skin, 
there  to  be  gotten  rid  of  as  vapor.  i\.s  long  as  the  secretion  is  small 
in  amount  it  is  evaporated  from  the  surface  at  once.  Because  of 
this  feature  it  is  termed  insensible  perspiration.  The  skin  is  supple, 
fresh,  and  without  any  appreciable  humidity. 


SECRETION. 


379 


Fi^.L 


Fuf.  Z, 


Fi^,3. 


Fig.   100. — Section  of  Sweat-glands  of  Cat. 

1,    Section   of  gland   five   days  after  section  of  sciatic  nerve.     2,   Gland  with 
sciatic   irritated   two   and   one-half   hours.     3,    Sweat-gland   in   normal   condition. 


380  .  PHYSIOLOGY. 

When,  however,  the  secretion  of  the  glands  is  increased  in  quan- 
tity or  its  evaporation  arrested,  drops  appear  upon  the  skin.  These 
drops  of  water  form  what  is  commonly  known  as  sweat.  During  this 
condition  the  skin  is  also  supple  and  soft,  but  is  humid.  There  often 
is,  in  fact,  a  visible  liquid. 

Sweat  is  a  more  or  less  transparent  liquid,  of  a  salty  flavor.  It 
is  constantly  acid  in  reaction  and  has  a  specific  gravity  of  1.004. 

The  acidity  is  due  to  acid  sodium  phosphate.  From  its  very 
ready  contamination,  it  is  impossible  to  obtain  sweat  in  a  pure  state. 

The  relation  of  the  sensible  and  insensible  perspirations  varies 
considerably  with  the  temperature  of  the  air.  In  round  numbers, 
the  total  amount  of  sweat  secreted  by  a  man  is  tivo  pounds  in  twenty- 
four  hours. 

The  quantity  of  solid  components  of  sweat  is,  on  the  average, 
1.0  per  cent.  It  may  descend  to  0.8  per  cent,  when  there  is  an 
increase  in  the  rapidity  of  the  secretion.  That  means  that  in  pro- 
fuse perspiration  it  is  the  water  which  acquires  the  predominance. 
However,  no  matter  what  the  celerity  of  the  perspiration,  there 
is  a  minimum  of  solid  components:  0.8  per  cent.  This  remains 
unchanged,  showing  that  the  sweat  is  a  primitive  secretion  in  char- 
acter. 

Sweat  contains  many  and  different  members  of  the  series  of  fat 
acids,  neutral  fats,  alkaline  sulphates  and  phosphates,  lactic  acid,  and 
urea.     Horse's  sweat  contains  albumin. 

The  different  strength  and  odor  peculiar  to  the  sweat  of  differ- 
ent animals  is  due  to  the  variety  and  abundance  of  the  volatile  fatty 
acids.  Of  these,  acetic,  formic,  and  butyric  prevail  in  general,  with 
capronic  and  caprillic.  To  their  prevalence  in  the  armpits  and  feet 
is  due  the  corresponding  intensity  of  odor. 

It  has  been  calculated  that  about  0.08  per  cent,  of  the  sweat  is 
urea.  It  may  be  increased  greatly  in  cholera,  by  reason  of  its  sup- 
pressed passage  through  the  kidneys.  There  is  often  observed  a 
crystalline  deposit  of  this  substance  upon  the  surface  of  the  body  in 
death  by  cholera. 

Carbonic  acid  and  traces  of  nitrogen  are  found  diffused  in  the 
sweat  and  so  eliminated  from  the  organism. 

Perspiration  is  especially  favored  by  the  elevation  of  the  bod,y- 
temperature;  by  the  wateriness  of  the  blood;  by  the  energetic  action 
of  the  vessels  of  the  heart;  by  increase  of  pressure  in  the  cutaneous 
vessels,  as  during  muscular  exercise,  etc. 


SECRETION.  381 

Drugs. — Certain  drugs  favor  sweating.  Such  are  pilocarpine. 
Calabar  bean,  strychnine,  picrotoxine,  muscarine,  nicotine,  camphor, 
and  the  ammonias.  Atropine,  and  morphine  in  large  doses,  diminish 
Ihe  secretion.  I  have  found  that  muscarine  and  pilocarpine  act  on 
the  peripheral  end  of  the  sudorific  nerves. 

Quinine,  iodine,  arsenic,  and  mercury,  when  introduced  into  the 
body,  reappear  in  the  sweat. 

Although  the  nerves  of  the  sweat-glands  are  not  anatomically 
separated  from  others,  yet  their  concurrence  in  the  secretion  is  evi- 
dent. In  cutting  the  cervical  sympathetic  in  a  horse  there  is  pro- 
duced unilateral  sweating  (Dupuy).  According  to  the  increased 
intensity  with  which  the  cervical  sympathetic  is  galvanically  excited 
through  the  skin  of  man,  there  follows  a  lowered  or  increased  per- 
spiration of  the  corresponding  side  of  the  face.  These  facts,  to- 
gether with  the  known  dilatation  of  the  cutaneous  vessels  in  profuse 
perspiration,  show  the  influence  of  the  vasomotor  nerves. 

Goltz  and  others  have  shown  that  by  exciting  the  nerve  of  a 
limb  the  perspiration  of  it  can  be  increased  through  the  action  of 
sudorific  nerve-fibers.  The  same  results  have  been  attained  even 
though  the  limb  has  been  previously  amputated  and  therefore  no 
longer  subject  to  circulation.  It  appears  that  the  vasomotor  and 
sudorific  nerve-fibers  run  in  the  nerves  by  themselves. 

Stimulating  in  man  a  motor  nerve, — such  as  the  tibial,  median, 
or  facial, — the  part  corresponding  to  the  active  muscles  would  per- 
spire, even  upon  the  side  not  excited.  Yulpian  and  Ott  have  made 
experiments  tending  to  prove  the  existence  of  inhibitory  fibers  of 
sweat. 

The  excretion  of  sweat  takes  place  through  vis  a  tergo,  aided  by 
the  concurring  contraction  of  the  interlaced  muscular  fibers  in  the 
glandular  glomerules.  Besides,  a  kind  of  aspiration  is  exercised  at 
the  mouth  of  the  gland  by  the  evaporation  of  the  liquid  which  arrives 
there.  It  is  for  this  latter  reason  that  air  saturated  with  vapor 
slackens  perspiration,  especially  when  the  other  causes  of  transjDira- 
tion  do  not  act  very  strongly. 

In  the  normal  state  the  sweat  and  urine  vary  in  quantity  with 
the  season ;  in  the  spring  the  sweat  predominates  over  the  urine,  in 
winter  the  reverse  is  true.  There  is  an  inverse  relation  between  the 
sweat  and  intestinal  secretions.  There  is  a  very  noticeable  balancing 
hetween  the  sweats  and  diarrhoea  of  phthisis. 

By  varnishing  the  body  death  is  caused.  This  does  not  occur  hj 
retention  of  poisonous  principles  in  the  Mood.     There  are  functional 


382  PHYSIOLOGY. 

iroubles,  the  most  remarkable  of  which  is  the  cooling  of  the  hody. 
This  cooling  is  due  to  vasodilatation,  and  is  the  cause  of  death. 

There  seems  to  be  a  very  steady  relation  between  the  amount  of 
moisture  exhaled  from  the  lungs  and  the  secretion  of  sweat.  It  is 
calculated  in  general  that  the  perspiration  is  double  that  of  the 
water  from  the  lungs  and,  on  an  average,  is  one  sixty-fourth  of  the 
weight  of  the  body. 

Suppression  of  Sweat  by  Cold. — All  pathologists  recognize  cold 
as  the  cause  of  numy  lesions  of  an  inflammatory  nature.  If  this  be 
true,  it  is  produced  not  by  suppression  of  sweat  alone.  It  is  prob- 
able that  there  is  a  transmission  of  impressions  by  the  skin-nerves 
to  the  nerve-centers.  These  impressions  generate,  by  an  obscure 
pathogenic  mechanism,  probably  bacterial,  the  inflammations  of  the 
viscera. 

Role  of  Sweat-secretions. — The  sweat  is  an  important  means  for 
the  elimination  of  water  and  alkalies. 

It  is  also  of  very  great  vise  in  the  excretion  of  fatty  volatile  acids, 
introduced  into,  or  formed  in,  the  organism.  It  is  able  to  supple- 
ment the  urinary  secretion,  for  the  skin  is  vicarious  for  the  kidneys. 
It  also  carries  off  medicines  and  poisonous  principles.  It  regulates 
animal  heat,  since  the  evaporation  of  the  water  of  sweat  cools  the 
body.  The  secretion  of  sweat  is  independent  of  the  circulation ;  how- 
ever, there  exists  a  relationship  between  them.  Thus,  an  abundance 
of  sweat  requires  a  full,  free  circulation.  As  the  salivary  glands  need 
a  flow  of  blood  to  furnish  materials  for  secretion,  so  do  the  sweat- 
glands. 

I  have  shown  elsewhere  that  the  sudorific  centers  are  in  the 
spinal  cord  and  that  their  fibers  run  in  the  lateral  columns.  The 
sweat-centers  are  excited  by  an  excess  of  CO,  in  the  blood  and  by  over- 
heated blood.  Camphor,  acetate  of  ammonium,  and  pilocarpine  ex- 
cite sweat  by  a  direct  action  on  the  centers.  Muscarine  excites  sweat 
by  a  local  action ;    atropine  arrests  it. 

Pathological. — Besides  the  components  mentioned,  biliary  pig- 
ment is  also  found  in  the  sweat  of  persons  having  jaundice;  sweat 
becomes  bitter  after  strong  doses  of  quinine  from  its  appearing  in 
this  medium  during  its  elimination  from  the  body.  The  sweat  of 
diabetes  is  found  to  be  sweetish,  although  the  presence  of  glucose  in 
it  has  not  been  definitely  determined.  The  red  pigmentation  some- 
times found  is  attributed  to  the  blood-globules,  crystals  of  w^hich 
were  found  in  the  sweat.  Hebra  saw  it  succeed  menstruation ;  but 
it  may  also  occur  in  serious  nervous  disease  and  in  yellow  fever.     In 


SECRETION.  383 

the  offensive  sweat  of  feet  there  are  found  leuein,  tyrosin,  valerianic 
acid,  and  ammonia. 

THE  SECRETION  OF  THE  URINE. 

In  a  perfectly  normal  being  the  problems  of  waste  and  repair 
are  balanced  to  a  nicety.  This  equilibrium  owes  its  maintenance  to 
the  proper  action  of  the  various  glands  of  the  economy,  whether  secre- 
tory or  excretory.  As  we  know,  the  tissues  of  the  body  are  bathed  in 
lymph  containing  in  solution  the  comjjounds  that  are  necessary  for 
their  nourishment :  proteids,  carbohydrates,  fats,  salts,  and  gases. 
By  reason  of  the  organism  exercising  its  various  functions,  waste 
follows  in  direct  proportion  to  the  activity  of  the  tissues.  The  worn- 
out  and  effete  materials  first  find  their  way  into  the  lymph  and  from 
it  into  the  blood-stream,  to  be  later  eliminated  from  the  economy, 
else  deleterious  results  will  follow  their  retention  in  the  body.  It  is 
by  the  selective  action  of  the  cells  of  the  various  glands  of  the  body 
that  these  useless  substances  are  removed  from  the  blood :  that  is, 
secreted  by  them  and  converted  into  such  form  as  to  be  readily  re- 
moved to  the  exterior  of  the  organism  by  excretory  processes.  In  the 
main,  the  products  to  be  removed  are  urea  and  allied  nitrogenous 
bodies,  carbon  dioxide,  salts,  and  water.  Most  of  the  water,  salts, 
urea,  and  allied  substances  are  eliminated  as  components  of  the  urine 
by  those  most  important  organs,  the  kidneys.  These  organs  are  of 
vital  importance,  since  nearly  all  of  those  waste-products  containing 
nitrogen  are  eliminated  in  the  urine. 

The  kidneys  secrete  the  urine.  Their  excretory  functions,  a  mat- 
ter of  everyday  observation,  represent  the  extent  of  their  external 
secretion ;  although  not  yet  definitely  settled,  the  consensus  of  opinion 
leans  toward  tlie  kidneys  possessing  an  internal  secretion  as  well. 

Morphology  of  the  Urinary  Apparatus. — The  secretory  organs  of 
the  urine  are  the  l-idnei/s.  They,  two  in  numl)er.  are  compound  tubu- 
lar glands,  situated  in  the  back  part  of  the  abdomen.  The  kidneys 
are  extraperitoneal  organs,  lying  behind  the  peritoneum  and  resting 
upon  the  lumbar  portion  of  the  diaphragm  and  the  anterior  layer  of 
the  lumbar  fascia.  The  upper  borders  of  the  kidneys  touch  a  plane 
that  is  on  a  level  with  the  upper  l)order  of  the  twelfth  dorsal  vertebra; 
their  lower  extremities  are  on  a  level  with  the  third  luml)ar  vertebra. 
The  right  kidney  is  usually  somewhat  lower  than  the  left,  probably 
because  of  the  pressure  exerted  by  the  liver,  against  whose  lower  sur- 
face the  kidney  rests.  In  front  it  is  in  relation  with  the  liver,  the 
descending  portion  of  the  duodenum,  and  the  hepatic  flexure  of  the 


384 


PHYSIOLOGY. 


colon;  the  left  kidney  lies  in  relation  with  the  fundus  of  the  stom- 
ach, the  tail  of  the  pancreas,  and  the  descending  colon.  Superiorly 
lie  the  suprarenal  bodies.  The  kidneys  are  incased  in  a  variable  quan- 
tity of  fat  and  loose  areolar  tissue,  to  which  has  been  given  the  name 
perirenal  fat. 

The  kidneys  are  firm  organs,  of  variable  color,  between  light  red 
and  bluish,  according  to  the  degree  of  congestion;  each  kidney 
weighs  about  four  and  one-lialf  ounces.     In  shape  they  resemble  a 


Fig.  161. — Relations  of  the  Kidney.      (After  Sappey. ) 

1,  1,  The  two  kidneys.  2,  2,  Fibrous  capsules.  3,  Pelvis  of  the  kidney. 
4,  Ureter.  5,  Renal  artery.  6,  Renal  vein.  7,  Suprarenal  body.  8,  8,  Liver 
raised  to  show  relation  of  its  lower  surface  to  right  kidney.  9,  Gall-bladder. 
10,  Terminus  of  portal  vein.  11,  Origin  of  common  bile-duct.  12,  Spleen 
turned  outward  to  show  relations  with  left  kidney.  13,  Semicircular  pouch 
on  which  the  lower  end  of  the  spleen  rests.  14,  Abdominal  aorta.  15,  Vena 
cava  inferior.  16,  Left  spermatic  vein  and  artery.  17,  Right  spermatic  vein 
opening  into  vena  cava  inferior.  18,  Subperitoneal  fibrous  layer  or  fascia 
propria  dividing  to  form  renal  sheath.  19,  Lower  end  of  quadratus  lumborum 
muscle. 

bean,  their  length  being  double  their  width ;  each  kidney  is  about 
four  inches  in  length,  two  inches  in  width,  and  one  inch  in  thicloiess. 
The  internal  border  of  each  kidney  is  concave,  the  concavity 
being  directed  slightly  forward  and  downward.  This  portion  of  the 
kidney  is  divided  by  a  deep,  longitudinal  fissure,  bounded  by  a  prom- 
inent anterior  and  posterior  lip.     The  fissure  is  known  as  the  hilus, 


SECRETION.  385 

and  allows  of  the  passage  of  the  vessels,  nerves,  and  ureter  to  and 
from  the  substance  of  the  kidney.  Just  within  the  hilus  is  a  dilated 
fossa  known  as  the  sinus^  which  contains  the  renal  artery,  the  vein, 
and  the  pelvis  of  the  kidney.  The  relation  of  the  structures  passing 
in  and  out  of  the  hilus  from  before  backward  are :  vein  in  front, 
artery  in  the  middle,  and  the  duct,  or  ureter,  behind  and  toward  the 
lower  part.  By  keeping  in  mind  these  relations  one  will  be  able  to 
distinguish  the  right  from  the  left  kidney  after  their  removal  from 
the  body. 

In  the  funnel-shaped  cavity  of  the  renal  pelvis  is  the  ureter. 
From  the  kidney  it  passes  over  the  psoas  muscle,  converging  toward 
that  of  the  opposite  side  to  cross  the  external  iliac  artery  and  vein. 
It  opens  obliquely  into  the  base  of  the  urinary  bladder.  In  females 
the  ureter  embraces  the  neck  of  the  uterus.  The  ureters  have  an 
average  length  of  eighteen  inches  and  a  lumen  which  averages  that  of 
a  goose-quill.  Just  before  piercing  the  bladder-wall  the  lumen  of 
the  ureter  becomes  appreciably  smaller. 

The  urinary  hladder,  situated  between  the  symphysis  pubis  and 
the  rectum  in  man,  between  the  symphysis  and  the  uterus  in  woman, 
is  held  in  position  by  the  urachus  and  lateral  ligaments.  Its  base 
rests  upon  the  perineum  and  anterior  wall  of  the  rectum  in  man, 
upon  the  anterior  wall  of  the  vagina  in  woman.  From  the  base  of 
the  bladder  the  urethra  takes  its  origin. 

The  opening  for  the  latter  bears  such  a  relation  to  the  entrance 
into  the  bladder  of  the  two  ureters  that  there  is  formed  the  vesical 
triangle.  The  openings  for  the  ureters  are  about  sixty  millimeters 
apart. 

The  capacity  of  the  bladder  varies  with  its  extensibility,  so  that 
it  is  possible  for  the  viscus  to  be  so  distended  that  its  upper  border 
may  reach  the  umbilicus  or  even  the  epigastric  region.  Ordinarily 
the  capacity  in  both  sexes  is  about  a  pint. 

The  bladder  receives  its  hlood-supphj  from  the  branches  of  the 
anterior  trunk  of  the  internal  iliac.  The  hjmpliatic  vessels  communi- 
cate with  the  lumlDar  ganglia.  The  nerves  are  derived  from  the  sym- 
pathetic, sacral,  and  probably  some  fibers  from  the  pneumogastric 
also. 

General  Structure  of  the  Kidney. — Beneath  the  perirenal  fat  lies 
the  proper  tunic,  or  covering,  of  the  kidney,  commonly  called  the 
capsule.  In  health  it  is  a  smooth,  thin,  but  tough,  fibrous  covering, 
closely  adherent  to  the  organ,  but  from  which  it  can  be  readily 
stripped.     By   reason  of  this   separation,  however,   fine   connective- 

25 


386 


PHYSIOLOGY. 


tissue  processes  and  minute  blood-vessels  are  torn  which  have  served 
as  a  means  of  attachment  for  the  capsule.  The  denuded  kidney  pre- 
sents a  smooth,  even  surface  of  a  deep-red  color. 

For  a  proper  naked-eye  study  of  the  kidney  the  organ  nmst  be 
divided  longitudinally  from  the  hilus  to  its  outer  border,  and  the  fat 
and  areolar  tissue  must  be  removed  from  the  vessels  and  ureter.  It 
will  at  once  be  seen  that  the  kidney  is  composed  of  a  cavity,  somewhat 

1 


Fig.   1G2. — Section  of  Kidney.      (Laxdois. ) 

1,  Cortex.  1',  Medullary  rays.  1",  Labyrinth.  3,  Medulla.  2',  Papillary 
portion  of  medulla.  2",  Bouniary  layer  of  medulla.  4,  Fat  of  renal  sinus. 
5,  Artery.     A,   Branch  of  renal  artery.     V,   Ureter.     C,   Renal  calyx. 

centrally  located,  and  the  jmrenchyriia  of  the  organ,  nearly  surround- 
ing the  central  cavity.  This  compartment,  as  before  stated,  is  termed 
the  sinus,  and  is  lined  by  a  continuation  of  the  fibrous  covering  of  the 
kidney.  It  is  through  the  hilus  that  this  fibrous  covering  j^asses,  as 
do  the  renal  vessels  and  ureter. 

The  ureter,  upon  entering  the  sinus,  is  expanded  into  a  funnel- 
shaped  sac,  the  pelvis.     The  pelvis  soon  divides  into  several  branches 


SECRETIOX. 


387 


Fig.  163. — Diagram  of  the  Course  of  Two  Uriniferoiis  Tubules. 
(Landois.) 

1,  Malpighian  tuft  surrounded  by  Bowman's  capsule.  2,  Constriction  on 
neck.  3,  Proximal  convoluted  tubule.  4,  Spiral  tubule.  5,  Descending  limb 
of  Henle's  loop-tube.  6,  Henle's  loop.  9,  Wavy  part  of  ascending  limb.  10, 
Irregular  tubule.  11,  Distal  convoluted  tubule.  12,  First  part  of  collecting 
tube.  13,  Straight  part  of  collecting  tube.  A,  Cortex.  B,  Boundary  zone.  C 
Papillary  zone. 

of  smaller  size,  and  these  immediately  subdivide  into  from  eight  to 
twelve  infundibula,  or  calyces,  from  their  resemblance  to  cups.  Into 
each  calyx  there  projects  the  point  or  extremity  of  a  renal  jDyramid. 
The  blood-vessels  lie  within  the  sinus,  between  its  wall  and  the  exte- 


388 


PHYSIOLOGY. 


rior  of  tlic  pelvis,  before  subdividing  and  entering  tlie  parcncbyma  of 
the  organ. 

Tlie  parencliyma  is  seen  to  be  composed  of  two  portions,  an 
external,  investing  cortical  portion,  and  an  inner  medullary,  or  pyra- 
midal, portion. 

The  cortex  is  light  brown  in  color,  granular,  and  very  friable. 
The  granuhir  aspect  is  due  to  the  presence  of  Malpighian  corpuscles, 
which  are  separated  at  regular  distances  by  medullary  rays,  or  striae, 
which  give  to  the  cortex  a  radiate  appearance.  The  boundary  zone 
is  darker,  and  also  striated  from  blood-vessels  and  uriniferous  tubules. 
It  is  through  this  portion  that  arteries  and  nerves  enter  and  veins 
and  lymphatics  pass  from  the  kidney. 


Fig.  164.      (Landois.) 

II.  Bowman's  capsule  and  glomerulus,  a,  Vas  afferens.  r,  Vas  eflerens. 
fc,  Endothelium  of  the  capsule,  c.  Capillary  network  of  the  corte.x.  /(,  Origin 
of  a  convoluted  tubule. 

III.  "Rodded  cells"  from  a  convoluted  tubule.  2,  Seen  from  the  side,  with 
g,   inner  granular  zone.     1,   Seen   from  the  surface. 

IV.  Cells   lining  Henle's   looped   tubule. 

V.  Cells   of    a   collecting   tube. 

VI.  Section  of  an  excretory  tube. 


The  medulla  is  composed  of  from  eight  to  twelve  pyramids,  or 
cones,  of  pale-red,  striated  tissue,  known  as  the  pyramids  of  Mal- 
pighi;  their  number  depends  upon  the  number  of  lobes  composing 
the  organ  during  the  foetal  state.  It  is  the  apices  of  these  cones 
which  dip  down  into  the  calyces  of  the  pelvis. 

Minute  Anatomy. — The  kidneys  consist  of  numerous  tubular 
glands  intimately  united  together.  The  tubes,  known  as  tuhuli  uri- 
niferi,  take  their  origin  in  the  labyrinth  of  the  cortex  as  distinct 
glolmlar  dilatations,  each  of  which  is  known  as  Bowman's  capsule. 


SECRETION. 


389 


The  capsule  surrounds  a  small,  red,  spherical  hody  known  as  the 
glomerulus,  or  Malpighian  corpuscle,  after  Malpighi,  its  discoverer. 
The  capsule,  about  one  one-hundredth  of  an  inch  in  diameter,  is  con- 
stricted at  its  neck  to  form  a  tube.  Beyond  this  constriction  the 
tube  pursues  a  very  convoluted  course  through  a  considerable  extent 
of  the  cortical  area,  as  the  tuhulus  contortus,  which  is  about  one  six- 
hundredth  of  an  inch  in  diameter.  Soon  the  convolutions  disap- 
pear to  give  place  to  a  more  or  less  spiral  tube  as  it  approaches  the 
medulla:  spiral  tube  of  Schachoira. 


Fig.  165. — Longitudinal  Section  of  a  Malpighian  Pyramid.      (Landois.) 


7i,  Cortex,  i.  Boundary  or  marginal  zone,  k,  Papillary  zone.  PF,  Pyra- 
mids of  Ferrein.  RA,  Branch  of  renal  artery.  RV,  Lumen  of  renal  vein 
receiving  an  interlobular  vein.  VR,  Vasa  recta.  PA,  Apex  of  renal  papilla. 
h,  b,  Embrace  the  bases  of  the  renal  lobules. 

At  the  boundary-line  between  cortex  and  medulla  the  tulie 
becomes  suddenly  smaller  and  is  now  perfectly  straight,  forming 
the  descending  limb  of  Henle's  loop,  dipping  down  for  a  consideral^le 
distance  into  the  pyramid.  By  the  sudden  changing  of  its  course 
backward,  but  still  paraUel  witli  its  original  course,  there  is  formed 
the  loop  of  Ilenle.  which,  continued  upward  to  the  cortex,  constitutes 
the  ascending  limb  of  Ilenle's  loop.     x\scending  into  the  cortex  it 


390 


PHYSIOLOGY. 


Fig.  16G. — Blood-vessels  and  Uriniferous  Tubules  of  the  Kidney 
( Semidiagrammatic ) .      (  Landois.  ) 

A,  Capillaries  of  the  cortex.  B,  Of  medulla,  a,  Interlobular  artery.  1, 
"Vas  affereas.  2,  Vas  efferens.  r,  e,  Vasa  recta,  c,  Venoe  rectas.  v,  v.  Inter- 
lobular vein,  i,  i,  Bowman's  capsule  and  glomerulus,  x,  x,  Convoluted  tubules. 
/,  t,  Henle's  loop,    o,  o,  Collecting  tubes.     O,  Excretory  tube. 

tecomes  dilated,  irregular,  and  angular, — zigzag, — which  ends  in  the 
distal  convoluted  tube,  finally  to  terminate  in  a  short  curved  tube^ 
which  empties  into  the  straight,  or  collecting,  tube. 


SECRETIOX.  391 

The  collecting  tubes,  as  they  run  toward  the  medulla  of  the  kid- 
ney, unite  with  other  distal  convoluted  tubules.  They  also- unite  at 
acute  angles  with  adjacent  collecting  tubes  finally  to  pass  to  the 
papillge.  The  loops  of  Henle  and  the  collecting  tiibes  constitute  the 
tuhuli  recti.  Each  uriniferous  tubule  is  thus  completely  isolated  as 
far  as  the  Junction  of  the  distal  contorted  tubes  with  the  collect- 
ing tube. 

A  portion  of  the  loops  of  Henle  and  the  upper  part  of  the  col- 
lecting tubes  form  the  little  cones  in  the  cortex,  visible  to  the  eye 
and  known  as  the  pyramids  of  Ferrein. 

The  Malpighian  corpuscle  consists  of  a  spherical  plexus  or  knot 
of  blood-vessels,  the  glomerulus,  which  is  inclosed  in  the  dilated  end 
of  the  urinary  tubule,  known  as  the  capsule  of  Bowman.  As  the 
capsule  has  been  infolded  by  the  glomerulus  being  pushed  into  it  (as 
one  would  infold  the  end  of  the  finger  of  a  glove  by  the  tip  of  one's 
finger),  it  follows  that  the  capsule  consists  of  two  layers.  The 
internal  one,  covering  the  glomerulus  closely,  is  formed  of  cubical 
ce.^ls,  while  the  external  one,  formed  of  flat,  polygonal  cells,  passes 
on  ii^to  the  neck  and  thence  forms  the  wall  of  the  convoluted  tubule. 
The  cells  in  this  portion  of  the  tube  are  shaped  like  a  cone,  the 
narrow  end  being  directed  toward  the  lumen  of  the  vessel;  owing 
to  the  fine,  longitudinal  lines  upon  each  cell,  it  has  a  rodlike  appear- 
ance: Todded  cell. 

The  Blood-vessels. — The  renal  artery  divides  at  the  hilus  into 
four  or  five  branches.  The  four  or  five  main  branches  continue  to 
divide  and  subdivide  and  so  pass  into  the  parenchyma  of  the  organ. 
They  course  between  the  papilla3  to  run  up  to  the  boundary  between 
the  medulla  and  cortex.  Here  the  vessels  bend  at  right  angles  to 
form  a  series  of  loops  or  arches,  their  convexity  toward  the  cortex 
of  the  kidney.  From  the  convex  sides  of  the  arches  there  spring 
vessels  at  regular  intervals  termed  interlolular,  or  radiate,  arteries. 
They  sometimes  run  up  so  as  to  divide  the  cortex  into  small  lobules, 
coursing  singly  between  each  two  medullary  rays.  These  radiate 
arteries  give  off  numerous  small  branches  which  run  at  right  angles, 
each  one  entering  a  Malpighian  corpuscle.  It  is  usual  for  the  point 
of  entrance  of  the  artery  to  be  diametrically  opposite  the  point  of 
origin  of  the  urinary  tubule.  These  last-named  vessels,  the  vasa 
afferentia,  break  up  into  very  fine  vessels  within  the  capsule  to  con- 
stitute the  glomerulus.  They  are  supported  by  connective  tissue, 
and  form  a  veritable  tuft  of  capillary  vessels.  It  is  of  interest  to 
note  that   each  glomerulus  is   covered   by   a  single   layer  of   flat. 


392  PHYSIOLOGY. 

lUK'lcatcd,   e])itlic'lial    ccJIs,   tlie.se   even    di])piii<r  down   between   the 
capillaries. 

From  the  center  of  tlie  glomerulus  there  proceeds  a  vessel  that 
is  somewhat  smaller  tlian  the  afferent  vessel,  known  as  the  efferent 
vessel;  it  is  a  vein,  and  leaves  the  capsule  very  close  to  the  point 
of  entrance  of  the  vas  afferens. 

The  efferent  vessel  also  divides  to  form  a  secondary  capillary 
network,  the  renal  portal  system,  with  elongated-meshes  in  the  situa- 
tion of  the  pyramids  of  Ferrein;  from  this  plexus  arise  the  inter- 
lobular veins  which  run  parallel  to  the  interlobular  arteries. 

The  m,edulla  of  the  kidney  receives  its  arterial  supply  from  the 
arterice  redce;  these  latter  are  vessels  which  spring  either  from  the 
arterial  arches  or  from  the  interlobular  arteries.  According  to  some 
authors,  they  may  be  derived  from  the  afferent  vessels  of  the  deepest 
and  largest  glomeruli.  Within  the  pyramids  the  arterige  rectae 
divide  and  subdivide  to  form  a  plexus  of  capillaries  which  eventually 
merge  into  the  vencv  rectce,  to  empty  into  the  venous  trunks  at  the 
boundary  between  the  medulla  and  cortex. 

The  renal  veins  arise  from  three  sources:  (1)  the  venous  plexus 
beneath  the  capsule,  (2)  the  plexus  around  the  tubuli  contorti,  and 
(3)  the  plexus  located  near  the  apices  of  the  pyramids.  Within  the 
sinus  the  larger  branches  from  these  plexuses  inosculate  to  form  the 
renal  veins,  which  pass  through  the  hilus  to  empty  into  the  inferior 
vena  cava. 

The  vasa  recta  circulation  is  of  prime  importance  in  that  it 
forms  a  sidestream  through  which  much  blood  may  pass  without 
being  compelled  to  traverse  the  glomerulus.  It  is  very  apparent 
that  this  circulation  is  highly  useful  in  conditions  of  kidney  conges- 
tion as  a  sidestream. 

Three  kinds  of  capillaries  are  found  within  the  kidney:  (1) 
glomerular,  (2)  efferent  capiUaries,  and  (3)  capillaries  of  the  vasce 
recta;.     The  kidney,  for  its  size,  is  abundantly  supplied  with  blood. 

Lymphatics. — The  kidneys  are  richly  supplied  wath  lymphatics, 
occurring  as  slits.  The  renal  lymphatics  terminate  in  the  lumbar 
lymphatic  glands. 

Nerves. — The  nerves  of  the  kidney  accompany  its  blood-vessels, 
ganglionic  plexuses  being  numerous.  They  are  from  the  renal 
plexus,  coming  originally  from  the  solar  plexus. 


SECRETIOX.  393 

Physical  Properties  and  Chemical   Composition  of  the   Urine. 

The  analytical  study  of  the  urine  is  of  great  value  to  the  physi- 
cian and  surgeon  because  of  the  knowledge  which  it  gives  concern- 
ing the  j^rocesses  of  metabolism  occurring  within  the  body.  The 
nature  and  amount  of  the  various  end-products  of  metabolism  are 
carefully  investigated  as  they  occur  in  the  urine,  whether  they  be 
normal  or  pathological.  From  these  investigations  corresponding 
conclusions  are  drawn. 

Neutral  substances  are,  normally,  either  absent  or  present  in 
but  minutest  quantities.  All  of  the  important  and  more  abundant 
constituents  of  normal  urine  are  either  basic  or  acid  in  reaction. 
These  bases  and  acids  must,  therefore,  enter  into  various  combina- 
tions, making  the  urine  a  solution  of  salts.  The  quantity  of  separate 
ingredients  found  analytically  might  lead  the  observer  to  consider 
the  metabolic  processes  as  pathological,  yet  in  solution  perfectly  nor- 
mal compounds  are  formed  by  these  same  components.  The  error 
is  due  to  the  inability  to  study  the  properties  of  the  urine  as  a  com- 
plex unit:  the  effects  certain  components  have  on  others,  their 
avidity  for  one  another,  and  the  consequent  equilibrium  established. 

The  Urine. — The  normal  human  urine,  recently  passed,  is  a  clear 
liquid  of  a  straw  color.  It  has  an  average  specific  gravity  of  1.020, 
is  of  aromatic  odor,  and  a  salty  bitter  flavor.  In  reaction  it  is  acid; 
only  in  pathological  conditions  does  it  become  neutral  or  alkaline. 

Eeceding  from  the  temperature  of  about  100°  F.,  which  is  pro- 
per to  it  in  the  act  of  passing,  it  loses  its  aromatic  odor  and  acquires 
a  peculiar  odor,  described  as  urinous.  In  healthy  persons  it  has 
been  seen  to  be  phosphorescent  during  micturition,  probably  from 
the  liberation  of  phosphorus  by  its  salts.  In  cooling,  urine  becomes 
turbid,  with  a  small  cloud  suspended  in  the  thickness  of  the  liquid, 
formed  from  the  epithelium  of  the  uriniferous  tubules.  It  leaves, 
besides,  especially  if  very  much  colored,  sediments  of  different 
appearance,  according  to  the  varying  composition. 

The  quantity  of  urine  secreted  by  the  kidneys  of  a  healthy  adult 
man  in  twenty-four  .hours  ranges  from  1200  to  1700  cubic  centi- 
meters, or  about  50  ounces ;  in  females  the  quantity  is  less.  During 
sleep  the  amount  secreted  is  less  than  at  other  times,  so  that  the 
minimum  secretion  is  placed  between  2  and  4  a.  m.  and  the  maximum 
from  2  to  4  P.  M. 

While  the  average  daily  secretion  is  placed  at  50  ounces,  yet  it 
must  be  borne  in  mind  that  this  quantity  is  not  fixed,  but  may  be 
very  variable,  dependent  upon  numerous  conditions. 


394  rilYSIOLOGY. 

The  amount  of  urine  is  diminished  by  reason  of  profuse  sweat- 
ing, extensive  diarrlia'a,  thirst,  diminution  in  blood-pressure,  after 
severe  ha3niorrhage,  and  in  some  forms  of  kidney  disease. 

Increase  in  urinary  secretion  (polyuria)  is  produced  by  an  in- 
crease in  blood-pressure,  by  imbibing  excessive  draughts  of  liquids, 
by  any  condition  whereby  the  cutaneous  blood-supply  is  diminished 
(cold  will  do  this).  Polyuria  is  likewise  produced  by  the  administra- 
tion of  drugs  which  raise  arterial  tension,  as  digitalis  and  alcohol, 
and  by  caffeine  and  sparteine,  which  stimulate  the  renal  cells. 

The  influence  of  the  nervous  system  upon  the  secretion  of  urine 
is  very  beautifully  demonstrated  by  cases  of  hysteria.  Hysterical 
patients  void  excessive  amounts  of  a  very  pale,  watery  urine. 

The  specific  gravity,  as  previously  stated,  averages  1.020;  that 
is,  the  mean  between  1.015  and  1.025.  The  specific  gravity  varies 
inversely  to  the  quantity  excreted.  When  for  any  reason,  not  patho- 
logical, there  is  polyuria,  the  mark  drops  proportionately,  register- 
ing as  low  as  1.002.  As  a  result  of  profuse  sweating  and  abstinence 
from  licjuids,  the  mark  may  reach  1.035  in  healthy  individuals. 

Acidity. — The  acidity  of  the  urine  is  chiefly  due  to  acid  phos- 
phate of  sodium.  There  are  two  tides  in  the  acidity  of  the  urine. 
During  digestion  the  formation  of  the  hydrochloric  acid  in  the 
stomach  frees  certain  bases  in  the  blood,  which,  when  excreted, 
diminish  the  acid  reaction  of  the  urine.  This  is  called  the  alkaline 
tide.  The  acid  tide  is  after  a  fast,  and  hence  occurs  early  in  the 
morning. 

Ordinarily  it  should  be  remembered,  when  taking  the  specific 
gravity  of  urine,  that  anything  below  1.010  should  at  once  excite 
suspicion  of  polyuria,  with  probably  albumin;  when  above  1.030, 
diabetes  mellitus  or  some  febrile  condition  may  be  present. 

The  urinonieter  is  the  instrument  used  to  ascertain  the  density 
of  any  given  sample  of  urine,  and  is  so  graduated  that,  when  floating 
in  distilled  water,  it  registers  0  degrees,  by  which  is  meant  1000. 
The  urine  is  placed  in  a  tall,  cylindrical  glass  of  proper  width  so 
that  the  urinometer  will  not  adhere  to  its  sides.  After  cessation  of 
the  oscillations  of  the  instrument,  the  observer  carefully  sights  along 
the  surface  of  the  urine  to  note  the  number  registered.  This  pre- 
caution is  taken  because  the  capillarity  along  the  stem  of  the  instru- 
ment causes  the  urine  to  rise. 

The  urine  is  composed  of  ivater  in  the  average  proportion  of  9(5 
per  cent.,  and  of  substances  dissolved  in  it  in  the  proportion  of  4 
per  cent. 


SECRETION. 


395 


Among  the  "substances  dissolved"  in  urine  we  find:  urea,  uric, 
hippuric,  lactic,  and  oxalic  acids,  and  ammonia;  also  creatin,  chlo- 
rides, sulphates,  phosphates,  with  the  l)ascs — potassium,  sodium,  cal- 
cium, and  magnesium. 

Urea  (C0[NH2],)  is  the  diamide  of  CO^;    that  is,  a  carbamide. 

Urea  greatly  prevails  over  the  other  constituents  of  the  urine, 
since  in  normal  urine  it  forms  nearly  one-half  of  the  solids.  Nearly 
one-half  of  urea  is  nitrogen.  It  is  the  principal  representative  of 
the  waste  of  the  nitrogenous  tissues. 

Urea  is  inodorous,  fresh,  bitter,  neutral,  very  soluble  in  water 
and  alcohol,  but  almost  insoluble  in  ether.     It  crystallizes  quickly 


Fig.  167. — Urea  from  Human  Urine.  (Funke. )  (From  Tiger- 
stedt's  "Human  Physiology,"  copyright,  1906,  by  D.  Appleton  and  Com- 
pany. ) 

into  needles;  slowly,  into  quadrangular  prisms  of  the  rhombic  sys- 
tem. Urea  fuses  and  decomposes  at  248°  F.,  with  the  development 
of  ammonia. 

Urea  is  very  rich  in  nitrogen.  The  nitrogen  that  finds  its  way 
from  the  body  through  the  urine  as  a  vehicle  amounts  to  about  15 
grams  in  twenty-four  hours.  This  represents  practically  all  of  the 
nitrogenous  waste  of  the  economy,  since  less  than  1  gram  finds  egress 
from  all  other  channels  taken  collectively.  The  total  amount  of 
nitrogen  is  estimated  by  the  Kjeldahl  process. 

x\mong  the  combinations  with  acids  and  bases  of  which  urea 
is  capable,  those  with  nitric  and  oxalic  acids  are  important.  It  is 
precisely  these  which  are  most  commonly  employed  in  the  extraction 
of  urea.  With  nitric  acid,  nitrate  of  urea  is  formed,  which  crystal- 
lizes in  lozenge-shaped  crystals.     With  oxalic  acid,  urea  forms  urea 


396  niY.SIOLOGY. 

oxalate,  and  crystallizes  into  flat  or  prismatic  bodies.  Both  types 
of  crystals  may  very  readily  be  demonstrated  by  placing  crystals  of 
urea  beneath  cover-glasses  and  allowing  drops  of  nitric  and  oxalic 
acids,  respectively,  to  flow  beneath  the  cover-glasses.  After  some 
little  time  crystals  of  the  respective  types  will  be  seen  to  form. 
Besides  being  free,  nrea  is  found  combined  in  the  urine  with  sodium 
chloride. 

Decomposition  of  Urea. — When  urea  is  heated,  vapors  of 
ammonia  are  evolved.  Urine  is  also  subject  to  an  alkaline  fermenta- 
tion, due  to  the  micrococcus  urege.  This  generally  follows  the  acid 
fermentation,  but  may  take  place  without  it,  in  the  bladder  as  well 
as  outside.  This  fermentation  is  accomplished  by  decomposition  of 
the  urea  into  carbonate  of  ammonia.  By  virtue  of  this  the  urine  is 
strongly  darkened,  becomes  alkaline,  putrescent,  and  forms  a  film  of 
bacteria  on  its  surface.     Urinals  always  have  an  ammoniacal  odor. 


'^ 


Fig.    IfiS. — Micrococcus    Uieiie.      X  500.      (After    vox    Jaksch.) 
Hypobromite  of  soda  decomposes  urea  as  follows: — 

/XH.  +  SXaBrO  =  CO,  -f  X,  +  2H.,0  +  3XaBr 

Urea.  Sodium  Carbonic.       Nitrogen.  Sodium 

hypobromite.  acid  bromide. 

Upon  this  reaction  depends  an  estimation  of  the  amount  of  urea 
present  in  a  sample  of  urine.  The  calculation  is  made  in  units  of 
nitrogen-gas,  which  gas  rises  in  small  bubbles  to  be  collected  and 
measured. 

The  constituents  of  urine  are  not  actually  formed  in  the  kidney 
itself,  as  laile  is  formed  in  the  liver,  but  are  formed  elsewhere.  The 
kidney  is  simply  the  place  where  the  constituents  are  picked  out  from 
the  blood  and  eliminated  from  the  body. 

Muscular  exercise  has  but  a  slight  effect  on  the  amount  of  urea 
excreted;  this  is  in  striking  contrast  to  the  quantity  of  carbonic  acid 
that  accompanies  muscular  exertion  to  find  exit  in  the  expired  air. 
Muscle-work  falls  upon  the  carbon  rather  than  upon  the  nitrogen  of 
the  muscle-substance. 

Quantity  of  Urea. — The  quantity  of  urea  excreted  daily 
varies,  but  mav  be  averaged  as  500  grains.     Aecordincr  to  Tschlenofl", 


SECRETION.  397 

after  a  meal  rich  in  proteids,  which  stimulate  proteid  metabolism, 
there  are  two  maxima  in  its  excretion.  The  first  takes  place  at  the 
third  or  fourth  hour  and  the  second  at  the  sixth  or  seventh  hour. 
The  urea  comes  from  proteid  metabolism,  and  not  from  the  food. 
Labor  greatly  increases  the  exhalation  of  carbonic  acid,  but  does  not 
alfect  to  any  great  extent  the  excretion  of  urea. 

Formation  of  Urea. — The  chief  source  of  urea  is  from  the 
metabolism  of  the  muscles.  The  ingestion  of  a  large  amount  of  pro- 
teid food  stimulates  m.etabolism.  Muscles  contain  in  their  mass  over 
70  grams  of  creatin,  while  the  amount  of  creatin  excreted  is  only 
about  1  gram.  Urine  contains  about  30  grams  of  urea  and  muscles 
only  a  trace.  But  all  experiments  to  prove  an  actual  relation 
between  creatin  and  urea  have  been  failures. 

The  other  alloxuric  bodies — xanthin,  hypoxanthin,  and  uric  acid 
— are  also  to  be  regarded.  They  are  members  of  a  group  of  bodies 
having  as  their  base  of  formation  the  so-called  purin-ring  which  con- 
sists of  two  urea  radicles  linked  together  by  a  central  chain  of  car- 
bon atoms.     They  are  probably  split  up  in  part  into  urea. 

I  have  already  alluded  to  'arginin  as  a  source  of  urea.  All  the 
proteids  are  probably  split.  Tip  inter  bodies  which  form  ammonia. 
!N"ow,  when  we  give  by  the  m©uth  ammonia  salts  we  find  an  increase 
of  urea.  Further,  when  ammonia  salts  are  perfused  through  the 
liver  we  find  thut  urea  is  generated.  This  leads  us  to  believe  that 
the  liver  is  the"  c^^ief  manufactory  of  urea. 

In  Eck's  fistl^li^- when  an  artificial  communication  has  been 
made  between  the  portal  vein  and  the  inferior  vena  cava,  the  portal 
vein  may  be  tied  and  the  animal  lives.  After  the  Eck  fistula  the 
portal  blood  does  not  go  to  the  liver,  but  goes  to  the  vena  cava.  The 
hepatic  artery  is  still  sufficient  to  nourish  the  liver  after  Eck's  fistula. 

The  diversion  of  the  portal  blood  to  the  vena  cava  markedly 
diminishes  the  quantity  of  urea,  whilst  the  ammonium  salts  in  the 
urine  are  increased.  This  experiment  supports  the  view  that  urea 
is  formed  in  the  liver  from  ammonium  carbonate.  In  digestion  I 
have  alluded  to  arginin  being  converted  into  urea  in  the  liver  ))y 
the  ferment,  arginase. 

Yon  Nencki  has  shown  that  the  portal  vein  contains  three  to 
four  times  more  ammonia  salts  than  the  hepatic  vein  or  the  hepatic 
artery.  The  ammonia  comes  from  the  breaking  up  of  the  proteids 
l)y  trypsin  into  peptones,  which,  in  turn,  are  broken  up  by  erepsin 
into  the  amido-acids  and  ammonia. 

The  amido-acids  are  absorbed  as  such,  and  carried  by  the  blood 


398 


PHYSIOLOGY. 


to  the  tissues.  The  aniido-acids  not  used  in  tissue-building  have 
their  nitrogen  split  oil'  ra2)idl}'  without  loss  ol*  energy  and  eonverted. 
into  urea,  whilst  the  carbon  residue  is  retained  and  utilized  for  the 
production  of  energy  in  place  of  an  equivalent  energy  value  of  fat 
or  carbohydrate.  This  decomposition  takes  place  without  that  pre- 
liminary conversion  of  the  food  proteid  into  tissue,  contrary  to  the 
usual  prevalent  view  of  Pflueger.      (Abderhalden.) 

It  is  not  known  how  much  urea  is  formed  in  the  liver,  but  it  is 
not  far  from  half  the  amount  of  urea  excreted.     The  intracellular 


Fig.    169. — Urie-aeid    Crystals    with    Amorphous    Urates. 
(PuRDY,  after  Peyek.  ) 


ferments,  which  exist  in  nearly  all  the  tissues,  break  up  the  proteids 
of  lymph  into  annnonia,  which  is  also  converted  into  urea  by  the 
liver  and  by  other  tissues  at  present  not  known. 

During  sleep  the  amount  of  urea  excreted  remains  nearly  the- 
same  as  when  awake,  but  there  is  a  diminution  of  carbonic  acid 
exhaled  and  of  oxygen  inhaled.  These  results  are  due  to  muscular- 
quietude. 

Uric  Acid  (C^H^ISr^O.,). — This  constituent  is  scarce  in  human 
urine,  hardly  reaching  0.03  per  cent,  of  its  component  solids.  Next 
to  urea,  it  is  the  product  of  excretion  richest  in  nitrogen.     It  is  very 


SECRETION. 


399 


preponderant  and  jjerhaps  altogether  the  chief  excretion  in  birds, 
reptiles,  and  insects. 

Uric  acid,  or  lithic  acid,  is  colorless,  inodorous,  and  insipid;  it 
usually  crystallizes  in  whetstone  crystals,  which  have  for  a  funda- 
mental type  the  vertical  rhombic  prism.  It  is  insoluble  in  alcohol 
and  ether,  only  very  slightly  solnljle  in  water.  The  rhombic  crystals 
arc  characteristic  of  uric  acid. 

If  HCl  be  added  to  urine,  there  will  be  deposited  on  the  bottom 
of  the  vessel  after  several  h(nirs  a  deposit  resembling  Cayenne 
pepper.  Uric  acid  occurs  in  the  urine  as  acid  sodium  urate.  The 
HCl  decomposes  the  urates,  setting  free  the  acid,  which  does  not 
crystallize  at  once,  by  reason  of  the  presence  of  phosphates.     Accord- 


Uvic  Acid. 

Fig.  170. — Uric  Acid,  Effect  of  on  Intestinal  Peristalsis. 

ing  to  Liebig,  it  is  especially  by  the  phosphates  that  the  acid  is  dis- 
solved, under  the  form  of  urate. 

Uric  acid  is  dibasic,  so  that  there  are  two  classes  of  urates:  the 
normal  urates  and  the  acid  urates.  The  amorphous  urates  are  quad- 
riurates;   acid  urates  are  crystalline. 

Uric  acid  is  trioxy-purin.  The  purin  bases  are  hypoxanthin, 
xanthin,  adenin,  guanin,  and  uric  acid.  All  these  bodies  are  derived 
from  a  substance  called  purin. 

The  elimination  of  nitrogen  in  the  urine  can  be  augmented  by 
the  food.  Thus,  nuclein  (of  which  the  thymus  contains  a  large 
amount),  coffee,  cocoa,  and  meat  (veal  and  ham  especially),  cheesf, 
and  beer  are  rich  in  purins.  The  bodies  poor  in  purins  are  milk, 
potatoes,  white  bread,  rice,  eggs,  salads,  and  cabbage. 

FoRMATiox  OF  THE  Uric  Acid. — It  is  a  result  in  part  of  the 
breaking  up  of  the  nuclein  of  cells,  forming  xanthin,  which  Ijyxanthin- 
oxidase  is  changed  into  uric  acid. 


400 


PHYSIOLOGY. 


Biirian  holds  that  hypoxanthin  must  be  continually  produced 
in  the  muscles,  and  that  this  production  is  increased  by  muscular 
contraction.  Before  it  enters  the  blood  it  is  converted  by  xanthin- 
oxidase  into  uric  acid. 

Uric  acid  has  two  origins,  exogenous  and  endogenous.  The 
exogenous  origin  is  from  the  foods  containing  nuclein  or  purin  sul)- 
stances. 

The  endogenous  uric  acid  comes  from  the  metabolism  of  all 
cells,  but  especially  from  the  nuclein  of  the  leucocytes;  hence  it  is 
especially  increased  in  the  disease  where  there  is  an  excess  of  leuco- 
cytes, leucocythivmia. 


Fig.    171. — Urate  of   Soda   and   Crystals   of  Uric  Acid    {h) ,  Oxalate  of 
Lime    (o),  and   Cystin    (c).      X  350.      (Lenhartz.) 

Want  of  exercise  leads  to  an  increased  formation  of  uric  acid 
by  a  lessening  of  the  oxidation  of  the  tissues. 

In  gout  the  amount  excreted  in  the  urine  is  small,  while  it 
accumulates  in  the  blood  and  tissues. 

In  the  gouty  deposits  about  the  joints  the  so-called  "chalk 
stones"  contain  50  per  cent,  of  sodium  urate. 

Uric  acid  probably  circulates  in  the  blood  chiefly  as  a  mono- 
natrium  urate  or  in  combination  with  an  organic  acid. 

Uric  acid  and  lithic  acid  are  the  same.  Lateritious,  or  brick-dust, 
sediment  in  the  urine  is  composed  of  urates,  and  is  chiefly  sodium 
urate. 

The  average  daily  quantity  of  uric  acid  passed  in  the  urine  of 
man  might  be  calculated  at  about  7  grains.     When  the  quantity  is 


SECRETION.  401 

excessive^  it  very  frequently  liapjjeus  that  the  acid  is  deposited  iu 
the  form  of  urinary  calculi  and  gravel. 

To  increase  the  excretion  of  uric  acid,  the  best  means  is  to 
increase  the  secretion  of  urine  by  copious  draughts  of  water. 

MuEExiDE  Test. — Slowly  and  gently  heat  some  urine  and  nitric 
acid  in  a  porcelain  dish  to  the  point  of  dryness.  Decomposition 
takes  place,  the  color  changing  to  yellow,  and  N  and  CO,  are  given 
off.  After  allowing  the  yellow  stain  to  cool,  add  a  drop  of  dilute 
ammonia-water  to  it,  when  there  will  be  formed  with  the  uric  acid 
a  purplish-red  color  of  murexide.  On  the  addition  of  caustic  potash 
the  color  becomes  a  marked  blue. 

Hippuric  Acid  (C9H9XO3),  which,  in  the  herbivora,  is  the  prin- 
cipal representative  of  nitrogenized  regression,  is  scarce  in  human 
urine.  In  the  latter  it  appears  chiefly  after  the  use  of  some  fruits, 
such  as  apples,  plums,  and  grapes. 

Hippuric  acid  is  the  product  of  the  coupling  of  glycocin  with 
benzoic  acid.  It  may  also  be  formed  in  the  kidney  itself.  It  is 
monobasic,  very  slightly  soluble  in  cold  water  and  ether,  and  readily 
soluble  in  warm  water  and  alcohol.  It  crystallizes  in  vertical  rhom- 
bic prisms,  is  of  a  bitterish  flavor,  and  is  acid  in  reaction.  "When 
decomposed  by  heating  with  acids  and  alkalies,  or  when  transformed 
by  animal  ferments,  hippuric  acid  resolves  itself  into  its  components : 
benzoic  acid  and  glycocin.  Ingested  benzoic  acid  and  oil  of  bitter 
almonds  are  eliminated  with  the  urine  as  hippuric  acid. 

Some  of  the  hippuric  acid,  at  least,  is  the  product  of  the  activity 
of  (lie  secreting  cells  of  the  renal  tubules,  as  is  demonstrated  by  per- 
fusing. If  arterial  blood  containing  benzoic  acid  and  glycocin  be 
forced  through  the  blood-vessels  of  a  freshly  excised  kidney,  hip- 
puric acid  will  be  found  in  the  perfused  blood. 

The  food  of  herbivora  seems  to  be  an  important  factor  in  the 
manufacture  of  hippuric  acid.  AVhen  fed  upon  grain  without  the 
liusl',  hippuric  acid  is  absent.  Crystals  of  hippuric  acid  can  be 
readily  precipitated  from  the  fresh  urine  of  horses  and  cows. 

Lactic  Acid  is  a  constant  component  of  the  urine.  Its  quantity 
is  increased  when  it  abounds  in  the  blood  from  deficiency  of  oxida- 
tion, or  from  free  derivation  from  the  aliments,  or  from  gastric  fer- 
mentations. 

Oxalic  Acid  is  an  inconstant  component;  it  occurs  with  calcium 
in  the  crystalline  form  of  octahedrons.  The  crystals  are  insoluble 
in  acetic  acid,  but  are  readily  dissolved  by  hydrochloric  and  nitric 
acids.     The  "envclope"-shaped  crystals  are  very  characteristic. 

2G 


402  PHYSIOLOGY. 

Oxalic  acid  appears  to  be  derived  from  outside  the  economy, 
mainly  from  the  ingestion  of  vegetable  foods,  as  sorrel,  lemons,  rhu- 
barb, etc.     It  may  also  result  from  incomplete  oxidative  processes. 

Creatinin  occurs  in  the  urine  in  the  average  daily  amount  of  0.9 
gram.  Its  sources  are  believed  to  be:  (1)  the  creatin  of  muscles 
formed  by  the  subtraction  of  a  molecule  of  water  and  (2)  flesh  foods. 
If  creatin  be  fed  to  animals  it  appears  as  creatinin  in  the  urine; 
however,  if  it  be  injected  intravenously  it  appears  in  the  urine  as 
creatin;  so  that  it  is  very  improbable  that  the  kidneys  are  con- 
cerned in  its  manufacture. 

Xanthin,  hypoxanthin,  leucin  and  tyrosin,  and  traces  of  allan- 
toin  are  sometimes  formed  in  the  urine,  where  they  represent  nitro- 


Fig.   172. — Effect  of  Xanthin  on  Muscle  Curve,  Causing  an  Extra 
Contraction  during  the  Kelaxation.      (J.  F.  Ulman.  ) 

genized  bases  of  albuminoid  retrogression.  Glycuronic  and  homo- 
gentisinic  acids  are  found  in  the  urine  occasionally.  Children  of 
first  cousins  almost  invariably  have  in  their  urine  homogentisinic 
acid. 

Ammonia. — The  urine  always  contains  a  small  amount  of 
ammonia,  on  an  average  about  half  a  gramme. 

If  you  give  carbonate  of  ammonia  by  the  mouth  it  increases  the 
urea,  but  not  the  ammonia  in  the  urine.  If,  however,  a  more  stable 
ammonia  compound  is  given,  as  ammonium  chloride  or  benzoate, 
then  it  is  not  converted  into  urea,  but  is  excreted  as  chloride  or 
benzoate  of  ammonium.  The  previous  transformation  of  ammonia 
salts  into  a  carbonate  is  a  necessary  condition  for  the  ammonia  to 
be  converted  into  urea. 

The  body  defends  itself  normally  against  the  acids  generated 
within  it  by  proteid  metabolism,  by  the  ammonia  which  it  produces. 


SECRETION, 


403 


The  ammonium  salts  produced  are  inoffensive  and  are  eliminated  by 
the  kidneys. 

The  quantity  of  ammonia  in  the  urine  varies  with  the  food, 
being  greater  on  a  meat  diet  and  least  on  a  vegetable  diet. 

The  introduction  of  acids  into  the  organism  incapable  of  con- 
version into  carbonic  by  the  organic  oxidations  increases  the  amount 
of  ammonia  in  the  urine.  For  the  acid  introduced  combines  with 
a  part  of  the  ammonia  resulting  from  proteid  metabolism,  and,  not 
being  capable  of  transformation  into  carbonic,  is  excreted  by  the 
kidnevs  as  an  ammonium  salt. 


Fig.  173. — Leucin  in  Balls;  Tyrosiu  in  Sheaves.      (Peyer. ) 


In  this  way  we  see  the  means  by  which  the  body  resists  poison- 
ing by  the  acids  generated  within  it.  As  long  as  the  quantity  of 
ammonia  produced  suffices  to  neutralize  the  acids,  there  is  no 
trouble;  but  when  the  acids  are  in  excess,  as  in  the  acidoses  like 
diabetes,  then  there  is  a  fall  of  temperature,  difficult  breathing, 
drowsiness,  and  collapse.  The  introduction  of  alkaline  carbonates  or 
salts  of  organic  acids  which  are  convertible  into  carbonic  acid  dimin- 
ishes the  amount  of  ammonia  in  the  urine. 

In  the  body,  by  the  metabolism  of  the  proteids,  there  are  pro- 
duced incombustible  acids,  chiefly  sulphuric  and  phosphoric,  which 
combine  with  ammonia  to  be  excreted  as  such. 


404  THYSIOLOGY. 

In  serious  diabetes  there  is  an  abundant  production  of  organic 
acids  not  convertible  into_  carbonic  acid  in  the  body.  Such  are  the 
acetylacetic  and  beta-oxybutyric,  which  must  be  neutralized  by 
bases,  such  as  ammonia,  which  is  derived  from  the  meat  used  as  food 
and  from  the  proteid  metabolism  of  the  cells  of  the  body.  When 
this  ammonia  does  not  suffice  to  neutralize  the  acid,  then  the  sodium 
of  the  blood  is  called  upon;  the  blood  becomes  less  alkaline.  But 
the  sodium  of  the  blood  is  necessary  to  form  a  combination  with  the 
carbon  dioxide  for  it  to  make  its  exit  from  the  lungs. 

Coloring  Matters  of  the  Urine. — The  two  main  coloring  matters 
of  the  urine  are  urocliroine  and  urobilin.  Under  normal  physiological 
conditions,  urine  may  range  from  an  almost  colorless  or  pale  straw- 
yellow  through  intermediate  shades  until  reddish  brown  is  reached. 
The  commonest  condition  is  yellow.  Pale  urine  is  usually  of  low 
density;  high-colored,  of  high  density,  dependent  upon  the  con- 
stituents excreted  by  the  renal  epithelium.  In  addition  to  the  two 
main  coloring  matters  may  be  mentioned  uroerythrin  and  hcemato- 
porphyrin;  these  four  are  not  the  only  chromogenic  factors  in  the 
urine,  but  are  the  ones  that  are  best  known  to  us  to-day. 

Urobilin,  like  bile-pigment,  is  an  iron-free  derivative  of  haemo- 
globin. In  normal  urine  it  occurs  in  very  small  amounts  and  almost 
always  as  a  cliromogen;  only  rarely  is  it  found  free  in  physiological 
urine.  In  diseases  it  is  commonly  increased,  especially  in  the  highly 
colored  urines  of  feverish  patients.  It  gives  to  the  urine  a  peculiar 
reddish  color. 

Urobilin  is  identical  with  stercobilin.  The  theory  usually  ac- 
cepted concerning  its  mode  of  origin  is  that  bile-pigment  is  con- 
verted in  the  intestines  into  stercobilin;  while  the  major  portion  of 
the  stercobilin  leaves  the  body  combined  with  the  faeces,  neverthe- 
less some  is  reabsorbed  and  excreted  in  the  urine  as  urobilin.  Some 
observers  state  that  intestinal  micro-organisms  can  reduce  bilirubin 
to  urobilin. 

Ueocheosie  is  regarded  as  the  proper  pigment  of  the  urine,  giv- 
ing to  this  secretion  its  familiar  yellow  color.  When  removed  from 
this  medium  the  urine  loses  nearly  all  of  its  color.  It  is  separable 
into  yellow  scales.  Urochrome  may  decompose  to  produce  urome- 
lanin,  among  other  products.  The  last-named  constituent  gives  a 
blackish  tinge  to  the  urine. 

Ueoerythkin. — Aqueous  solutions  of  urochrome,  when  exposed 
to  the  air  and  so  oxidized,  turn  red  (uroerythrin).  This  coloring 
matter  is  familiarly  known  by  reason  of  its  association  with  the  acid 


SECKETION.  405 

sodium  urates,  which  it  colors  red  to  form  the  popularly  known 
"brickdust"  sediment.  jSTormally,  it  occurs  in  but  small  quantities, 
but  by  reason  of  its  strong  coloring  properties,  is  intimately  con- 
cerned in  the  coloring  of  the  urine. 

Three  properties  are  characteristic  of  uroerythrin:  (1)  its 
remarkable  affinity  for  uric-acid  compounds,  (2)  the  ease  with  which 
its  solutions  are  decolorized  by  light,  and  (3)  its  color-reactions  with 
caustic  alkalies  and  mineral  acids. 

H.i:matoporphyrin"  exists  in  but  very  small  amounts  in  the 
urine  normally;  pathologically  and  after  the  ingestion  of  certaiii 
drugs,  as  sulphonal,  it  may  be  greatly  increased. 

IxDiCAN",  OR  IxDOXYL. — This  is  another  pigment  which  colors 
the  urine  intensely  yellow.  It  is  an  indigo  substance  represented 
by  a  dense,  yellow-brown  acid,  nauseatingly  bitter  and  very  soluble 
in  water,  alcohol,  and  ether. 

Indican  is  derived  from  indol,  which  is  formed  in  the  intestines 
as  a  product  of  putrid  decomposition  of  the  pancreo-peptones.  It 
is  in  direct  relation  to  the  quantity  of  bacterial  putrefaction  of 
albumins.  Indican  is  really  a  conjugated  indoxyl  sulphate  of 
potassium. 

Test. — When  urine  is  mixed  with  an  equal  bulk  of  strong  HCl, 
indoxyl  is  liberated  from  the  sulphate.  A  solution  of  hypochlorite 
is  now  added,  drop  by  drop,  when  indigo-blue  will  be  formed  by 
oxidation  of  the  indoxyl.  Upon  the  addition  of  chloroform  the  blue 
matter  is  precipitated,  forming  a  layer  at  the  bottom  of  the  liquid. 

Pathological  Pigments. — Blood-pigmexts. — Blood  in  the  urine 
(hgematuria)  may  result  from  injury  or  disease  anywhere  along  the 
urinary  tract.  In  this  urine  the  red  blood-corj)uscles  are  found  in 
the  deposit.  An  idea  as  to  the  probable  source  of  the  haemorrhage 
may  be  gotten  by  careful  analysis.  Thus,  blood  from  the  kidney  is 
"usually  small  in  amount,  gives  urine  a  "smoky"  appearance,  and  is 
well  mixed.  Large  coagula  are  never  found  in  this  urine.  In 
haemorrhage  from  the  ureter  it  is  common  to  find  long,  wormlike 
coagula.  Bladder  haemorrhage  is  known  by  its  numerous  clots  and 
shriveled-up  leucocytes.  If  the  urine  be  alkaline,  crystals  of  triple 
phosphate  will  likely  be  found. 

In  Jicemoglohinuria,  the  pigments  exist  in  solution,  no  corpuscles 
being  found.  It  is  caused  by  the  excretion  of  haemoglobin  by  the 
kidneys  when  it  exists  as  a  free  body  in  the  blood-stream.  Free 
haemoglobin  is  due  to  active  hfemocytolysis,  which  is  produced  by  the 
injection  of  foreign  blood,  severe  burns,  etc. 


400  PHYSIOLOGY. 

BiLE-PiGJiEXTS  IN  THE  UiiixE. — It  is  usuallj  in  cases  of  icterus 
tliat  this  condition  exists  when  the  urine  becomes  of  a  decided  yel- 
low color.     The  pigment  usually  found  is  bilirubin. 

Bile-pigment  is  readily  detected  by  Gmelin's  reaction,  per- 
formed by  gently  pouring  the  urine  upon  the  surface  of  fuming 
nitric  acid,  when  a  green-colored  ring  appears. 

Carbolukia. — In  this  condition  the  urine  is  greenish  brown, 
becoming  darker  upon  exposure  to  the  air.  It  occurs  either  after 
poisoning  by  carbolic  acid  or  when  the  acid  has  been  administered 
as  a  drug. 

Drug-pigments. — After  the  administration  of  certain  drugs  the 
urine  is  sure  to  be  colored  differently  from  normal.  Those  which  do 
this  are  rhubarb,  ha^matoxylin,  santonin,  and  methylene  blue. 

The  Inorganic  Constituents. — These  are  derived  either  from  the 
aliments  with  which  they  are  introduced  into  the  body  or  they  are 
formed  in  the  organism  by  combination  with  bases  of  the  oxidized 
sulphur  and  alimentary  phosphorus.  They  are  eliminated  with  the 
urine  in  daily  amounts  from  16  to  24  grams. 

To  these  components  belong:  chlorine,  combined  chiefly  with 
sodium;  phosphoric  acid,  uniting  with  potassa,  soda,  calcium,  and 
magnesia  to  form  basic,  neutral,  and  acid  salts;  sulphuric  acid,  in 
part  combined  with  alkalies  and  in  part  united  to  indol  and  phenol 
in  the  form  of  aromatic  substances  (Baumann).  The  chlorides  and 
the  major  portion  of  the  phosphates  come  from  the  blood;  the 
sulphates  and  the  remainder  of  the  phosphates  from  the  activities 
of  metabolism. 

Chlorides  occur  in  the  form  of  sodic  chloride.  The  average 
quantity  excreted  is  180  grains  daily.  If  the  chlorides  be  in  excess 
in  the  food,  not  so  much  is  given  out  in  the  urine  as  has  been  intro- 
duced, since  part  passes  off  through  the  skin  and  rectum,  while 
another  part  accumulates  in  the  tissues.  Some  is  decomposed  to 
form  the  HCl  of  the  gastric  juice.  Sodium  chloride  is  absent  in 
early  stages  of  pneumonia. 

Phosphoric  Acid. — This  acid,  combined  to  form  the  alkaline 
(sodium  and  potassium)  and  earthy  (calcium  and  magnesium)  phos- 
phates, appears  in  the  urine  in  the  daily  quantity  of  about  2  grams. 
The  phosphoric  acid  of  the  urine  is  derived  principally  from  the 
alimentary  phosphates. 

Hence  there  is  an  increase  of  phosphates  after  a  meal  composed 
principally  of  meat,  after  muscular  and  nervous  labor.  There  is 
pathological  increase  in  diseases  of  the  brain  and  in  osteomalacia; 


SECRETION.  407 

there  is  diminution  in  pregnancy  by  reason  of  deposition  of  phos- 
phate within  the  fcutal  bones. 

The  Sulphuric  Acid  is  derived  from  the  liberation  and  oxida- 
tion of  tissue  sulphur.  Sulphuric  acid  occurs  in  the  urine  in  com- 
bination with  alkalies,  principally  sodium  and  potassium.  The  sul- 
phur introduced  into  the  system  medically  finds  egress  mainly  in  the 
fffices,  as  it  does  not  easily  pass  into  the  blood.  From  this  it  is 
inferred  that  the  sulphur  eliminated  is  derived  especially  from  the 
transformation  of  the  tissue-proteids.  It  runs  parallel  with  urea 
excretion.  The  daily  quantity  of  sulphates  excreted  is  3  grams. 
Proteid  contains  1  per  cent,  of  sulphur  and  IG  per  cent,  of  nitrogen. 
The  aromatic  or  conjugated  sulphates  form  one-tenth  of  the 
total  sulphates,  and  arise  from  bacterial  putrefaction  within  the 
intestinal  canal,  in  intestinal  obstruction,  typhoid  fever,  etc.  The 
chief  aromatic  (ethereal)  sulphates  are  phenol  sulphate  of  potassium 
and  indoxyl  sulphate  of  potassium. 

Cakboxic  Acid  in  a  state  of  combination  is  scarce  in  the  urine 
and  only  increases  there  after  the  use  of  alkaline  carbonates  and  of 
vegetable  acids,  which  latter  are  transformed  into  carbonic  acid  by 
oxidation. 

To  sum  up  in  an  approximate  average  the  very  variable  propor- 
tions of  the  principal,  normal  constituents  of  the  urine,  it  may  be 
said  that  with  a  mixed  diet  and  moderate  bodily  movement  there  are 
in  every  100  cubic  centimeters  of  daily  urine: — 

Water 96.00  grams. 

Solid  components   4.00       " 

Urea   2..30 

Uric  acid 0.03       " 

Sodium  chloride   0.80       " 

Pliosphoric  acid   0.15       " 

Sulpliuric  acid    0.20       " 

Earthy  phosphates    O.OS       " 

Ammonia   0.04       " 

Fermentation  of  Urine.— We  have  seen  that  the  reaction  of 
urine  is  generally  acid;  but  it  can  become  alkaline,  even  in  the 
physiological  state,  from  abundant  ingestion  of  alkalies,  or  of  salts 
with  organic  acid.  The  intensity  of  the  acid  or  alkaline  reaction  of 
urine  must  necessarily  vary,  not  only  with  the  proportion  of  the 
components  that  determine  it,  but  also  with  the  degree  of  dilution. 

The  acidity  of  the  urine  may,  however,  be  further  increased  by 
a  process  of  acid  fevmeniation  due  to  bacteria,  in  the  presence,  per- 
haps, of  vesical  mucus.     This  fermentation  may  take  place  outside 


408 


PHYSIOLOGY. 


of  the  bladder  as  well,  for  we  see  that  the  acidity  of  the  urine  con- 
tinues to  increase  from  the  time  of  emission. 

The  jDrocess  of  acid  fermentation  is  finally  accompanied  with 
development  of  a  mycelium  whose  spore  is  smaller  than  that  of  a 
torula.  It  appears  that  with  the  initiation  of  this  process  the  urine 
absorbs  oxygen  much  more  actively  (Pasteur). 

The  urine  is  also  subject  to  an  all'aUne  fermentation  due  to  an 
enzyme,  urease,  of  the  micrococcus  ureas.  It  generally  follows  the 
acid  fermentation,  but  may  occur  without  it,  in  the  bladder  as  well 
as  outside.  The  urine,  after  prolonged  exposure,  especially  in  a 
warm  atmosphere,  has  been  found  to  become  neutral  and  then  grad- 


Fig.    174. — Crystals   of   Ammonio-magnesium   Phosphate.      (After 

UlTZMANjST.  ) 

1,  Crystals  in  rosette  shape.     2,  Crystals  in  coffin-lid  shape. 

ually  alkaline.  This  fermentation  is  accompanied  with  decomposi- 
tion of  the  urea  into  ammonium  carbonate,  by  which  the  urine  is 
strongly  darkened  and  becomes  alkaline  and  of  a  strong,  putrid, 
ammonical  odor. 

In  disease  of  the  urinary  apparatus,  and  especially  in  vesical 
inflammation  and  catarrhs,  the  process  of  ammoniacal  fermentation 
is  already  advanced  in  the  urine  at  the  time  of  its  passage.  In  tliis 
case,  epithelial  mucus  and  purulent  elements  aid  in  making  it  turbid. 

On  the  basis  of  the  preponderance  of  one  group  of  combinations 
over  another,  they  are  divided  into  uric,  oxalic,  and  pliosplioric  sedi' 
ments. 


SECRETIOK 


409 


Ueic  Sediments. — These,  composed  of  uric  acid  and  the  alka- 
line and  earthy  urates,  increase  the  acidity  of  the  urine,  render  it 
muddy,  and  impart  to  it  a  brick-red  color,  which  is  made  more 
intense  by  exposure  to  the  air.  With  the  microscope  the  observer 
recognizes  in  the  sediment  the  characteristic  crystals  of  uric  acid. 

The  precipitation  of  urates  within  the  bladder  is  very  probably 
caused  by  concentration  from  the  absorption  of  water  from  the  urine. 
The  common  belief  that  holding  the  urine  predisposes  to  stone  is, 
therefore,  justified.  Another  and  more  frequent  cause  of  uric  sedi- 
ments in  the  bladder  is  the  acid  fermentation  which  may  occur  there 
from  the  presence  of  mucus,  as  in  vesical  catarrh.  These  are  strong 
predisposing  causes  to  uric  calculi. 


Fig.    175. — Ft-athery    Crystals    of    Triple    Phosphate.      X  350. 
(After  Tyson.) 


Oxalic  Sedimexts. — These  accompany  the  uric  sediments,  but 
there  may  be  a  predominance  of  oxalic  acid  combined  with  lime. 
This  sediment  is  recognized  by  its  crystals  of  calcium  oxalate,  the 
"envelope"  crystals.     They  are  insoluble  in  acetic  acid. 

They  are  chiefly  observed  in  deficient  respiration,  in  rickets,  in 
epileptiform  convulsions,  and  in  convalescence  from  serious  diseases. 
The  crystals  are  precipitated  by  neutralizing  the  acid  urine.  This 
explains  why  uric  calculi  are  often  mixed  with  oxalic  sediments. 
The  acid  urine,  with  its  uric  sediment,  readily  becomes  neutral  and 
alkaline  by  reason  of  purulent  catarrh  with,  therefore,  succeeding 
precipitation  of  the  oxalates. 


410  PHYSIOLOGY. 

Phosphoric  Sediments. — The  phosphoric  sediments  consist 
chiefly  of  crystallized  ammonio-magnesiuni  phosphate,  coffin-lid 
shaped  crystals,  and  of  calcium  phosphate. 

The  phosplioric  sediments  are  readily  distinguished  by  the 
alkaline  reaction  of  the  urine  and  by  their  insolubility  by  heat  (by 
which  the  urates  are  dissolved),  and  j^hosphoric  crystals  are  distin- 
guished from  oxalic  by  their  solubility  in  acetic  acid. 

The  phosphoric  sediments  acquire  importance  only  when  they 
are  formed  within  the  bladder,  either  by  purulent  products  or  by 
excessive  retention  of  urine,  as  in  paralysis. 

Sediments  in  Urine. — Acid  Urine. — Uric  Acid. — Ehombic 
prisms,  square  plates,  cubes,  ovoids  or  rosettes,  or  whetstone  or 
dumb-bell  crystals. 

Urates. — Brick-dust  or  lateritious  sediment,  irregular  amor- 
phous granules  of  a  brownish  or  pink  color.  They  are  composed  of 
sodium  acid  urate  and  potassium  acid  urate.  They  dissolve  when 
urine  is  heated. 

Calcic  Oxalate. — In  octahedral  crystals,  or  envelope  crystals,  or 
dumb-bell  crystals.  They  are  insoluble  in  acetic  acid  and  soluble  in 
hydrochloric  acid.  Cystin  appears  in  six-sided  tablets  having  an 
opalescent  luster  or  four-sided  square  prisms  lying  separately.     Eare. 

Leucin  appears  in  yellowish,  highly  refracting  spherules.     Eare. 

Tyrosin  appears  in  fine,  colorless  needles  arranged  in  sheaf-like 
collections  or  rosettes.     Eare. 

Xeutral  calciaim  phospliate  crystals  of  colorless  needles,  which 
group  themselves  with  points  in  a  common  center.     Eare. 

Sediments  in  Alkaline  Urine. — -1.  Amorphous.  Earthy  phos- 
phates; fine  granules  dissolving  in  acetic  acid  without  evolution  of 
carbon  dioxide. 

3.  Calcium  carl)onate  in  two  shapes:  (a)  fine  granules  solulj'e 
with  effervescence  in  dilute  acetic  acid;  (&)  dumb-bell  or  spheroidal 
masses,  dissolving  in  dilute  acetic  acid  with  evolution  of  carbon 
dioxide;   rare. 

3.  Acid  ammonium  urate.  Pigmented  spheres,  which  dissolve 
in  hydrochloric  acid  and  then  crystals  of  uric  acid  separate. 

4,  Ammonium-magnesium  phosphate.     Coffin-lid  crystals. 
Albumosuria. — In  cases  of  osteomalacia,  albumoses  are  found. 
Peptonuria. — In  the  stage  of  resolution  of  pneumonia  and  in 

cases  of  suppuration,  the  breaking  up  of  the  leucocytes  or  pus-cor- 
puscles produces  a  peptone,  or,  more  correctly,  a  deutero-proteose, 
which  appears  in  the  urine. 


SECRETIOX.  41 1 

Exceptional  or  Pathological  Components. — Besides  the  ordinary 
constituents  of  the  urine,  there  may  at  times  he  found  in  it  exeep- 
tional  ones  of  pathological  significance. 

Albumix. — Albumin,  and  more  properly  albumin  of  blood-serum, 
is  an  abnormal  component  of  the  urine  which  has  great  importance 
for  the  i^hysieian.  Its  presence  in  this  secretion  gives  the  clinical 
condition  commonly  termed  albuminuria.  Its  presence  is  due  to  a 
great  number  and  variety  of  causes,  a  few  of  which  are:  (1)  tem- 
porary or  lasting  increase  of  pressure  of  the  blood  within  the  renal 
system,  especially  hyperemia  from  cardiac  defect;  (2)  exanthemata 
(scarlatina),  and  febrile  diseases  in  general  (pneumonitis,  typhus, 
pygemia);  (3)  inflammation  and  degeneration  of  the  kidneys,  as  well 
as  disturbances  and  inflammation  of  the  brain  and  epilepsy;  (4)  any 
substance  which  acts  upon  the  vascular  system  of  the  kidneys,  such 
as  diuretics,  mercurials,  and  cantharides. 

The  recognition  of  albumin  in  the  urine  recjuires  care,  and,  above 
all,  it  is  necessary  to  remember  some  of  the  reactions  that  occur  in 
the  urine.  If  the  urine  be  acid,  the  albumin  accidentally  contained 
there  coagulates  at  temperatures  above  70°  C,  the  coagulation  first 
showing  as  an  opacity  upon  the  surface  of  the  liquid. 

Again,  if  the  urine  be  alkaline  and  then  subjected  to  heat,  there 
may  result  a  marked  opacity  without  the  presence  of  albumin,  the 
darkening  being  caused  by  precipitation  of  phosphates.  To  differ- 
entiate from  phosphates,  a  few  drops  of  acetic  acid  are  added,  which 
immediately  dissolve  them. 

Heller's  Nitric-acid  Test. — Albumin  is  also  recognized  by  means 
of  adding  one-fourth  of  the  proper  volume  of  IINO3.  The  reaction, 
a  ring  of  white  precipitate  occurring  at  the  junction  of  the  two 
liquids,  is  evident  when  there  is  much  albumin.  If,  instead,  the 
quantity  should  be  small  and  the  urine  concentrated,  nitrate  of  urea 
will  be  precipitated,  giving  an  erroneous  impression  to  the  observer. 
If  the  urine  be  diluted  one-fourth  with  water,  the  urea  precipitate 
disappears. 

A  method  of  measuring  the  quantity  of  albumin  present  in  iirine 
is  easily  accomplished  by  the  method  devised  by  Esbach.  The  essen- 
tial principle  is  precipitation  of  the  albumin  by  means  of  Esbach's 
reagent,  which  in  1000  cubic  centimeters  of  water  contains  10  grams 
of  picric  acid  and  20  grams  of  citric  acid.  This  is  performed  in  a 
test-tube  so  graduated  that  the  figures  represent  grams  of  dried 
albumin  in   a  lifer  of   urine.     It   is   essential  that  the  reaction   be 


412 


lMlVSI()L(HiV 


allowed  to  proceed  for  twenty-four  hours  Ix'fore  any  readings  arc 
taken. 

Proteoses  are  detected  l)y  the  precipitates  ])roduced  l)y  nitric  and 
salicyl-sulphonic  acids  clearing  u[)  on  heating  the  urine  and  return- 
ing on  cooling. 

SuGAK. — While  it  is  known  that  normal  urine  may  contain 
traces  of  sugar,  attention  is  recpiired  with  the  sugar  that  occurs  in 
excess,  especially  from  the  disease  known  as  diabetes  meilitus. 

In  the  first  place,  diabetic  urine  is  abnormal  in  amount,  even 
reaching  10  liters  a  day.     It  has  a  high  specific  gravity,  and  is  of  a 


Fig.   176. — Crystals  of  Phenylglucosazone.      (Purdy,   after  v.   Jakscii.  ) 


pale  and  greenish  yellow,  so  that  sugar  may  be  suspected  at  once; 
when  the  increased  density  is  due  to  urea  the  urine  is  intensely  red- 
dish. However,  it  must  be  remembered  that  the  nitrogenous  excreta 
are  also  increased. 

The  sugar  present  is  in  the  form  of  dextrose,  or  grape-sugar.  It 
is  increased  with  a  carbohydrate  diet  and  diminished  with  one  that 
is  nitrogenous.  Upon  standing,  there  are  developed  in  diabetic 
urine  torulce. 

FeMing's  Test. — Results  are  obtained  by  the  use  of  Fehling's 
solution.     This  is  an  alkaline  solution  of  copper  sulphate  to  which 


SECRETIOX.  413 

Eochelle  salt  has  been  added.  The  latter  holds  the  cupric  hydrate 
in  solution.  The  presence  of  sugar  is  denoted  by  the  reduction  on 
boiling  of  yellow  precipitate  of  cuprous  oxide. 

Phenylhydrazin  Test.- — -This  is,  perhaps,  the  most  trustworthy 
of  all  the  sugar  tests.  It  depends  upon  the  formation  of  a  very 
characteristic  body  from  phenylhydrazin  hydrochloride  and  sodium 
acetate:  phenylglucosazone.  The  resultant  body  is  found  as  yellow 
crystals,  for  the  most  part  arranged  in  rosettes  and  clusters.  They 
are  only  sparingly  soluble  in  water.  The  characteristic  crystals  are 
readily  detected  under  the  microscope. 

The  phenylhydrazin  test  takes  place  with  glucose,  lan'ulose,  and 
glycuronic  acid. 

Fermentation  Test  for  Sugar. — "With  an  Einhorn  saccharometer 
tube  introduce  a  definite  quantity  of  urine  and  a  piece  of  Fleisch- 
man's  yeast  about  the  size  of  a  pea;  then  stand  in  a  warm  place. 
Next  morning  read  off  the  percentage  of  glucose  on  the  instrument. 
The  fermentation  test  of  glucose  excludes  glycuronic  acid,  as  it  will 
not  ferment. 

Bile  and  Blood  in  the  urine  have  been  previously  discussed. 

Tube-casts. — Cylinders,  or  casts,  of  the  uriniferous  tubules  are 
of  prime  importance  to  the  physician  in  his  diagnosis  of  some  forms 
of  renal  disease.  Those  which  are  straight  may  be  said  to  be  casts 
of  the  collecting  tubes;  the  more  curved  and  twisted  ones  are  prob- 
ably from  the  convoluted  tubules.  Various  kinds  of  casts,  or  cylin- 
ders, are  distinguished. 

Theory  of  the  Urinary  Secretion. 

The  theory  of  the  urinary  secretion  is  summed  up  by  regarding 
the  water  (which  determines  the  quantity  of  the  urine)  and  its  salts 
as  a  product  of  filtration  from  the  renal  glomerules;  the  dissolved 
components  (as  urea,  uric  acid,  etc.)  as  products  of  the  special 
activity  of  the  elements  of  the  epithelium  of  the  contorted  tubules. 

That  the  passage  of  the  water  takes  place  chiefly  by  filtration 
is  shown  by  the  fact  that  the  quickness  of  this  passage  is  kept  m 
direct  relation  with  the  pressure  of  the  blood  in  the  renal  arteries, 
and  the  glomerules  in  particular,  from  whose  vessels  the  watery  ele- 
ment of  the  urine  is  chiefly  derived. 

Nevertheless,  hydrostatic  pressure  is  not  the  only  factor  at 
work  in  the  glomerules,  for  their  epithelium  exerts  both  a  positive 
and  negative  influence:    positive  in  that  some  of  the  =(alts  of  the 


414  PHYSIOLOGY. 

urine  are  here  secreted;  negative,  in  that  the  seruni-alljuniin  of  the 
blood  is  prevented  from  passing  through. 

In  support  of  the  part  that  blood-pressure  bears  to  secretion  it 
has  been  noted  that,  when  the  total  contents  of  the  vascular  appa- 
ratus are  increased  so  that  blood-pressure  also  increases,  there  fol- 
lows an  increased  secretion;  that  increased  action  of  the  heart 
increases  the  amount  of  urine;  and  that  variations  in  the  caliber  of 
the  renal  artery  give  proportionate  urinary  secretions. 

The  diuretics  made  use  of  by  the  physicians  owe  their  efficiency 
mainly  to  these  principles.  Digitalis  increases  the  quantity  of  urine 
by  raising  blood-pressure,  whereas  urea,  potassium  nitrate,  caffeine, 
etc.,  act  upon  the  rodded  epithelium  of  the  tubuli  contorti. 

It  must  not  be  forgotten  that  at  all  times  there  is  glomerular 
pressure  by  reason  of  the  vasa  effercntia  being  of  smaller  lumen  than 
that  of  the  afferentia. 


; Stirling,  after  Roy.)      (Fiom  IMills's  "Animal  Physiology,' 
copyright,  1889,  by  D.  Appleton  and  Company.) 

Kklnei)  curve.  Curve  of  the  volume  of  the  kidney.     T,  Time-curve;   intervals 
indicate  a  quarter  of  a  minute.     A,  Abscissa. 


Colheim  and  Roy,  in  their  experiments  with  the  oncometer,  have 
noted  that  the  curve  representing  the  volume  of  the  kidneys  runs 
parallel  with  the  curve  of  arterial  pressure;  it  has  smaller  oscilla- 
tions, both  respiratory  and  cardiac.  The  nervous  influences  acting 
upon  the  renal  secretion  are  vasomotor;  existence  of  the  so-called 
secretory  nerves  has  not  yet  been  definitely  demonstrated. 

Toxicity  of  the  Urine. — After  the  ablation  of  the  two  kidneys 
the  animal  dies  from  ura?mia;  that  is,  there  is  an  accumulation  of 
the  urinary  products  in  the  blood.  The  removal  of  one  kidney  is 
not  necessarily  fatal.  The  urine  of  daytime  is  more  toxic  than  that 
at  night;  it  is  especially  narcotic,  while  night  urine  is  more  con- 
vulsivant.  A  man  excretes  enough  poisonous  material  by  the  kid- 
neys in  two  days  to  cause  death.     When  there  is  an  excess  of  urea 


SECRETION.  415 

in  the  blood,  the  disease  is  termed  uraMiiia.  The  toxic  substance  is 
probably  not  urea,  but  some  other  organic  body.  The  usual  cause 
of  uiaimia  is  Bright *s  disease.  Uric  acid  in  excess  is  supposed  to  be 
the  cause  of  rheumatism  and  gout. 

Influence  of  the  Nerves  Upon  the  Secretion  of  Urine. — i\.s  has 
been  elsewhere  stated,  the  nerves  of  the  kidneys  are  derived  from 
the  renal  plexus  and  are  composed  of  both  meduUated  and  non- 
medullatcd  fibers  with  nerve-cells.  These  are  both  vasodilator  and 
vasoconstrictor  in  function.  As  yet,  no  true  secretory  nerves  are 
known,  so  that  it  is  by  the  influence  of  the  vasomotor  nerves  dis- 
tributed along  the  course  of  the  renal  vessels  that  variations  in  the 
amount  of  urine  secreted  occur.  Thus,  the  amount  of  urine  secreted 
depends  upon  the  pressure  of  the  blood  circulating  through  _  the 
capillaries. 

Frequent  and  small  urinations,  under  mental  apprehension, 
show  a  very  probable  nervous  intiuence  upon  the  excretion  of  the 
urine.  Polyuria  and  the  peculiar  aspect  of  the  urines  of  hysteria 
are  also  known;  whether  these  peculiarities  are  dependent  upon 
direct  nervous  influence  upon  the  secretion  is  not  known.  Ludwig 
believes  that  the  cause  lies  in  the  increased  pressure  in  the  renal 
arteries  from  spastic  contraction  of  other  vascular  regions. 

Injur}'  by  puncture  of  the  vasomotor  center  in  the  floor  of  the 
fourth  ventricle  likewise  is  followed  by  polyuria.  accomjDanied  by 
ha^naturia  and  albuminuria.  By  this  experiment  it  is  demonstrated 
that  variations  in  urinary  secretion  are,  for  the  most  part,  very  inti- 
mately concerned  with  vasomotor  innervation. 

If,  while  the  renal  vasomotors  are  paralyzed,  the  majority  of  the 
vasomotor  nerves  of  the  entire  body  be  also  paralyzed  (as  by  section 
of  the  medulla),  there  follows  a  general  dilatation  of  the  arterioles 
and  capillaries  of  the  body.  This  causes  such  a  decided  fall  in  the 
l)lood-pressure  that  the  amount  of  urine  secreted  is  much  diminished 
or  entirely  absent. 

However,  secretion  is  not  suspended  by  removal  of  the  brain, 
nor  destruction  of  the  spinal  cord  below  the  cervical  portion,  pro- 
vided that  the  medulla  is  intact  and  with  it  the  respiration  and  cir- 
culation.    (Krimer.) 

Urinary  Excretory  Apparatus. — After  the  urine  has  been  se- 
creted by  the  kidneys,  it  must  needs  be  carried  away  from  the  body, 
so  that  the  economy  may  not  suffer  from  resorption  of  contained 
toxic  principles,  as  well  as  not  to  interfere  with  the  renal  action  by 


416  PHYSIOLOGY. 

tMlualizing  pressure  ivilJiiii  lliat  organ  from  (lainiiiiiig  l)ack  oi'  the 
urine. 

The  excretory  apparatii.s  eoni])rises  the  urclers,  bladder,  and 
iireihra. 

The  Uketers  are  two  cylindrical  membranous  tuLes  of  the 
diameter  of  a  goose-quill  and  al)out  fifteen  inches  long.  They  extend 
from  the  pelvis  of  the  kidney  to  the  hladder,  to  which  viscus  runs 
the  urine  from  the  kidneys.  The  general  coui'se  of  each  ureter  is 
downward  and  inward  toward  the  median  line,  to  empty  into  the 
base  of  the  bladder  by  a  constricted,  slitlike  orifice.  The  ureter  runs 
for  nearly  an  inch  between  the  muscular  and  mucous  coats  of  the 
bhadder  before  it  makes  its  exit  upon  the  inner  wall  of  the  organ. 

Structure. — The  ureter  is  composed  of  three  coats,  or  layers: 
serous,  or  adveiititia;  muscular;   and  mucous. 

The  adventitia  is  continuous  with  the  capsule  of  the  kidney  at 
one  end  and  with  the  fibrous  layer  of  the  bladder  at  the  other.  In 
it  are  found  its  larger  vessels  and  nerves. 

The  muscular  coat  comprises  the  two  usually  distinct  muscular 
layers:    an  external  longitudinal;   an  internal,  circular  one. 

The  mucous  coat,  continuous  with  that  of  the  bladder,  lines  the 
ureter.     It  is  composed  of  stratified  epithelial  cells. 

Movement  of  the  Urine. — The  urine  flows  into  the  tubules  by  the 
vis-a-tergo  pressure  of  the  blood  in  the  afferent  capillaries.  This 
averages  from  120  to  140  millimeters  of  mercury.  This  force,  which 
is  capable  of  making  the  urine  flow  through  the  tubules,  is  incapable 
of  forcing  the  urine  through  the  ureters.  By  reason  of  the  ureters 
taking  a  diagonal  course  through  the  vesical  wall,  the  weight  of  the 
urine  alread}^  in  the  bladder  must  exert  a  certain  amount  of  pressure 
upon  this  portion  of  each  ureter.  To  overcome  this  some  auxiliary 
force  must  be  called  into  action,  which  is  the  peristaltic  contraction 
of  the  iireters.  This  movement  begins  at  the  kidneys  and  is  trans- 
mitted (with  a  speed  of  from  20  to  30  millimeters  per  second)  down- 
ward into  the  bladder.  With  the  completion  of  each  peristaltic 
movement  there  exudes  into  the  bladder  a  drop  of  urine.  The  move- 
ments of  the  two  ureters  are  not  synchronous;  they  are  reflex,  being 
caused  by  the  presence  of  urine  in  the  lumen  of  the  ureter. 

In  a  case  of  Dr.  W.  Easterly  Ashton's,  where  the  ureters  opened 
on  the  abdominal  surface,  I  counted  an  emission  of  urine  by  the 
ureter  every  twenty-four  seconds. 


SECRETION. 


417 


The  greater  the  distension  of  tlie  lumen  of  the  ureter,  tlie  more 
rapid  will  the  number  of  peristaltic  movements  become. 

Experimentally,  peristaltic  movements  may  be  aroused  by  elec- 
trical or  mechanical  excitation;  movements  always  begin  at  the  point 
excited  and  proceed  toward  both  ends. 

The  Urinaey  Bladder. — The  bladder  is  a  niusculo-membran- 
ous  pouch  which  serves  as  a  temporary  reservoir  for  the  urine.     It 


Sup' 


^nes.  ganglion, 


•^f  nzesejiierii- 
ffanglupnr 


7teri/es. ''~' 


,2iecf7i/n 


Mcdder. 


"^'SympalhetiQ  chttzth 


yLumbarnerves. 


•■ULmScKral 
nervts. 


tectum. 


Fig.    178. — Diagram   of    Nerve-supply   to    Bladder. 
(Nawrocki,  Skabitchewsky,  and  Starling.) 

lies  behind  the  pubis  and  within  the  pelvic  cavity  while  the  viscus  is 
empty,  but  when  distended  it  protrudes  into  the  hypogastric  region, 
in  extreme  cases  even  up  to  the  umbilicus. 

In  the  cat,  two  days  after  section  of  the  spinal  cord  above  the 
vesico-spinal  center,  I  found  that  a  pressure  of  140  millimeters  of 
water  was  required  to  overcome  the  tonus  of  the  sphincter  when  a 
cannula  was  bound  in  the  urethra. 

27 


418  PHYSIOLOGY. 

Micturition. — When  the  act  of  micturition  takes  place  the  spinal 
detrusor  center  is  excited  into  activity  by  the  pressure  of  the  urine; 
the  sphincter  reflex  center  is  also  independently  excited  by  the  pres- 
sure of  the  urine,  and  opens  to  expel  the  secretion.  The  spinal 
detrusor  and  spinal  sphincter  are  under  the  control  of  a  cerebral 
detrusor  center  which  I  have  shown  to  be  seated  in  the  locus  niger, 
and  which  is  set  in  activity  by  the  cerebral  hemisphere  in  voluntary 
micturition.  The  detrusor  center  sends  its  impulses  down  the  lateral 
columns  of  the  spinal  cord  to  the  vesico-spinal  center. 

Voluntary  micturition  is  materially  aided  by  the  action  of  the 
abdominal  and  respiratory  muscles. 


CHAPTER  IX. 

METABOLISM. 

The  food  that  has  been  properly  digested  within  the  stomach 
and  intestines  is  absorbed  by  the  chyle  vessels  and  the  small  capil- 
laries by  whose  union  is  formed  the  portal  vein.  When  once  in  the 
blood-stream,  it  circulates  with  the  blood-current,  which  carries  it 
to  all  of  the  various  organs  and  tissues  of  the  body.  The  absorbed 
nutritive  products  are  held  in  solution  within  the  plasma  of  the 
blood. 

In  order  to  nourish  the  structures  outside  of  the  vessel-walls, 
the  plasma  with  its  contained  nourishment  is  constantly  being  dial- 
yzed  through  the  capillary  walls  into  the  spaces  between  the  living 
cells.  By  this  provision  each  cell  is  bathed  in  a  plentiful  supply  of 
plasma,  from  which  medium  it  absorbs  its  nutriment. 

The  various  stages  of  the  nutritive  process — viz. :  the  transuda- 
tion of  the  nutritive  plasma  from  the  blood,  the  assimilation  of  parts 
of  this  by  the  tissues  under  repair,  the  absorption  of  the  other  por- 
tion by  the  lymphatics,  and,  last,  the  reabsorption  of  the  final  resi- 
due, together  with  that  of  the  waste-products  of  the  tissues  by  the 
veins — are  performed  simultaneously  and  continuously  in  the  living 
body.  With  the  entire  organism  in  a  healthy  condition  there  is  a 
perfect  balance  of  action. 

Action  and  use  are  always  followed  by  a  corresponding  amount 
of  waste.  The  machinist  must  be  making  repairs  to  the  locomotive 
or  other  machine  that  is  in  use.  So  the  tissues  of  the  body  are  con- 
tinually being  destroyed,  to  pass  away  as  effete  matters  due  to  exer- 
cise and  action  of  the  various  organs  and  parts  of  the  economy. 
Thus,  the  simple  movement  of  the  finger,  our  very  thoughts  and  rea- 
sonings, are  productive  of  waste  in  the  tissues  concerned. 

It  is  due  to  the  repair  by  the  machinist  that  the  machine  is  kept 
in  normal  running  order;  likewise  it  is  due  to  the  proper  absorption, 
assimilation,  and  elimination  of  foodstuffs  taken  into  our  own  econ- 
omies that  the  body  owes  its  normal  function  and  health. 

The  digested  products,  having  arrived  at  their  destination  in  the 
organs  and  tissues,  undergo  two  kinds  of  chemical  processes  in  the 
presence  of  oxygen  and  under  the  peculiar  activity  of  the  cells.  The 
one  i&  anaholism,  or  upbuilding;  the  other  catabolism,  or  destruction. 

(419) 


420  PHYSIOLOGY. 

These  two  processes  arc  diametrically  opposite  to  one  another,  so 
that  by  virtue  of  the  one  the  organism  increases  in  bulk ;  by  virtue 
of  the  other  its  bulk  is  diminished. 

By  reason  of  the  anabolic  processes  the  nonliving  materials  of 
the  food  are  converted  into  the  complex  molecules  of  the  living 
tissues,  where  they  are  stored  up  to  form  a  store  of  potential  energy. 
At  any  time  the  organism  is  capable  of  transforming  this  potential 
energy  into  hinetic,  which  is  usually  most  conspicuous  to  the  observer 
as  heat  and  motion. 

By  the  transformation  the  complex  tissues  are  broken  down  into 
excretory  products  whose  structure  is  simple.  The  waste-materials 
leave  the  cells  to  be  carried  by  the  lymphatics  into  the  blood-stream, 
ultimately  to  reach  the  exterior  of  the  body  as  excreta  or  as  compo- 
nents of  some  secretions. 

The  two  processes,  auabolism  and  catabolism,  taken  conjointly 
constitute  what  is  known  as  metabolism:   an  exchange  of  material. 

Normal  metabolism  thus  re(|uires  the  ingestion  of  a  suitable 
quality  and  quantity  of  food,  wiiich  must  be  absorbed,  assimilated, 
and  stored  within  the  tissues.  In  the  latter  place  there  must  occur 
the  necessary  transformation  of  the  food  in  its  now  complex  form 
into  simpler  products  of  effete  nature,  evolving,  at  the  same  time, 
those  functions  and  activities  which  are  common  to  the  organism. 
In  short,  all  of  the  physiological  phenomena  demonstrable  in  the 
economy  are  the  result,  either  directly  or  indirectly,  of  anabolic  or 
catabolic  changes. 

Equilibrium  of  Metabolism. — By  this  term  is  meant  that,  ordi- 
narily, just  as  much  foodstuffs  are  stored  up  within  the  tissues  as 
effete  matters  and  excretions  find  egress  from  the  economy.  For 
the  organism  to  remain  normal  there  must  exist  a  balance  between 
income  and  output.  So  long  as  this  condition  lasts  the  body  main- 
tains its  bulk,  while  at  the  same  time  it  is  capable  of  performing  its 
necessary  functions.  Should  this  equilibrium  be  disturbed,  there 
will  occur  marked  changes  dependent  upon  whether  anabolic  or  cata- 
bolic processes  are  in  the  ascendancy. 

Anabolic  Processes  become  visible  during  (1)  the  growth  of  the 
body  in  infancy  and  adolescence,  and  (2)  during  convalescence  from 
a  serious  and  debilitating  disease. 

Catabolic  Processes  become  evident  during  old  age  and  in  the 
course  of  malignant  diseases.  Catabolism  is  the  destruction  of  tis- 
sue, from  which  process  result  the  numerous  manifestations  of  life. 

Catabolism  is  carried  on  by  means  of  different  chemical  forces : — 


METABOLISM.  421 

1.  Duplication:  that  is,  the  decomposition  of  an  organic  sub- 
stance into  two  or  more  products  whose  sum  represents  exactly  the 

.primitive  substance. 

2.  Dehydration. — This  is  a  particuhir  form  of  duplication  in 
which  one  of  the  products  is  water. 

3.  Oxidation. — This  is  the  most  important  part  of  the  chem- 
ical processes.  By  this  means  the  decomposition  is  accomplished 
with  fixation  of  oxygen,  such  as  the  decomposition  of  albumin, 
sugars,  and  fats. 

4.  Synthesis. — This  is  the  combination  of  two  or  more  sub- 
stances whereby  result  a  third,  new  substance.  Syntheses  are  char- 
acteristic of  anabolism,  but  yet  they  do  occur  in  cataholism.  Thus, 
with  the  disintegration  of  the  tissue-elements  into  benozic  acid  and 
glycocoll,  there  follows  hippuric  acid;  urea  is  formed  from  carbonic 
acid  and  ammonia. 

THE  AIM  OF  ALIMENTATION. 

Alimentation  has  for  its  end  (1)  to  furnish  materials  for  catah- 
olism, and  (2)  to  furnish  suitable  products  for  anabolism.  That 
is,  to  replace  and  rejuvenate  the  organized  substances  which  are 
destroyed  in  the  former  process. 

To  know  what  are  the  foods  which  the  body  needs,  it  becomes 
necessary  to  study  the  substances  which  undergo  anabolism  and 
cataholism.  It  is  these  substances  which  must  enter  into  our  daily 
nourishment.  These  two  processes  ensue  in  all  of  the  substances, 
without  any  exception,  which  compose  the  organism.  Hence,  all  the 
principles  of  which  the  economy  is  composed  are  indispensable  in 
food:    water,  proteids,  fat,  carbohydrates,  and  salts. 

Foods. — Each  one  of  these  principles  taken  in  an  isolated  man- 
ner is  not  a  complete  food,  since  it  is  not  able  to  replace  its  neigh- 
bor. Thus,  water  is  as  necessary  a  food  as  is  proteid,  but  yet  neither 
is  a  complete  food. 

A  food  is  any  product  which  is  capable  of  being  transformed  into 
a  proximate  principle  of  the  organism,  or  capable  of  at  least  dimin- 
ishing or  preventing  the  destruction  of  this  principle.  Hence,  a 
complete  food  is  the  sum  of  the  food-products  capable  of  preserving 
or  augmenting  the  sum  of  the  proximate  principles  of  which  the 
organism  is  composed. 

The  fundamental  principles  which  enter  into  the  chemical  com- 
position  of  the  human  body — water,  proteids,  fats,  carbohydrates, 


422  PHYSIOLOGY. 

and  salts — are  in  themselves  composed  of  simple  elements:  0,  H, 
C,  S,  N,  r,  CI,  K,  Na,  Ca,  Mg,  Fe,  silicon,  and  fluorin. 

Will  these  simple  elements,  upon  ingestion,  become  converted 
into  compk'x  principles  and  so  constitute  foods? 

They  will  in  the  case  of  the  plant,  for  it  is  able  to  form  a  com- 
plex frame  by  the  aid  of  simple  elements.  The  plant  is  a  synthetic 
laboratory  of  chemistry.  But  this  is  not  true  of  the  animal  organiza- 
tion. The  latter  is  incapable  of  anabolism  and  life  except  by  the 
aid  of  complex  food-combinations  such  as  have  been  formed  by  the 
plant.  Contrary  to  the  plant,  the  animal  is  a  laboratory  of  analytical 
cheinistry.  The  animal  can  only  form  by  synthesis  combinations  of 
a  low  degree,  as  Avater,  benzoic  acid,  and  ammonia,  which  cannot  be 
Iniilt  up  in  the  animal.  But  the  plant  can  take  H,  0,  COg,  and  N, 
and  from  them  make  complex  and  elevated  combinations. 

BALANCE  OF  NUTRITIVE  EXCHANGE. 

To  ascertain  the  balance  of  nutritive  exchange,  a  comparison  is 
made  between  the  ingesta  and  egesta:  between  the  gains  and  losses. 
The  ingesta  consist  of  food  and  oxygen ;  the  egesta  of  various  excreta 
and  of  the  carbon  dioxide  and  water  lost  by  the  lungs  and  skin. 
When  the  ingesta  equal  the  egesta  and  the  organism  neither  gains 
nor  loses  weight,  there  is  a  complete  nutritive  equilibrium. 

A  balance  of  water  is  made  by  giving,  upon  the  one  side,  the 
quantity  of  water  ingested  by  the  foods  and  drinks;  upon  the  other, 
the  quantity  of  water  eliminated  by  the  stools,  urine,  skin,  and  lungs. 
As  the  hydrogen  contained  in  the  food  is  oxidized  and  transformed 
into  water,  it  is  evident  that  in  a  state  of  equilibrium  the  quantity 
of  w^ater  eliminated  will  be  much  greater  than  that  ingested.  By 
comparing  the  water  ingested  with  the  water  egested,  it  is  found  how 
much  oxygen  serves  to  burn  the  hydrogen. 

Definite  enough  information  is  obtained  regarding  the  balance 
of  metabolism  if  the  nitrogen  and  carbon  only  are  determined  in  the 
ingesta  and  egesta. 

The  balance  of  proteid  is  made  by  a  comparison  of  the  nitrogen 
ingested  with  that  egested,  for  the  amount  of  nitrogen  permits  us  to 
know  the  quantity  of  proteid,  since  100  parts  of  proteid  contain  16 
parts  of  nitrogen.     The  nitrogen  eliminated  is  found  in  the  urine. 

Nearly  all  of  the  proteid  that  is  destroyed  is  found  in  the  form 
of  urea,  uric  acid,  creatinin,  and  hippuric  acid  in  the  urine.  There 
is  also  found  in  the  stools  proteid  which  has  not  been  digested  or 
absorbed  along  the  digestive  tract.     A  part  of  the  nitrogen  is  elimi- 


METABOLISM.  423 

nated  by  the  desquamation  of  hairs,  nails,  and  epidermis.  But  it 
usually  suffices  to  determine  the  amount  of  nitrogen  in  the  stools 
and  urine. 

If,  in  making  up  the  balance,  it  be  found  that  the  ingesta  have 
more  than  equaled  the  egesta,  it  is  concluded  that  there  has  been  an 
anahuUsm  of  nitrogen.  On  the  other  hand,  should  the  egesta  con- 
tain more  nitrogen  than  the  ingesta,  then  there  has  been  a  catahoUsm 
of  proteid.  Should  the  income  and  output  be  equal,  it  is  concluded 
that  there  is  a  state  of  nitrogenous  equilibrium. 

The  carlon  contained  in  the  foods  and  organized  tissues,  and 
which  is  destroyed  by  catabolic  phenomena,  is  eliminated  by  the  skiu 
and  lungs  under  the  form  of  CO,,  by  the  urine  and  stools  under  the 
form  of  carbonated  organic  compounds.  From  the  comparisons  of 
the  ingesta  and  egesta  it  is  ascertained  whether  there  be  carbon 
anabolism,  catabolism,  or  equilibrium. 

The  proteids,  fats,  and  carbohydrates  all  contain  carbon;  so  that 
if  there  be  a  gain  or  loss  of  carbon  it  may  be  from  the  proteids,  fats, 
and  carbohydrates.  To  arrive  at  some  solution,  it  becomes  necessary 
to  calculate  the  quantity  of  nitrogen  eliminated.  Every  hundred 
parts  of  proteid  contain  53.6  parts  of  carbon  and  16  parts  of  nitro- 
gen. If  it  be  known  how  much  proteid  has  been  destroyed,  nothing 
is  easier  than  to  calculate  the  quantity  of  carbon  which  belongs  to 
it.  The  remaining  carbon  that  is  eliminated  must  belong  to  the  fats 
and  carbohydrates. 

All  of  the  carbohydrates  ingested,  except  those  stored  up  as 
glycogen,  are  burned  up  in  the  metabolism  of  the  tissues  and  their 
carbon  found  in  the  excreta.  Hence,  by  calculating  the  quantity  of 
carbon  which  is  found  in  the  ingested  carbohydrates,  one  finds  what 
quantity  of  carbon  eliminated  belongs  to  the  decomposition  of  the 
carbohydrates.  If  there  be  an  excess  of  carbon  it  must  come  from 
the  fats,  since  the  latter  contain,  as  a  mean,  76.5  per  cent,  of  carbon. 
By  multiplying  the  surplus  of  carbon  by  1.3,  there  is  found  the  quan- 
tity of  fat  which  is  gained  or  lost. 

METABOLISM. 

Catabolism  varies  according  to  the  age  and  weight  of  the  ani- 
mal; the  younger  and  lighter  the  animal,  the  greater  is  the  relative 
destruction  of  proteid. 

Peptones  and  albumoses  have  about  the  same  caloric  and  nutri- 
tive value  as  the  proteids.     Most  of,  if  not  all,  the  proteids  contain 


424  PHYSIOLOGY. 

sulphur,  and  the  nucleo-proteids  contain  phosphorus.  An  increase 
of  sulphates  in  the  urine  indicates  proteid  metabolism. 

As  agents  to  spare  proteid  metabolism,  gelatin  ranks  first,  then 
carbohydrates,  and  next  fats.  Gelatin,  however,  cannot  be  built  up 
into  tissue,  nor  even  into  gelatin. 

The  serum-albumin  and  the  serum-globulin  are  the  chief  pro- 
teids  of  the  blood  which  are  transformed  in  metabolism. 

The  proteids  of  the  body  arise  from  the  food-proteids,  as  fats 
and  carbohydrates  cannot  form  proteids,  but  only  save  them  from 
metabolism. 

By  nitrogen  equilibrium  we  mean  the  condition  of  man  when 
the  nitrogen  of  the  egesta  is  equal  to  the  nitrogen  of  the  ingesta, 
and  this  is  the  normal  state  of  man  when  properly  nourished.  If 
the  nitrogen  of  the  ingesta  is  increased,  or  even  in  excess,  it  is  not 
deposited  in  the  tissues,  but  after  a  short  time  is  excreted,  the  man 
eating  more  and  excreting  more. 

By  carbon  equilibrium  is  meant  a  condition  in  man  where  the 
total  carbon  of  the  excreta  is  equal  to  the  carbon  taken  in  in  ingesta. 

Nitrogen  Equilibrium. 

The  quantity  of  proteid  food  to  preserve  nitrogenous  equili- 
brium varies  with  the  state  of  the  body ;  a  thin  man  needs  less  than 
a  muscular  and  well-nourished  one. 

A  body  can  be  maintained  by  proteid  food  alone  in  a  state  of 
nitrogen  equilibrium.  If,  however,  you  add  nonproteid  foods,  it  is 
seen  that  the  amount  of  proteid  necessary  to  nitrogen  equilibrium 
can  be  lessened;  hence  the  nonproteid  foods  are  sparers  of  proteid. 
Hence  you  decrease  the  proteid  food  and  increase  the  nonproteid 
food,  yet  the  body  does  not  lose  more  proteid  than  before,  and  nitro- 
gen equilibrium  continues  as  before.  The  proteids  develop  energy 
by  oxidation,  especially  that  form  manifested  in  the  shape  of  heat, 
and  also  reconstitute  the  protoplasm.  But  the  nonproteid  foods  can 
also  develop  heat  and  work,  and  thus  can  substitute  for  the  proteid 
foods  in  part. 

Hence  an  animal  may  be  kept  in  nitrogen  equilibrium  on  a  much 
smaller  amount  of  proteids,  provided  fats  or  carbohydrates  are  eaten. 

When  a  fat  animal  takes  proteid  in  large  amounts,  then  the 
destruction  of  "fat  is  increased ;  and  if  there  is  hardly  any  fat  in  the 
food,  the  fat  stored  up  in  the  animal  will  lessen. 


METABOLISM.  425 

Proteid  Metabolism. 

Normally,  the  body,  when  it  takes  in  nitrogen,  does  not  store 
it,  but  gives  it  off  in  the  shape  of  urea,  uric  acid,  and  creatinine 
hence  the  consumption  of  proteid  is  determined  by  the  supply. 
Another  peculiarity  of  nitrogenous  metabolism  is  that  muscle  work 
does  not  interfere  with  it;  that  is,  the  amount  of  nitrogen  in  the 
urea  excreted  is  the  same  whether  the  body  is  working  or  at  rest. 

Pliilger,  with  his  dog  fed  upon  flesh  a  long  time  and  working 
hard,  excreted  somewhat  more  nitrogen,  so  that  some  proteid  is  used 
in  work.  But  when  fats  and  carbohydrates  are  abundant  they  are 
the  main  source  of  energy  in  muscular  work.  One  hundred  to  one 
hundred  and  twenty  grams  of  proteid  should  be  allowed  daily  per 
adult. 

Man  can  live  only  when  the  chemical  elements  are  arranged  m 
a  certain  manner  with  others  in  the  form  of  foods,  for  the  propor- 
tion of  carbon  to  nitrogen  in  foods  is  not  that  required  in  a  diet. 
If  sufficient  proteid  was  used  to  supply  carbon,  the  diet  would  con- 
tain four  times  more  nitrogen  than  the  body  needs.  If  he  received 
enough  proteid  to  furnish  the  nitrogen  required,  then  he  would  be 
deficient  in  carbon.  Hence  it  is  plain  that  man's  diet  should  be 
made  up  of  proteids,  fats,  carbohydrates,  water,  and  salts. 

Each  gram  of  nitrogen  corresponds  to  6.25  grams  of  proteid; 
and  since  meat  contains  on  an  average  34  per  cent,  of  nitrogen,  each 
gram  of  the  latter  will  represent  30  grams  of  muscle. 

EFFECTS  OF  STARVATION  UPON  THE  DESTRUCTION  OF 

PROTEID. 

The  influence  of  starvation  upon  the  catabolism  of  the  proteids 
has  been  studied  upon  animals  and  in  man. 

The  nitrogen  in  the  urine  falls  rapidly  at  the  beginning  of  the 
experiment.  Then  it  reaches  a  minimal  amount,  which  continues 
the  same  for  several  days.  When  the  fat  of  the  animal  has  been 
used  up,  the  nitrogen  excreted  rises,  and  rapidly  falls  with  the 
approach  of  deatli.  About  the  same  changes  occur  in  the  amount 
of  sulpliates  and  phosphates. 

The  intake  of  oxygen  and  out-take  of  carbonic  acid  fall,  but  not 
so  rapidly  as  the  body  decreases  in  weight.  In  the  last  stages  both 
are  minimal.  The  bile  and  fasces  decrease.  The  loss  of  weight  is 
greatest  in  the  muscles,  fat,  liver,  and  blood;  the  heart  and  brain 
lose  but  little  weight. 

In  the  fast  of  Succi,  Luciani  found  that  a  nitrogen  excretion  of 


Day  ok  Fast. 

Pkoteii)  in  < 

iUAMS. 

1 

104 

10 

51 

20 

33 

29 

31 

426  ruYSiOLOGY. 

1G.23  grams  decreased  on  the  first  day  of  fasting  to  13.8,  on  the 
seventeenth  day  to  7.8  grams,  on  the  twenty-second  day  to  4.75 
grams,  on  the  twenty-eighth  day  to  T).!)  grams. 

Paton  gives  tlie  foik)wing  tal)le  to  sliow  that  during  the  first 
day  or  two  of  a  fast  tlie  individual  uses  proteids  and  fats  as  usual,  but 
gradually  he  uses  less  and  less  proteid  each  day.  This  was  the  ease 
in  the  fast  for  thirty  days  l)y  Succi: — • 

Fat  Used. 

Not  estimated 

170 

170 

1(53 

Here  the  stored  fats  were  the  chief  source  of  energy. 

Luxus  Consumption. 

In  Liehig's  old  theory,  the  fats  and  carbohydrates  were  sup- 
posed to  generate  heat,  whilst  the  proteids  were  muscle-builders,  and 
the  life  phenomena  were  due  to  chemical  changes  in  the  proteid. 
When  it  was  found  out  that  proteids  in  part  also  generated  heat,  it 
was  looked  upon  as  a  wasteful  use  of  good  material,  and  was  denomi- 
nated a  luxus  consum})tion. 

The  luxus  consumption  theory  of  Voit  is  that  the  excess  of  pro- 
teids in  the  blood  and  lymph  is  oxidized  in  those  fluids,  but  all 
facts  tend  to  show  that  these  proteids  are  first  built  up  into  the  cell 
before  they  are  oxidized.  Hence  we  see  there  can  be  no  dividing 
line  made  between  the  circulating  proteid  of  the  blood  and  lymph 
and  the  organ  proteid  of  the  cells. ^ 

Fats. 

Fat  passes  into  the  blood  l)y  the  thoracic  duct  and  is  soon 
removed  from  the  circulation,  for  normal  blood  only  contains  traces 
of  it.  The  quantity  of  fat  in  healthy  persons  may  vary  greatly: 
from  2.5  to  23  per  cent.  Fats  are  encountered  in  two  forms  in  the 
organism:  (a)  as  an  emulsion  in  the  nutritive  fluids;  (&)  in  drops 
in  small  particular  cells  or  in  the  interior  of  tissue-cells.  While  in 
the  emulsion  state  the  fats  are  in  circulation,  in  the  second  state 
they  are  at  rest.     The  combustion  of  fats  produces  water  and  CO.,. 

Origin  of  Fats. —  When  Munk  fed  a  dog  with  rape-seed  oil,  which 
contains  crucic  acid,  which  is  normally  not  found  in  the  body,  it 

'  Abderhalden  holds  tliat  the  aniido-acids  are  broken  up  outside  the 
cells  of  the  tissues. 


METABOLISM.  427 

could  be  found  in  the  fat  stored  away  as  body  fat.  Hence,  fat  can 
come  from  fatty  food.  Some  fat  is  also  derived  from  the  proteids. 
Fats  demand  more  oxygen  than  carbohydrates  when  they  are  meta- 
bolized. Each  gram  of  carbon  corresponds  to  1.3  grams  of  fat, 
because  fat  contains  76.5  per  cent,  of  carbon.  As  to  fat,  about  100 
grams  can  be  digested  daily. 

Fat  is  also  produced  from  the  carbohydrates.  Fats  are  used  up 
during  abstinence,  during  insufficient  diet,  or  during  sickness.  The 
fats,  when  burnt  up  by  oxygen,  form  water  and  carbon  dioxide,  the 
energy  being  transformed  into  heat  and  into  mechanical  or  chemical 
work.  Fat  is  a  steady  source  of  energy  in  work.  Hence,  a  man  who 
works  has  need  of  more  fat  than  one  who  pursues  a  sedentary  life. 

The  liver  becomes  loaded  with  fat  from  poisoning  by  phos- 
phorus. Here  the  fat  is  imported  from  other  storage  place's  in  the 
body  for  fat. 

Carbohydrates. 

They  pass  into  the  liver  by  the  portal  circulation  as  dextrose 
and  are  partly  stored  up  in  the  liver-cell  as  glycogen,  to  be  given 
off  as  sugar  in  the  periods  between  digestion,  to  be  used  up  when  a 
sudden  demand  is  made  by  the  starving  or  working  body.,  Carbo- 
hydrates may  also  be  derived  from  proteids.  The  dextrose  is  used 
up  by  the  muscle-  and  gland-cells  being  oxidized,  the  carbon  going 
off  as  carbon  dioxide.  As  to  amount  of  carbohydrates,  only  500 
grammes  can  be  consumed  without  digestive  disturbance. 

The  carbohydrates  are  found  in  small  proportion  in  flesh-foods, 
such  as  glycogen,  and  in  milk  in  the  form  of  lactose.  By  far  the 
greater  proportions  of  carbohydrates  are  obtained  from  the  vegetable 
kingdom.     In  vegetable  foods  they  occur  as  starches  and  sugars. 

An  animal  that  is  fed  upon  carbohydrates  exclusively  dies  of 
starvation  on  account  of  want  of  protcid.  The  saving  of  proteid 
increases  proportionately  with  the  quantity  of  carbohydrates  in- 
gested. This  is  an  important  fact,  since  the  digestive  juices  are 
capable  of  digesting  them  in  large  quantities. 

The  fatigue  of  muscle  is  slowed  by  the  use  of  sugar.  For  four 
days  Dr.  F.  S.  Lee  gave  animals  phloridzin,  which  sweeps  the  greater 
part  of  the  carbohydrate  material,  or  glycogen,  out  of  the  muscles. 
Then  he  irritated  the  tibialis  anticus,  and,  while  it  gave  1000  con- 
tractions per  minute  on  electrical  stimulation  normally,  after  the 
removal  of  glycogen  by  the  phloridzin  the  contractions  were  only 
from  200  to  400  per  minute.     These  experiments  proved  that  carbo- 


428  PHYSIOLOGY. 

hydrates  assisted  the  muscle  in  its  contraction.  He  made  another 
series  of  experiments  upon  the  muscles  which  had  their  glycogen 
removed  by  phloridzin,  and  then  gave  50  grams  of  dextrose.  Then 
electrical  irritations  were  used  on  the  muscles,  which  gave  560  con- 
tractions per  minute.     Here  the  glucose  restored  the  muscle. 

Water. 

Among  the  inorganic  compounds,  the  most  important,  without 
exception,  is  water.  It  is  even  more  important  than  proteid  and  fat, 
since  it  forms  about  three-fifths  of  the  weight  of  the  body. 

Water  has  an  important  function  within  the  organism.  When 
proteid  is  insufficient,  water  accumulates  in  the  tissues.  Among  the 
poorer  classes,  whose  nourishment  is  insufficient,  infectious  diseases 
flourish,  since  their  nutritive  liquids  are  excellent  media  for  the 
cultivation  of  micro-organisms. 

Excess  of  water  causes  an  augmentation  of  urea;  hence  the 
success  of  mineral  waters  in  Bright's  disease.  This  increase  of  urea 
is  due  to  the  abundant  washing  out  of  the  retarded  metabolic  acts 
through  the  kidneys. 

Salts. 

Salts  are  a  necessity  in  foods,  and  their  absence  leads  to  scurvy. 

There  is  not  any  liquid  nor  any  tissue  which  does  not  produce 
an  ash  upon  calcination.  The  inorganic  salts  are  either  in  solution 
or  combined  with  organic  substances,  notably  proteid.  The  com- 
bination of  the  various  needful  salts  with  protoplasm,  the  substratum 
of  life,  is  of  the  highest  importance.  Of  the  various  salts  found 
within  the. tissues,  sodium  chloride  is  the  most  important. 

Lime  and  Magnesia  Salts. — The  alkaline  earths,  if  in  too  great 
quantity,  may  precipitate  to  form  hepatic  calculi. 

The  phosphate  of  lime  forms  the  greater  part  of  bone.  Bone 
depends  upon  the  salts  of  lime  found  in  the  food. 

Lime  occurs  in  large  amount  in  milk.  The  only  other  food 
which  has  the  same  amount  as  milk  is  the  yelk  of  egg.  This  latter 
should  be  given  to  children  when  milk  is  not  at  hand  or  not  readily 
digested.  Withholding  lime  is  favorable  to  the  production  of  rickets. 
Calcium  is  excreted  chiefly  with  the  succus  entericus. 

Animals  from  whose  food  the  salts  have  been  extracted  very  fre- 
quently die  more  rapidly  than  animals  from  whom  food  has  been 
entirely  withheld.  There  is  caused  a  train  of  symptoms  indicating 
a  disturbance  of  the  central  nervous  apparatus  and  the  digestive  sys- 


METABOLISM.  429 

tern.  This  untoward  result  is  due  to  chronic  sulphuric-acid  poison- 
ing from  the  oxidation  of  the  sulphur  of  the  proteids. 

Now,  the  bases  in  the  blood  which  neutralize  are  the  sodium 
carbonate  and  sodium  phosphate,  and  it  has  been  estimated  that  the 
amount  of  this  alkaline  reacting  alkali  or  native  alkali  in  the  entire 
body  is  equivalent  to  60  grams  of  sodium  hydroxide  (NaOH).  This 
amount  of  alkali  is  so  small  that  it  would  be  quickly  exhausted  by  a 
persistent  acid  intoxication  with  a  persistent  formation  of  only  small 
amounts  of  acid.  Certain  diabetic  patients  pass  daily  for  long 
periods  a  large  amount  of  acids  which  are  excreted  by  the  urine  in 
combination  with  bases,  it  being  understood  that  the  urine  does  not 
contain  free  acid.  As  the  native  alkali  of  the  body  is  not  sufficient 
to  neutralize  so  much  acid,  it  is  necessary  that  there  should  be 
another  and  more  enduring  source  of  alkali  than  the  native.  For 
this  ammonia  is  generated  by  proteid  metabolism  of  the  cells,  and 
especially  of  meat.  The  acids  in  diabetes  are  the  aceto-acetic  and 
the  oxybutyric,  which  can  be  detected  in  the  urine.  Acetone  is  also 
present  in  the  urine  of  severe  diabetics.^ 

Iron. — Such  compounds  of  iron  as  are  contained  in  nuclein 
found  in  the  yelk  of  egg  have  been  termed  Bunge  hcematogens.  In 
the  chick  the  developing  red  corpuscles  obtain  their  iron  from  it. 
Iron  is  absorbed  through  the  duodenum  and  excreted  mainly  through 
the  mucous  membrane  of  the  colon.  Inorganic  and  organic  com- 
binations of  iron  are  absorbed.  Iron  is  deposited  in  lymph-ganglia, 
spleen,  and  liver. 

Composition  of  the  Body. 

An  analysis  of  the  body,  as  a  whole,  is  as  follows: — 

Water    64  per  cent. 

Proteids 16 

Fat 14 

Salts    5 

Carbohydrates    1         " 

Diet. 

The  diet  of  a  healthy  man  has  for  its  aim  not  only  to  cover  any 
deficit  without  catabolism  ceasing  and  of  maintaining  the  system  in 
a  state  of  integrity  indispensable  to  its  physiological  functions,  but 
also  to  furnish  to  the  organism  a  certain  food-reserve  so  that  the 


^Herter:  "Chemical  Pathology,"  1902. 


430 


PHYSIOLOGY. 


body  will  not  lose  its  own  proper  tissue.  To  ascertain  exactly  the 
quantity  of  nourishment  necessary  to  keep  the  body-weight  the  same 
it  is  necessary  to  have  recourse  to  experiments. 

Example  of  a  Metabolism  Investigation. 

I  have  selected  as  an  example  one  given  by  Beddard.^ 

It  is  desired  to  know  whether  a  diet  containing  125  grams  of 

proteid,  50  grams  of  fat,  and  500  grams  of  carbohydrate  is  sufficient 

for  a  man  doing  a  moderate  amount  of  work. 


Proteid  .  .  ■ 
Carbohydrate 
Fat         ... 


Intaks. 


62  grams. 
200       " 
J8       " 
300       " 


NITROGEN. 


20  grams. 

00 

00 

20  grams. 


51-2.5 
2050.0 

465.0 
3027.5 


Output. 


NITROGEN. 


In  urine  , 
In  faeces  , 
In  breath 


11  grams  (16.5X0.67) 
5       " 
254       " 
270       " 


16.5  grams. 

1.0  gram. 

0.0 

17.5  grams. 


Ketained  in  body,  30  grams  of  carbon  and  2.5  grams  of  nitro- 
gen. This  amount  of  nitrogen  represents  2.5  X  6.25  =  15.6  grams 
proteid,  or  75  grams  of  muscle.  Now,  this  amount  of  proteid  will 
account  for  8.25  grams  of  carbon;  so  that  30  —  8.25  =  21.75  grams 
of  carbon  represents  21.75  X  1-3  :=  28.3  grams  of  fat.  On  this  diet, 
therefore,  the  subject  retains  in  his  tissues  15.6  grams  proteid  and 
28.3  grams  fat  per  diem. 

To  express  this  result  in  terms  of  energy  liberated,  we  know 
that  3027.5  calories  were  supplied,  and  that  all  these  have  been  used 
except  15.6  X  4.1  =  6-1  retained  as  proteid  and  28.3  X  9.3  =  263.2 
retained  as  fat,  or,  in  toto,  327.2  C.  We  find,  therefore,  that  3027.5 
—  327.2  =  2700  C.  have  been  required. 

One  gram  of  fat  when  burned  produces  9.5  Calories. 


^  "Practical  Physiology." 


METABOLISM.  431 

One  gram  of  proteid  when  burned  produces  about  4.1  Calories. 

One  gram  of  carbohydrate  when  burned  produces  4.1  Calories. 

One  gram  of  alcohol  when  burned  produces  7  Calories. 

One  large  Calorie  equals  1000  small  calories.  The  large  Calorie 
is  written  with  a  capital  C;   the  small  calories  with  a  small  c. 

Dr.  W.  S.  Hall's  balance-sheet  for  man  at  light  work  is  as  fol- 
lows : — 

Income 
IN  Calories. 

Proteids     110  grams  x  4100    451,000 

Fat    100       "       X  9400    940,000 

Carbohydrates 400       "       x  4180    1672,000 


3,063,000 

Expenditure : — 

Expenditure 
IN  Calories. 

1.  Mechanical   work  212,750   kilogram  meters 500,000 

(425.5  gram  meters  equivalent  to  a  calorie.) 

2.  Heat  lost  in  2340  grains  of  excreta ' .       58,500 

(Cooling  from  37°  C.  to  12°  C. :   2340  x  25.) 

3.  Heat  required  to  warm  13,000  grams  of  air  from 

12°  C.  to  37°  C 84,500 

Specific  heat  of  air — 0.26: 
(13.00  x  25  X  0.26.) 

4.  Evaporating  330  grams  of  water  from  lungs  ....      192,000 

(18  grams  requires  582  calories.) 

5.  Evaporating  660  grams  of  water  from  skin  .     ...     384,000 

6.  Radiation  and  conduction  from  skin  about 184,000 


3,063,000 


Atwater  concludes  that  the  energ_y  requirements  of  the  diet  var}^ 
as  follows: — 

Calories. 

Man  without  muscular  work   2700 

Man  Avith  light  muscular  work   3000 

Man  with  moderate  muscular  work   3500 

Man  with  severe  muscular  work   4500 

Chittenden  made  experiments  upon  soldiers  and  athletes  for  six 
months.  The  118  grams  of  proteid  necessary  per  day,  according  to 
Voit,  means  at  least  16  grams  of  nitrogen  in  the  urine,  when  this 
food  is  metabolized  in  the  form  of  urea,  uric  acid,  and  purin  bases. 
Minkowski  has  shown  that  adenin,  one  of  the  purin  bases  found  in 
the  breaking  down  of  cell-nuclei,  has  a  marked  toxic  action  on  dogs 
and  man.     It  has  a  local  action  on  the  kidneys,  giving  rise  to  deposi- 


432  PHYSIOLOGY. 

tion  in  the  kidney  itself  of  spheroliths  of  uric  acid  or  urate,  which 
leads  to  acute  nephritis,  albuminuria,  and  speedy  death  of  the  ani- 
mal. The  alloxuric  bases  also  cause  fever,  when  given  by  the 
mouth  or  subcutaneously.  It  is  evident  that  the  products  of  pro- 
teid  metaljolism  are  more  or  less  dangerous  to  the  body,  especially 
so  when  there  is  an  excess  of  proteid  food  consumed.  Chittenden 
reduced  the  proteid  food  of  the  soldiers  one-half  to  one-third  of  the 
amount  ordinarily  considered  necessary.  After  the  body  had  once 
adjusted  itself  to  these  new  conditions,  the  body  weight  remained  at 
a  stationary  condition.  There  was  a  marked  increase  in  physical 
strength;  there  was  no  falling  off  in  physical  or  mental  vigor,  or 
any  change  in  the  hemoglobin  or  in  the  number  of  erythrocytes. 
Any  excess  of  proteid  over  that  which  is  really  needed  for  these  pur- 
poses causes  so  much  unnecessary  strain  upon  the  organism.  It 
imposes  a  needless  labor  on  the  excretory  organs.  Moderation  in 
the  taking  of  proteid  foods  means  a  great  saving  in  the  wear  and 
tear  of  the  body  machinery,  especially  the  kidneys  and  liver,  and  a 
lessened  production  of  uric  acid. 

Obesity  is  produced  by  all  the  causes  which  slow  the  organic  oxi- 
dations, as  sedentary  life,  absence  of  work  or  locomotion,  and  insuffi- 
ciency of  air  and  light.  Predisposing  causes  are  heredity,  anaemia, 
and  sexual  influences. 

There  is  a  method  of  reducing  obesity  known  as  Banting's 
method,  named  after  an  Englishman  of  that  name.  The  method 
is  to  eat  almost  exclusively  proteids,  the  patient  obtaining  his  fat  in 
his  body,  although  some  fat  is  produced  by  the  proteids. 

In  the  Oertel  metliod  of  treating  obesity,  the  cardiac  muscle  is 
strengthened  by  diminishing  the  amount  of  food  one-half  and  of 
water  still  more,  and  by  using  carefully-regulated  exercise.  The 
nitrogenous  foods  are  in  this  plan  increased,  and  the  non-nitrogenous 
decreased. 

Development  and  Growth. 

When  the  anabolic  and  catabolic  processes  are  balanced  in  adult 
life,  the  body  remains  the  same  in  weight. 

The  progressive  development  of  the  body  in  height  is  made  in 
an  uneven  manner,  depending  upon  different  ages.  In  the  first  year 
the  growth  is  about  twenty  centimeters,  in  the  second  year  ten  centi- 
meters, third  year  about  seven  centimeters,  from  five  to  sixteen,  about 
five  and  one-half  centimeters  each  year.  In  the  twentieth  year 
growth  is  very  slight. 


METABOLISM.  433 

Dr.  Bowditch  has  shown  that  growth  is  most  rapid  during  the 
earliest  periods  of  life.  During  the  first  twelve  years  boys  are  from 
one  to  two  inches  taller  than  girls  of  the  same  age.  At  about  twelve 
and  a  half  years  girls  begin  to  grow  faster  than  boys,  and  during 
the  fourteenth  year  are  about  one  inch  taller  than  boys  of  the  same 
age.  At  fourteen  and  a  half  years  of  age  boys  again  become  taller, 
girls  having  at  this  period  very  nearly  completed  their  growth,  while 
boys  continue  to  grow  rapidly  till  nineteen  years  of  age. 

On  the  contrary,  the  development  in  thickness  and  breadth  is 
slower  during  the  first  years  than  at  puberty;  toward  the  fortieth 
and  fiftieth  years  it  attains  its  maximum. 

The  tissues  of  the  organs  may  increase  in  two  ways :  by  increase 
in  volume  of  existing  elements  or  by  the  multiplication  of  new  cells. 

Bones  present  certain  physiological  properties  of  great  interest, 
for  they  grow  in  both  length  and  thickness.  The  increase  in  length 
is  at  each  end  of  the  bone  at  the  junction  of  the  epiphysis  with  the 
diaphysis.  The  increase  in  thickness  is  made  by  means  of  the  peri- 
osteum adding  new  layers  of  bone  on  the  surface. 


CHAPTER  X. 

ANIMAL    HEAT. 

Inorganic  bodies  have  a  constant  tendency,  either  by  losing  or 
gaining  heat,  to  adapt  themselves  to  the  temperature  of  surrounding 
media  or  objects.  They  may  be  artificially  cooled  or  artificially 
heated  to  all  possible  degrees. 

Living  plants  and  animals  also  receive  and  give  off  heat  physic- 
ally; but,  in  addition,  they  possess  a  common  power  of  resisting 
external  temperatures.  With  the  plants  this  power  is  very  feeble  in 
degree ;  with  animals  it  is  more  marked.  Among  the  higher  animals, 
especially,  is  there  an  inherent  power  to  maintain  a  temperature  that 
differs  from  that  of  the  surrounding  media.  Since  living  animals, 
like  dead  ones  and  inorganic  bodies,  exhibit  the  same  physical  plie- 
nomena  of  absorption,  conduction,  and  radiation  of  heat,  they  un- 
dergo constant  changes;  these  are  usually  in  the  direction  of  loss  of 
heat.  Hence  there  must  exist  within  them  a  power  of  constant 
renewal  or  production  of  heat  to  take  the  place  of  that  lost.  This 
function  of  producing  heat  is  universal  with  the  warm-blooded  ani- 
mals, and  all  of  the  processes  of  life  are  influenced  by  it.  Certainly 
the  higher  animals  have  within  their  bodies  not  only  some  means  to 
produce  heat,  but  some  mechanism  whereby  the  production  and  loss 
are  regulated.  Thus,  though  the  temperature  of  the  surrounding 
atmosphere  be  very  high,  as  in  luidsummer,  or  very  low,  as  in  mid- 
winter, yet  the  standard  temperature  of  the  animal's  body  remains 
uniform  and  constant.  The  energy  necessary  to  accomplish  this  is 
known  as  animal  heat. 

Physical  Heat. — Heat  is  a  form  of  energy  exhibited  by  matter. 
We  cannot  create  or  destroy  either. 

Energy  is  the  power  to  do  work.  Any  agent  that  is  capable  of 
doing  work  is  said  to  possess  this  property.  The  quantity  of  energy 
that  it  possesses  is  measured  by  the  amount  of  work  it  can  do.  When 
a  body  is  hot  it  possesses  a  store  of  energy  which  may  be  exhibited  by 
the  heated  matter. 

Energy  is  known  in  tvw  forms:  1.  The  energy  possessed  by  a 
body  in  consequence  of  its  velocity  is  known  as  energy  of  motion,  or 
Icinetic  energy.  The  body  in  motion  which  has  this  kinetic  energy 
(434) 


ANIMAL  HEAT.  435 

communicates  it  to  some  other  body  during  the  process  of  bringing  it 
to  rest.     This  is  the  fundamental  form  of  energy. 

2.  The  other  form  of  energy  which  a  body  may  have  depends  not 
upon  its  own  state,  but  upon  its  position  with  respect  to  other  bodies. 
It  is  the  energy  possessed  by  a  mass  in  consequence  of  its  having 
been  raised  from  the  ground.  Potential  energy  can  exist  in  a  body, 
all  of  whose  parts  are  at  rest. 

Eubner  and  Atwater  have  shown  that  the  law  of  conservation  of 
energy  is  also  applicable  to  the  living  body.  The  metabolism  of  the 
food  and  tissues  liberates  their  stored  energy  and  converts  it  into 
heat  and  motion. 

Radiant  heat  is  one  and  the  same  thing  as  that  which  we  call 
light.  When  detected  by  the  thermometer  or  by  the  sensation  of  heat, 
it  is  called  radiant  heat. 

When  equal  weights  of  quicksilver  and  water  are  mixed  together, 
the  resulting  temperature  is  not  the  mean  of  the  temperature  of  the 
ingredients.  The  effect  of  the  same  quantity  of  heat  in  raising  the 
temperature  of  two  bodies  depends  not  only  on  the  amount  of  matter 
in  the  bodies,  but  also  upon  the  kind  of  matter  of  which  each  is 
formed.     This  is  called  capacity  of  heat,  or  specific  heat. 

The  capacity  of  a  body  for  heat  is  the  number  of  units  required 
to  raise  that  body  one  degree  of  temperature.  The  specific  heat  of 
a  body  is  the  ratio  of  the  quantity  of  heat  required  to  raise  that  body 
one  degree  to  the  quantity  required  to  raise  an  equal  weight  of  water 
one  degree. 

Latent  heat  is  the  quantity  of  heat  that  must  be  communicated 
to  the  body  in  a  given  state  to  convert  it  into  anotlier  state  without 
changing  the  temperature.     Avery  describes  it  as  follows: — 

The  latent  heat  of  a  substance  is  the  quantity  of  heat  that  is 
lost  to  thermometric  measurement  during  liquefaction  or  vaporation, 
or  the  amount  of  heat  that  must  be  communicated  to  a  body  to 
change  its  condition  without  changing  its  temperature. 

The  higher  the  temperature  of  a  body,  the  greater  is  its  radi- 
ation. When  the  temperature  of  bodies  is  unequal,  the  hotter  bodies 
will  emit  more  heat  by  radiation  than  they  receive  from  the  colder. 
Therefore,  on  the  whole,  heat  will  be  lost  by  hotter  and  gained  b} 
colder  bodies  until  thermal  equilibrium  is  attained. 

The  cause  of  heat  is  popularly  explained  to-day  by  what  is  known 
as  the  "undulatory  theory."  According  to  this  doctrine  the  heat  of 
a  body  is  caused  by  an  extremely  rapid  oscillating  or  vibratory  motion 
of  its  molecules.     The  hottest  bodies  are  those  in  which  the  vibra- 


436  PHYSIOLOGY. 

tions  have  both  the  greatest  velocity  and  the  greatest  amplitude. 
Hence,  heat  is  not  a  substance,  but  a  condition  of  matter.  It  is  a 
condition  which  can  be  transferred  from  one  body  to  another.  When 
a  heated  body  is  placed  in  contact  with  a  cooler  one,  the  former  gives 
more  molecular  motion  than  it  receives;  but  the  loss  of  the  former 
is  the  equivalent  of  gain  of  the  latter. 

Animal  Heat. — Within  the  organs  of  the  human  body,  as  well  as 
those  of  all  animals,  processes  of  oxidation  are  continually  going  on. 
Oxygen  passes  through  the  lungs  into  the  blood  to  be  thus  carried  to 
all  parts  of  the  body.  In  like  manner  the  oxidizable  bodies,  which 
are  principally  foods,  pass  by  the  processes  of  digestion  into  the 
blood  finally  to  reach  every  part  of  the  body.  The  gases,  liquids, 
and  solids  which  enter  the  body  are  loaded  with  energy.  These 
various  bodies  are  intimately  concerned  in  the  different  chemical 
processes  which  sum  up  metabolism:  that  is,  those  phenomena 
whereby  living  organisms  are  capable  of  incorporating  into  their  tis- 
sues, substances  obtained  from  their  food.  Metabolism  is  also  con- 
cerned in  the  formation  of  a  store  of  potential  energy  which  may 
readily  be  transformed  into  Jcineiic  energy,  as  manifested  in  muscular 
work  and  heat.  Within  the  body  the  assimilable  substances  undergo 
many  chemical  changes,  and  finally  leave  it  in  forms  quite  different 
from  those  on  entering  it.  The  oxygen  inspired  combines  mainly  with 
carbon  and  hydrogen  to  form  carbon  anhydride  and  water,  while  the 
more  complicated  compounds  are  reduced  to  simple  bodies,  to  be 
excreted  as  such.  In  the  process  of  disintegrating  these  compounds 
— in  fact,  in  catabolism  in  general — one  of  the  most  important  re- 
sults is  the  production  of  heat.  The  energy  enters  the  body  as  poten- 
tial energy  stored  up  in  the  food.  By  chemical  processes  it  becomes 
evolved  into  kinetic  energy  and  heat.  Animal  heat  is  the  accompani- 
ment of  the  formation  of  carbonic  acid,  urea,  and  other  excreted 
products.  According  to  our  theory  of  heat,  the  animal  heat  due  to 
metabolic  processes  must  represent  to  us  vibrations  of  the  corporeal 
atoms. 

Other  Sources. — Roughly  speaking,  the  muscles  constitute  about 
one-half  of  the  whole  mass  of  the  body,  the  bones  the  other  half.  As 
but  little  oxidation  occurs  in  the  bones,  the  muscles  must  be  the 
chief  seat  of  heat-production.  Muscular  exercise  greatly  increases 
the  metabolism  and  the  COo  excreted,  but  there  is  an  accompanying 
increase  in  heat-production.  In  health  the  muscles  yield  four-fifths 
of  the  body  heat. 

The  secreting  glands  are  known  to  be  centers  of  thermogenesis 


ANIMAL  HEAT.  437 

as  well.  The  alimentary  canal  during  digestion  and  also  the  liver  are 
very  marked  sources.  In  fact,  the  blood  in  the  hepatic  veins  is  the 
warmest  part  of  the  body.  The  function  of  the  muscles,  tendons, 
ligaments,  and  bones  is  not  a  very  slight  source  6f  warmth. 

It  must  be  borne  in  mind  by  the  student  that  the  processes  of 
oxidation  are  concerned  not  only  in  the  combustion  of  the  digested 
foodstuffs,  but  also  of  the  cells  of  the  body.  It  is  the  oxidation  of 
their  protoplasm  that  evolves  warmth. 

Warm-blooded  and  Cold-blooded  Animals. — Depending  upon  the 
relationship  of  the  temperature  of  the  animal's  body  and  that  of 
the  enveloping  media  there  are  two  great  classes:  JiomotJiermal  and 
poikilothermal. 

The  homothermal,  or  warm-blooded,  animals  include  the  higher 
orders  of  the  animal  kingdom,  in  whom  the  temperature  remains 
fairly  constant  despite  variations  in  temperature  of  the  enveloping 
media.  The  temperature  of  this  class  of  animals  is  high,  but  uni- 
form. Should  homothermal  animals  remain  for  a  considerable 
length  of  time  in  a  cold  medium,  their  heat-producing  organs  become 
more  active  in  order  to  compensate  for  that  lost  rapidly  by  radiation. 
When  they  remain  in  very  warm  media,  heat-production  is  dimin- 
ished. 

Poikilothermal,  or  cold-blooded,  animals  constitute  that  class  of 
lower  animals  whose  temperature  bears  a  very  intimate  relationship 
and  is  dependent  upon  that  of  the  enveloping  media.  Their  tem- 
perature is  thus  subject  to  very  considerable  variations,  although  it 
is  always  slightly  above  that  of  its  surroundings.  When  the  tempera- 
ture of  the  surrounding  medium  is  raised,  the  amount  of  heat  pro- 
duced within  poikilothermal  animals  is  increased.  Inversely,  when 
the  enveloping  temperature  falls,  the  heat-production  within  the  ani- 
mal is  diminished.  This  class  includes  reptiles,  amphibians,  fish,  and 
most  invertebrates. 

However,  the  line  of  demarkation  between  the  two  classes  of 
animals  is  not  a  very  clear  and  decisive  one.  For  there  are  some 
animals,  as  the  bat  and  dormouse,  which  seem  to  be  intermediary. 
In  summertime  they  possess  a  high  temperature  that  is  independent 
of  their  surroundings;  in  winter  they  become  dormant  and  hiber- 
nate. While  in  this  latter  condition  their  temperature  varies  with 
that  of  the  enveloping  medium. 

Temperature  of  Man. — Although  the  blood  in  circulation  tends 
to  distribute  the  heat  of  the  body  uniformly,  yet  there  are  found 
slight  variations  in  different  regions.    These  regions  are  principally 


438 


PHYSIOLOGY. 


iijion  tlio  surface,  where  exposure  is  such  that  the  leveling  function 
of  the  blood  is  hindered.  The  mean,  daily  temperature  of  a  healthy 
man  varies  between  98°  and  99°  F.  In  the  rectum  it  is  98.96°  F.; 
in  the  axilla,  98.45°  F.;  in  the  mouth,  98.30°  F.  These  fibres 
represent  the  averages  obtained  from  various  observations,  but  they, 
too,  are  subject  to  various  variations  from  exercise,  rapid  respiration, 
food  within  the  alimentary  tract,  etc. 

From  frequent  observations  and  numerous  tables  it  will  be 
found  that  the  mean  rectal  temperature  of  other  mammals  is,  for  the 
most  part,  higher  than  that  of  man.  In  tiie  case  with  birds,  the 
temperature  averages  from  two  to  three  degrees  higher  than  that  of 
mammals.     In  securing  these  observations  it  is  always  necessary  that 


7       8      9  '10  ■  ir  12'    1       1     3   '  ^     5 


Fi 


10      1:      12     1       2    '  3 


179. — Variations  in  the  Bodily  Temperature  during 
within  Twenty-four  Hours.      (Landois.  ) 

L according  to  v.  Liebermeister.    J— 


Health 


according  to  Jiirgensen. 

the  animal  should  not  struggle  either  before  insertion  or  during  the 
time  that  the  thermometer  is  in  position.  A  faulty  reading  of  as 
much  as  three  degrees  may  occur  when  the  animal  struggles  or  has 
been  previously  chased. 

Hibernation. — Many  animals  regularly  at  the  approach  of  cold 
weather  gradually  lose  their  activities  until  they  apparently  have 
lost  all  of  their  functions  and  are  dormant.  Such  a  state  is  known 
as  hibernation.  The  temperature  of  the  animal's  body  is  but  a  trifle 
above  that  of  the  surrounding  atmosphere.  The  respirations  are 
greatly  decreased  in  number,  while  the  rhythm  is  of  the  Cheyne- 
Stokes  type.  The  heart's  action  in  point  of  force  and  frequency  is 
much  reduced  during  hibernation.  Animals  whose  hearts  during 
active  life  beat  one  hundred  or  more  now  register  but  fourteen  or 


ANIMAL  HEAT.  439 

sixteen  per  minute.  The  digestive  powers  are  at  a  very  low  ebb, 
while  as  to  its  nervous  sensibilities  the  animal  is  very  markedly 
depressed. 

The  awakening  from  hibernation  is  a  most  interesting  phenom- 
enon in  so  far  as  the  rise  of  the  animal's  temperature  is  very  sud- 
den. So  sudden  is  the  rise  and  in  so  short  a  time  is  it  accomplished 
that  it  surpasses  the  most  rapid  rise  in  temperature  of  any  fever. 
With  proportionate  celerity  are  the  vital  functions  spurred  on  to 
activity. 

Modifying  Influences. — Close  observation  shows  that  there  occur 
slight  variations  in  man's  daily  temperature.  It  is  found  to  rise 
during  the  late  morning  and  afternoon;  to  fall  during  the  evening 
and  early  morning.  Because  of  differences  in  age  of  subjects,  modes 
of  living,  climate,  etc.,  observers  are  not  agreed  as  to  the  maximum 
and  minimum  temperatures.  However,  it  may  be  safe  to  say  that 
the  maximum  temperature  is  attained  about  from  3  to  5  o'clock  in 
the  afternoon,  while  the  minimum  is  registered  at  from  3  to  5  o'clock 
in  the  morning.     The  range  of  difference  averages  about  1°  C. 

Causes. — Probably  the  two  most  important  causes  for  these  nor- 
mal variations  are  muscular  activity  and  food-ingestion.  It  is  during 
the  day  that  man,  as  a  rule,  is  most  active  and  it  is  then  that  he 
usually  replenishes  the  waste  of  his  body  by  the  consumption  of  a 
proper  amount  of  food.  Naturally  he  will  be  most  inactive  during 
the  night ;  his  bodily  functions  will  be  depressed  at  that  time  so  that 
just  so  much  heat  will  be  generated  as  the  economy  needs. 

It  has  been  found  that  the  maximum  and  minimum  points  of 
temperature  in  man  can  be  inverted.  Thus,  if  a  man  change  his 
mode  of  life  so  that  he  continue  to  work  for  a  considerable  length  of 
time  at  night  and  sleep  in  the  daytime,  after  a  week's  time  there  will 
be  noted  a  gradual  change  toward  inversion.  It  is  well  to  note  also 
that  the  high  and  low  points  of  temperature  of  the  body  correspond 
to  those  times  when  the  external  temperature  is  high  and  low,  respec- 
tively.    Eadiation  may  thus  be  a  not  inconsiderable  factor. 

Age. — Just  before  birth  the  infant's  temperature  is  generally 
somewhat  higher  than  that  of  its  mother's  uterus.  After  birth  and 
during  the  first  few  weeks  the  temperature  remains  fairly  constant, 
but  still  a  little  high.  There  is  a  fall  of  one-tenth  or  two-tenths 
from  infancy  to  puberty;  a  like  amount  from  the  latter  period  to 
middle  life,  when  there  occurs  a  slight  rise. 

During  muscular  work  the  temperature  rises  rapidly,  but,  by 
reason  of  compensatory  measures,  the  loss  by  radiation  and  conduc- 


440  PHYSIOLOGY. 

tion  is  almost  proportionately  increased.  So  nearly  are  the  genera- 
tion and  loss  balanced  that  during  actual  work  there  is  registered 
but  a  rise  of  a  degree  and  a  fraction.  With  the  conclusion  of  the 
muscular  activity  the  temperature  very  rapidly  falls  to  normal. 
Mental  work  causes  a  rise  of  both  the  general  as  well  as  local  tem- 
perature of  the  brain  and  head.  The  increase  registered  is  usually 
about  0.1°  C. 

Food  causes  a  very  slight  rise  in  temperature;  sleep,  in  itself, 
has  no  effect.  Inactivity  is  a  very  marked  factor  in  producing  a  fall. 
As  inaction  is  very  prominent  during  sleep,  the  latter  has  been 
erroneously  given  the  credit  for  causing  the  drop  in  temperature. 
Lying  perfectly  quiet  will  produce  identical  results.  Because  of  the 
heat,  the  inhabitants  of  tropical  countries  possess  a  slightly  higher 
temperature.     The  difference  is  less  than  1°  C. 

Extremes  of  Temperature. — During  excessively  hot  spells  in 
summertime  when  the  temperature  of  the  enveloping  atmosphere  is 
considerably  above  that  of  the  normal  body-temperature,  it  is  remark- 
able to  find  that  the  temperature  of  the  body  has  not  been  raised  one 
degree.  This  result  is  mainly  accomplished  by  reason  of  the  heat 
extracted  from  the  body's  surface  during  evaporation. 

The  limit  of  extreme  cold  is  reached  when  the  lymph  within  the 
animal's  tissues  is  frozen.  Fishes  have  been  incased  within  ice  and 
then  found  completely  recovered  upon  being  thawed  out  and  placed 
in  a  warmer  medium.  Normally,  the  range  of  temperature  in  a  man 
is  about  1°  C.  However,  drunkards  have  been  known,  after  exposure 
to  extreme  cold,  to  have  a  bodily  temperature  as  low  as  24°  C.  with, 
out  fatality. 

Cases  of  temperature  as  high  as  45°  C.  have  been  noted  and  yet 
recovery  has  taken  place.  Experimentally,  Bernard  found  that, 
when  the  internal  temperature  of  rabbits  was  raised  to  45°  C,  they 
died.  According  to  his  view,  death  occurred  as  the  result  of  stop- 
page of  the  heart  from  the  hot,  circulating  blood,  causing  rigor 
mortis  of  the  musculature  of  this  organ. 

Temperature  of  the  Blood. — The  average  temperature  of  the 
blood  is  39°  C,  but  there  are  found  numerous  variations  in  different 
regions.  The  blood  of  the  superficial  veins  is  cooler  than  that  of 
the  internal  veins,  due  to  prolonged  exposure  while  traversing  the 
course  of  the  former.  The  warmest  blood  of  the  body  is  that  of  the 
hepatic  veins.  The  blood  in  the  veins  is  cooler  than  the  blood  in  the 
corresponding  arteries,  due  to  the  more  superficial  position  of  the 
former.     The  temperature  of  the  blood  of  the  left  heart  is  some- 


ANIMAL  HEAT.  441 

what  lower  than  that  of  the  right.  This  has  been  explained  on  the 
ground  that  the  right  heart  is  in  closer  proximity  to  the  warm  liver; 
also,  that  the  blood  going  to  the  left  heart  has  been  cooled  from  its 
passage  through  the  lungs  during  respiration. 

Estimation  of  Temperature. — Our  knowledge  as  to  difference  in 
degree  of  the  heat  of  the  same  or  different  bodies  is  gained  by  ther- 
mometry. Thermometers  are  instruments  for  measuring  tempera- 
tures. Their  principle  is  based  upon  the  physical  phenomenon  of 
expansion  of  hodies  hy  heat.  Liquids  are  best  suited  for  this  purpose. 
Mercury  and  alcohol  are  the  only  two  liquids  used. 

The  mercurial  thermometer  is  the  one  most  extensively  used. 
It  consists  of  a  capillary  glass  tube,  at  the  end  of  which  is  blown  a 
hulh.  Both  the  bulb  and  portion  of  the  tube  are  filled  with  mercury. 
The  expansion  of  the  mercury  is  registered  by  a  scale  which  is  grad- 
uated either  upon  the  stem  itself  or  upon  a  frame  to  which  it  is 
attached.  On  the  Continent,  and  more  especially  in  France,  the 
stem  is  divided  into  one  hundred  parts,  or  degrees;  this  division  is 
known  as  the  Centigrade  scale.  In  England,  Holland,  and  North 
America  the  Fahrenheit  scale  is  used.  Its  stem  is  divided  into  two 
hundred  and  twelve  degrees  between  zero  and  the  boiling-point  of 
water. 

Estimation  of  Heat. — Calorimetry  is  the  measuring  of  the  quan- 
tity of  heat  which  results  from  the  transformation  of  energy.  By  it 
is  learned  the  amount  of  heat  possessed  by  any  body,  and  what 
amount  of  heat  the  latter  is  capable  of  producing.  Calorimetric 
measurements  are  expressed  in  thermal  units.  A  certain  quantity  of 
heat  with  which  all  other  quantities  are  compared  is  known -as  a 
thermal,  or  heat,  unit. 

A  thermal  unit  is  the  quantity  of  heat  required  to  raise  a  definite 
quantity  of  water  from  one  defined  temperature  to  another  defined 
temperature.  A  particular  thermal  unit  has  been  called  by  some 
authors  a  Calorie.  It  is  the  quantity  of  heat  necessary  to  raise  a 
kilogram  (2.2  pounds)  of  water  1°  C.  An  English  heat  unit  is  the 
quantity  of  heat  required  to  elevate  one  pound  of  water  1°  F.  One 
Calorie  equals  3.96  English  heat  units.  In  Germany  scientists  fre- 
quently use  the  word  calorie,  but  mean  the  gram-calorie.  It  repre- 
sents the  quantity  of  heat  that  is  required  to  elevate  the  tempera- 
ture of  1  gram  of  water  1°  C. 

The  whole  science  of  animal  heat  is  founded  upon  thermometry 
and  calorimetry,  as  well  as  the  indirect  method  of  calculating  the 
quantity  of  heat  produced  from  the  quantity  of  nutritive  materials 


442 


PHYSIOLOGY. 


that  have  been  consumed.  There  are  various  types  of  calorimeters 
in  existeiico,  hut  it  has  only  been  within  the  past  few  years  that 
results  at  all  exact  have  been  attained. 

The  calorimeter  employed  by  the  author  In  his  laboratory  experi- 
ments is  constructed  as  follows:  It  is  composed  of  two  cylinders  of 
galvanized  iron^ — one  smaller  than  the  other  and  inclosed  within  the 
larger.  The  sjjace  in  which  the  man  lies  upon  a  mattress  is  six  feet 
long  and  two  feet  in  diameter.  Air  is  conveyed  to  him  through  the 
tube  (H)  which  traverses  the  whole  length  of  the  apparatus  to  enter 
the  hollow  tube  of  lead  at  F;  it  finally  emerges  at  B,  after  having 
given  off  its  heat  to  the  water  between  the  two  cylinders.  The 
meter  (M)  is  run  by  the  water-wheel  (N),  which  aspirates  the  air 
through  the  entire  a])paratus  by  means  'of  a  hose  (R)  connecting  it 
with  the  lead  tube  at  B. 


Fig.    180. — Human   Calorimeter. 


The  space  between  the  cylinders  is  filled  with  about  484  pounds 
of  water.  This  water  is  kept  thoroughly  mixed  by  means  of  the  agi- 
tator (0),  which  has  two  arms.  The  arms  are  pushing  the  water 
back  and  forth  thirty  times  a  minute,  the  motion  being  caused  by  the 
electrical  motor  (X),  whose  wheel  (3),  with  its  eccentric,  drives  the 
agitator.  The  thermometer  (A)  gives  the  temperature  of  the  water; 
because  of  the  thorough  mixing  of  the  water  by  the  agitator  it  gives 
an  accurate  record  of  the  temperature  of  the  water  throughout  the 
apparatus.  The  thermometer  is  pushed  down  farther  than  is  repre- 
sented in  the  illustration.  It  usually  lies  aside  of  the  tube(H').  The 
air-tube  (B)  also  has  a  thermometer  to  denote  the  temperature  of 
the  air  as  it  is  heated  by  the  man.  The  thermometer  at  B  is  grad- 
uated into  tenths,  while  that  at  A  is  graduated  into  fiftieths.  The 
markings  are  so  far  apart  that  one  one-hundredth  of  a  degree  Fah' 
renheit  can  be  read. 


ANIMAL  HEAT.  443 

The  temperature  of  the  mouth  is  taken  by  a  thermometer  grad- 
uated into  tenths.  The  rectal  temperature  is  preferable  because  of 
accuracy.  The  bucket  (/)  receives  the  water  from  the  motor  (Z), 
and  so  conveys  it  to  the  water-wheel  {H)  that  runs  the  meter  as  an 
aspirator.  The  meter  is  hlled  with  water,  and  belongs  to  Voit's  little 
respiration  apparatus.  The  quantity  of  air  that  is  aspirated  within  an 
hour  is  from  5000  to  6000  liters,  which  is  ample  for  respiratory  pur- 
poses. The  instrument  is  made  air-tight  by  means  of  the  door  {K), 
which  is  lined  at  its  outer  edge  with  rubber.  The  whole  apparatus  is 
inclosed  in  over  six  inches  of  sawdust,  the  door  (A')  having  against 
it  a  sawdust  mattress. 

The  door  is  bound  by  eight  powerful  screw-clamps.  The  air 
enters  the  tube  {H),  then  passes  through  a  leaden  tube  that  is  coiled 
upon  itself  before  it  reaches  the  person  lying  upon  the  mattress. 

I  have  tested  the  calorimeter  before  and  after  the  performance 
of  my  experiments. 

The  interior  of  the  instrument  is  lighted  up  by  an  Edison  incan- 
descent light  of  one-candle  power.  The  patient  is  thus  enabled  to 
spend  his  time  in  reading  a  book  while  the  experimenter  is  making 
his  observations. 

By  placing  a  pulley  outside  the  calorimeter  and  attacliing  to  a 
leather  rope  a  fourteen-pound  weight,  the  man  within  the  instrument 
is  able  to  exercise.  The  leather  band  enters  one  of  the  air-holes  of 
the  instrument.  Of  the  entire  amount  of  heat  dissipated,  about 
IJf.  per  cent,  is  thrown  off  by  the  lungs. 

My  little  calorimeter  is  constructed  upon  the  same  plan  as  the 
instrument  for  men.  In  this — the  animal  calorimeter — the  agitator 
sits  astride  the  inner  cylinder,  outside  of  the  leaden  coils,  and  is  run 
at  the  rate  of  sixty  to  seventy  movements  per  minute  by  means  of  a 
water-motor.  In  other  instruments  the  water  is  occasionally  agitated 
by  means  of  a  hand-contrivance.  Instead  of  the  air  entering  the 
inner  chamber  by  a  straight  tube,  it  traverses  a  tube  coiled  upon 
itself  in  the  water  reservoir  of  the  instrument  to  enter  the  inclosure 
at  its  base.  The  air  emerges  through  the  opening  at  the  top  to  be 
carried  out  through  the  serpentine  coil  and  thence  through  the 
aspirating  meter.  The  latter  records  at  the  same  time  the  amount 
of  air.  The  constant  activity  of  the  agitator  causes  the  heat  to  be 
equally  diffused  through  the  water  and  so  permits  none  to  be  given 
to  the  air.  The  door  swings  upon  a  hinge.  In  its  center  there  is  a 
glass  through  which  one  can  readily  see  the  state  of  the  animal  or  the 
apparatus  connected  with  it.     At  its  edge  it  is  lined  with  rubber  and 


444  PHYSIOLOGY. 

closed  by  powerful  iron  screw  clamps.  In  front  of  the  door  is  a  mat- 
tress of  sawdust  several  inches  thick.  Over  and  around  the  calori- 
meter, instead  of  the  usual  sawdust  or  felt,  I  used  the  packing  mate- 
rial of  wood-fiber  known  as  excelsior.  The  whole  instrument  is 
inclosed  within  a  box  which  has  a  door. 

The  calorimeter  is  sixteen  inches  in  length  and  twelve  inches 
in  diameter.  The  instrument  has  a  circular  opening  through  which 
a  thermometer  graduated  to  one-fiftieth  of  a  degree  Fahrenheit  passes 
into  the  water.  An  opening  is  also  provided  in  the  air-tube  into 
which  a  thermometer  can  be  inserted. 

This  instrument  is  fairly  exact.  By  calculation  it  is  found  that 
the  error  is  5.4  per  cent.  After  the  performance  of  numerous  experi- 
ments it  was  found  that  the  variations  from  this  number  were  within 
1  per  cent.  Hence  it  may  be  assumed  that  this  is  an  instrument  of 
precision.  For  absolute  accuracy  the  moisture  of  the  air  and  the 
barometric  correction  should  be  made,  but  they  would  not  alter  the 
result  very  perceptibly.  The  instrument  is  always  used  with  the  air 
a  degree  or  so  above  the  temperature  of  the  calorimeter.  The  agi- 
tator is  set  in  motion  for  a  half-hour  before  the  observation  is  com- 
menced. The  room  temperature  for  twenty-four  hours  previously  is 
kept  the  same.  With  these  precautions  the  instrument  works  ac- 
curately. 

By  the  calorimeter  we  are  enabled  to  measure  the  transforma- 
tion of  the  potential  energy  of  the  food  into  heat  and,  at  the  same 
time,  measure  the  number  of  heat  units  produced.  The  total  amount 
of  energy  present  in  the  human  body  might  be  measured  by  com- 
pletely burning  an  entire  human  body  in  a  calorimeter.  By  this 
means  it  may  be  determined  how  many  heat  units  are  produced  when 
it  is  reduced  to  ashes. 

If  a  man  were  not  supplied  with  food  he  would  lose  fifty  grams 
of  his  body-weight  every  hour.  This  is  due  to  the  constant  oxidation 
which  occurs,  whereby  the  materials  of  the  body  unite  with  the  in- 
spired and  circulating  oxygen  to  produce  combustion  and  heat. 

It  is  known  that  any  given  oxidation  will  always  produce  the 
same  amount  of  heat.  Thus,  if  a  gram  of  fat  be  burned  in  a  calorim- 
eter there  will  be  produced  a  certain  and  almost  unvarying  number 
of  heat  units.  By  numerous  experiments  upon  foodstuffs  it  has  been 
determined  by  the  calorimeter  just  the  number  of  heat  units  a  gram 
of  each  will  yield.  Just  as  in  the  calorimeter,  only  far  more  slowly, 
are  the  foodstuffs  within  our  bodies  burned  up.  That  is,  the  presence 
of  oxygen  transforms  the  potential  energy  within  them  into  kinetic. 


ANIMAL  HEAT. 


445 


Should  the  voluntary  activities  be  at  rest,  the  major  portion  of  this 
energy  is  transformed  into  heat.  The  same  number  of  heat  units 
would  be  produced  within  the  body  as  within  the  calorimeter,  pro- 
vided the  foodstuffs  were  completely  oxidized.  However,  we  know 
that  every  gram  of  proteid  yields  one-third  of  a  gram  of  urea  during 
combustion  within  the  body.  The  urea  has  a  heat  value  of  its  own, 
so  that  the  real  number  of  heat  units  obtained  by  body-combustion 
is  considerably  less  than  that  of  calorimeter  combustion  of  proteids. 


RTT. 


io8« 


ic6° 


360  300  340 

Minutes,  first  da]^ 

Fig.  181. — Bilateral  Puncture  of  the  Tuber  Cinereura  of  Rabbit 

Through  Roof  of  Mouth. 

The  units  obtained  from  body  or  tissue  combustion  represent  a 
"physiologic  heat-value";  those  gained  from  the  calorimeter,  a 
"physical  heat-value." 

A  man  produces  daily  a  quantity  of  heat  equal  to  about  2800 
calories. 

Regulation  of  Temperature. — That  the  regulation  of  the  tem- 
perature cannot  be  accomplished  solely  by  the  action  of  the  circula- 
tion, respiration,  vasomotor,  and  sudorific  centers,  is  shown  by  the 
following  facts:  (1)  If  a  puncture  is  made  through  the  roof  of  the 
mouth  of  a  rabbit  with  a  guarded  dental  drill  and  the  tuber  einereum 
is  only  slightly  grazed,  the  animal  will  fall  at  your  feet,  dead,  in  five 


446 


PHYSIOLOGY. 


minutes.     If  now  the  temperature  is  taken,  it  will  be  found  to  be 
109Vo°  F.     Here  there  is  a  sudden  arrest  of  the  circulation,  respira- 


i 


«0      \o       lo        vr> 

Respiration. 

Fig.   182. — Puncture  of  Tuber   Cinereum   in  Rabbit,   Showing  Effect  on 
Respiration,  Arterial   Tension,  Pulse,  and  Temperature. 

At  the  end  of  90  minutes  the  animal   was   unbound,    when   a  rise  occurred  in 
curve  of  respiration. 

tion,  and  vasomotor  action,  in  fact  a  rapid  death,  still  the  tempera- 
ture rises  to  109.5°  F.    ISfow,  if  by  a  puncture  of  the  medulla,  pons, 


ANIMAL  HEAT.  447 

or  crura  cerebri,  sudden  death  ensues;  3'et  the  temperature  is  but 
slightly  increased.  These  facts  show  that  the  injury  of  the  tuber 
determines  a  rise  of  temperature  by  some  action  on  the  metabolism 
of  the  body.  (3)  When  a  rabbit  is  bound  down  and  the  respiration, 
blood-pressure,  and  pulse  are  recorded  on  the  kymograph,  and  the 
thalamus  punctured,  then  the  temperature  records  its  highest  point 
at  the  time  when  the  respiration,  arterial  tension,  and  pulse-rate  are 
falling. 

In  a  transverse  section  of  the  corpora  striata,  I  have  seen  a  tem- 
perature of  110°  F.  and  the  animal  die  inside  of  five  minutes. 
Hence  we  must  attribute  the  regulation  of  temperature  to  special 
thermogenic    and   thermo-inhibitory   centers. 

Thermotaxic  Centers. — These  centers  compose  the  thermogenic, 
thermo-inhil)itory,  and  thermolytic  centers,  as  the  aim  of  all  is  to 
regulate  the  temperature. 

Thermogenic  Centers. — Spinal  Cord. — Destruction  of  the 
spinal  cord  from  the  fifth  dorsal  vertebra  down  j^ermits  the  animal 
to  generate  as  much  heat  as  before  the  operation.  A  drug,  beta- 
tetrahydronaphthylamin,  when  injected  by  the  vein  causes  a  great 
increase  of  temperature,  l)ut  after  a  section  behind  the  tuber  cinereum 
it  fails  to  cause  any  rise  of  temperature.  These  facts  lead  to  the 
conclusion  that  there  are  no  special  thermogenic  centers  in  the  spinal 
cord,  but  that  the  basal  thermogenic  centers  act  through  the  trophic 
centers  in  the  anterior  cornua. 

Brain. — When  a  normal  animal  is  subjected  to  heat  or  cold  it 
regulates  its  temperature  and  keeps  it  at  a  fixed  point.  If.  however, 
the  spinal  cord  is  separated  from  the  brain,  the  spinal  cord  is  not 
able  to  regulate  the  temperature  at  a  given  degree,  but  its  tempera- 
ture changes  with  the  temperature  of  the  surrounding  air.  These 
facts  show  also  the  importance  of  the  thermotaxic  centers  in  the 
brain  in  the  regulation  of  temperature. 

As  to  the  medulla  oblongata  and  pons,  numerous  punctures  by 
a  probe  two  millimeters  in  width  and  one  millimeter  in  thickness 
caused  a  very  slight  rise  of  temperature,  which  was  of  a  very  fugitive 
nature.  Cross-section  of  the  pons  is  an  operation  which  cuts  off  the 
afferent  and  efferent  fibers  from  the  tliermotaxic  centers  anterior  to 
it  and  permits  heat-production  to  increase  without  any  regulation. 
If  there  are  any  thermogenic  centers  in  the  pons,  puncture  ought  to 
bring  out  the  fact,  as  it  has  done  for  the  thermogenic  centers  located 
in  the  basal  ganglia. 

Any  transverse  section  behind  the  crura  cerebri  or  pons  simply 


448  PHYSIOLOGY. 

cuts  out  the  thermogenic  and  tliermo-inhibitory  centers  in  front  of 
the  section  and  permits  the  thermic  apparatus  beliind  the  section  to 
elevate  the  temperature.  That  a  greater  rise  of  temperature  should 
ensue  after  pontal  than  after  crural  section  is  quite  in  accord  with 
the  well-known  fact  that  successive  sections  from  before  backward 
cause  a  greater  activity  of  the  spinal-cord  centers  behind  the  section, 
and  also  of  the  trophic  centers. 


Fig.   18.3— Cortex   of  Cat's   Brain. 

g.  Cruciate  thermo-inhibitory  center  of  Eulenberg  and  Landois.     S,   Sylvian 
tliermo-inliibitory  center  of  Ott. 

Now,  I  have  shown  that  after  the  intravenous  injection  of  beta- 
tetrahydronaphthylamin  in  the  normal  animal  a  great  rise  of  tem- 
perature ensues.  But  after  section  through  the  crura  cerebri  this 
drug  is  powerless  to  raise  the  temperature.  A  needle-point  thrust 
into  the  pons  or  crura  causes  a  fugitive  rise,  and  a  feeble  one.  But  if 
the  needle  goes  into  the  corpora  striata  or  tuber  cinereum  there  is  a 
quite  permanent  and  considerable  elevation  of  temperature.  To  as- 
sume that  a  different  kind  of  thermogenic  center  exists  in  the  pons  is 
begging  the  question. 


ANIMAL  HEAT. 


449 


In  April,  1884,  I  was  the  first  to  make  a  transverse  section  of 
the  corpora  striata  in  the  cat,  which  was  followed  by  the  temperature 
rising  to  llOYo"  F.  Afterward  Drs.  Sachs  and  Aronsohn  more 
exactly  localized  the  center  in  the  caudate  nucleus.  I  also  located 
another  thermogenic  center  in  the  optic  thalami,  a  bilateral  puncture 
of  their  anterior  ends  causing  a  rapid  rise  of  temperature  to  109°  F. 
Von  Tangl,  of  Budapest,  has  confirmed  this  fact  by  experiment  upon 
the  brain  of  a  horse.  Upon  more  exact  localization  this  thalamic 
thermogenic  center  was  found  to  be  located  in  the  tuber  cinereum. 
Hence  the  conclusion  that  the  thermogenic  centers  are  located  in  the 
corpus  striatum  and  tuber  cinereum. 


Fig.  184. — Lesions  of  Cortex  in  Man,  Causing  Elevations  of  Temperature. 

Experiments  by  Ott  show  that  an  increased  supply  of  oxygen  is 
not  necessary  to  a  rise  of  temperature.  A  great  increase  of  arterial 
tension  can  not  elevate  the  temperature  over  1.5°  F.,  as  has  been 
shown  by  Ott  and  Scott. 

The  tuber  cinereum  is  also  connected  with  the  vasomotor  appa- 
ratus. In  experiments  to  find  vasotonic  centers  in  the  thalami  I 
have  located  them  in  their  anterior  part.  Later  experiments  have 
led  to  more  exact  data.  After  puncture  of  the  tuber  with  a  fine 
probe  a  gradual  fall  of  arterial  tension  ensued.  In  about  forty 
minutes  it  amounted  to  one-fourth  the  absolute  pressure.  This  fall 
invariably  ensued  in  six  experiments;  so  that  there  seemed  little 
doubt  that  vasotonic  centers  exist  in  the  thahmii. 

Theemo-inhibitory  Centehs. — Eulenberg  and  Landois  discov- 
ered about  the  cruciate  sulcus  a  center  whose  ablation  was  followed 
by  an  increase  of  temperature.     Prof.  H.  C.  Wood  has  shown  that 

29 


450 


PHYSIOLOGY. 


the  increase  is  due  to  augmented  production  of  heat.  I  have  also 
shown  in  the  cat  that  at  the  juncture  of  the  suprasylvian  and  pust- 
sylvian  fissures  is  another  center  whose  removal  is  followed  by  an 
increase  of  temperature.     This  has  been  confirmed  by  White. 

The  increased  heat-production  after  injury  to  the  Sylvian  and 
cruciate  centers,  the  fall  to  normal,  and  the  subsequent  rise  in  some 
cases  indicate  that  there  is  a  conflict  between  these  centers  and  those 
that  lie  beneath  in  an  effort  to  gain  the  mastery.  This  state  of 
things  is  seen  in  the  temperature  of  patients  -afflicted  with  fever. 

Puncture,  like  fever  poison,  excites  the  thermogenic  centers. 
Antipyretics  act  as  sedatives  to  them  and  so  reduce  their  excitability. 

Albumoses,  peptones,  skatol,  guanine,  and  neurin  have  been  shown 
by  Ott  to  produce  fever. 


ISttAP. 


Fig.  185. — Curves  of  Temperature  and  Respiration  when  Cortex  is 
Removed  and  the  Animal  is  Artificially  Heated. 

Dr.  W.  Hale  White  reports  a  case  in  which  a  bullet  from  a  pistol 
caused  an  injury  of  the  anterior  extremity  of  the  middle  lobe  of  the 
right  hemisphere  and  also  the  third  frontal  convolution,  which  was 
followed  by  a  temperature  of  104.4°  F.  in  less  than  twelve  hours 
after  the  accident. 

Dr.  Page  also  reported  a  case  of  depressed  fracture  of  the  skull 
which  was  about  the  posterior  part  of  the  temporo-sphenoidal  lobe 
and  which  was  followed  by  a  temperature  of  105°  F.  This  tempera- 
ture fell  after  trephining,  and  it  did  not  rise  again.  Fig.  184  shows 
the  position  of  these  lesions  in  man,  and  they  correspond  roughly 
to  the  position  of  the  cruciate  and  Sylvian  centers  in  the  cat. 

Thermolytic    Centers. — These    centers    include   the    cooling 


ANIMAL  HEAT. 


451 


apparatus  of  the  body:  the  polypnceic,  the  sudorific  ,and  the  vaso- 
motor centers. 

Polypnaa. — Professor  Eichet  found  that  with  the  elevation  of 
the  body-heat  of  an  animal  its  respirations  suddenly  increased  to 
350  or  400  per  minute.  This  form  of  respiration  he  termed  polyp- 
noea.  It  was  found  that  the  animal  did  not  do  this  from  want  of 
oxygen.  An  animal  pants  to  cool  himself,  while  a  man  perspires 
for  the  same  purpose.  The  role  of  poiypnoea  is  exclusively  to  reg- 
ulate the  temperature  of  the  body. 

I  have  made  numerous  experiments  to  determine  the  exact  seat 
of  the  polypnceic  center.  To  establish  a  center  three  things  are 
necessary :   (1)  that  its  abolition  causes  the  phenomena  to  disappear. 


JU^flU 


Itoyu 


Fig.  186. — Curve  of  Temperature  and  Respiration  when  the  Tuber 
Cinereum  is  Destroyed  and  the  Animal  is  Artificially  Heated. 

(2)  that  irritation — mechanical,  chemical,  or  electrical — causes  the 
phenomena  to  be  present,  and  (3)  that  the  part  of  the  nervous  sys- 
tem exhibiting  these  peculiarities  be  circumscribed  in  extent.  After 
numerous  observations  and  experiments  it  was  found  that  pressure 
upon  the  tuber  cinereum  with  a  pledget  of  cotton,  or  even  slight 
puncture,  increased  the  normal  respirations  to  the  point  of  poiypnoea. 
Complete  puncture  in  a  normal  animal  was  followed  by  a  rise  to 
106°  F.  within  two  hours,  even  though  the  animal  was  bound  down 
and  had  been  subjected  to  considerable  shock. 

If  now  the  animal  whose  tuber  is  punctured  be  heated,  there 
will  result  no  poiypnoea,  even  though  a  temperature  of  107°  F.  be 
reached.    I  am  convinced  that  the  fnher  cinereum  is  a  center  of  polyp- 


452  PHYSIOLOGY. 

ncea  and  thermotaxis.  When  heat  is  thrown  on  the  body  the  polyp- 
nccic  center  telegraphs  the  respiratory  center  to  work  more  rapidly 
to  throw  off  more  moisture  by  the  expired  air. 

The  afferent  nerves  of  the  thermotaxic  apparatus  are  probably 
those  nerves  in  the  skin  administering  to  the  "hot"  and  "cold"  spots. 

Regulation  of  Loss  of  Heat,  or  Thermolysis. — Heat  is  lost  by  an 
animal  in  various  ways.  It  may  be  by  direct  radiation  and  conduc- 
tion from  the  skin,  by  the  extraction  of  heat  during  the  process  of 
evaporating  perspiration,  by  warming  the  respired  air,  and  by  the 
discharge  of  urine  and  faeces. 

Skin  Eadiation  and  Conduction. — The  skin  is  the  main  means 
of  escape  of  the  bodily  heat.  Nearly  three-fourths  of  the  heat  which 
escapes  from  the  economy  does  so  through  the  skin  as  a  means. 

A  marked  difference  between  the  temperature  of  the  skin  and 
that  of  the  surrounding  atmosphere  constitutes  a  prime  factor  in 
radiation.  When  the  enveloping  medium  is  very  cold  radiation  from 
the  skin's  surface  is  very  rapid. 

The  cutaneous  circulation  has  considerable  to  do  with  the  dissi- 
pation of  heat.  The  caliber  of  the  peripheral  vessels  is  governed  by 
the  vasomotor  system,  which  is  itself  under  the  guidance  of  the  cen- 
tral nervous  system. 

External  heat  refiexly  causes  dilatation  of  the  cutaneous  vessels, 
so  that  at  such  times  the  skin  becomes  red  and  engorged.  It  con- 
tains more  fluids  and  thus  is  a  better  conductor  of  heat.  More  blood 
being  at  the  body  surface  allows  of  greater  and  more  rapid  loss 
through  radiation. 

External  cold  refiexly  causes  a  contraction  of  the  peripheral  ves- 
sels; so  that  their  lumina  are  narrowed.  In  consequence  there  is 
less  blood  circulating  in  the  skin,  which  appears  pale  and  contains 
less  fluid;   so  that  the  radiation  of  heat  is  markedly  hindered. 

By  reason  of  nervous  stimulation  the  sweat-glands  are  at  times 
made  to  functionate  very  freely;  whereupon  the  skin's  surface  be- 
comes bathed  in  a  sensible  perspiration.  For  the  conversion  of  this 
moisture  into  vapor  heat  is  necessary.  It  is  by  the  abstraction  of 
this  heat  from  the  underlying  tissues  that  the  body  owes  much  of 
its  loss  when  its  parts  are  hyperpyrexial.  One  pound  of  water  in 
evaporating  takes  up  1047  B.  H.  U.  daily. 

The  covering  of  the  body  by  clothing  during  various  seasons  of 
the  year  contributes  much  to  the  proper  regulation  of  loss  of  heat, 
so  that  the  mean  temperature  may  be  maintained  fairly  constant. 

Fever. — The  process  of  fever  is  one  of  absorbing  interest  dur- 


ANBIAL  HEAT. 


453 


DAY  AFTER.. 
CHIL]- 


PERIODS.  1 


Fig.    187. — Heat   Production   and   Heat   Dissipation   in   Man   during   a 
Parox\'sm  of  Malarial  Fever— a  Great  Increase  of  Heat  Production. 


454  PHYSIOLOGY. 

ing  every  period  of  a  physician's  life.  The  constant  level  of  tem- 
perature in  man  is  accounted  for  by  two  theories:  One  that  it  is 
due  to  changes  in  heat-i^roduction ;  the  otlier,  held  by  a  minority, 
that  it  is  kept  so  by  changes  in  heat-dissipation  under  the  varying 
conditions  of  external  temperature. 

In  a  case  of  fever  generated  by  the  malarial  parasite  I  found 
with  the  human  calorimeter  an  increased  production  of  heat  as  the 
primary  cause  of  the  fever.  In  the  case  of  fever  generated  by  the 
subcutaneous  injection  of  putrid  blood  I  found  a  fever  caused  by  an 
increased  production  of  heat  in  the  animal. 

As  a  rule,  it  is  true  that  fever  is  set  up  by  an  increase  of  heat- 
production  beyond  that  of  heat-dissipation.  But  when  this  is  once 
established  the  fever  continues,  not  from  an  excessive  production, 
but  from  an  altered  relation  between  heat-production  and  heat- 
dissipation. 

That  the  basal  thermogenic  centers,  the  corpus  striatum  and 
tuber  cinereum,  play  a  prominent  part  in  the  production  of  fever  is 
proved  by  the  fact  that  putrid  blood  and  betatetrahydronaphthylamin 
both  produce  a  rise  of  temperature.  They  are  powerless  after  a  sec- 
tion behind  the  tuber  cinereum  to  elevate  the  temperature. 

Antipyrin  reduces  the  temperature  by  an  action  upon  the  cor- 
pora striata. 

Experiments  in  my  laboratory  by  Dr.  W.  S.  Carter  proved  that 
whilst  the  temperature  of  the  body  has  a  rhythm,  there  was  no 
rhythm  in  either  heat-production  or  heat-dissipation. 

All  recent  researches  go  to  show  that  fever  is  not  a  fire  that  is 
continuously  kept  up  by  an  excessive  oxidation  of  the  constituents 
of  the  human  body.  For  instance,  if  the  amount  of  water  flowing 
into  a  vessel  partly  filled  with  water  is  equal  to  2,  and  the  amount 
going  out  is  equal  to  2,  the  level  of  the  water  will  be  the  same.  But 
if  the  amount  of  water  going  into  the  vessel  is  equal  to  3  and  the 
amount  going  out  equal  to  2,  the  level  of  the  water  will  rise.  If, 
however,  the  amount  going  into  the  vessel  should  suddenly  fall  to  1 
and  the  amount  going  out  should  do  the  same,  the  level  of  the  water 
would  be  nearly  the  same  as  before.  If,  now,  you  substitute  for  the 
amount  of  water  going  in  the  amount  of  heat  produced,  and  for  the 
water  going  out  the  amount  of  heat  dissipated,  and  the  level  of  the 
water  as  the  height  of  temperature,  it  is  easy  to  see  how  a  dimin- 
ished production  and  dissipation  of  heat  due  to  want  of  food  and  the 
waste  of  the  body  by  the  fever  process,  may  still  keep  up  a  high 


ANIMAL  HEAT.  455 

fever,  although  both  are  dhninished  below  what  is  generated  and 
dissipated  in  a  state  of  health. 

The  physico-chemical  cause  of  death  in  fever  by  hyperpyrexia 
is  due  to  a  coagulation  of  cell-globulin.  If  heated  long  enough,  a 
temperature  of  42°  C.  will  coagulate  it. 

Postmortem  Temperature. — Usually  after  death  the  body  cools 
gradually,  depending  upon  the  temperature  of  the  external  atmos- 
phere and  the  body-surface.  The  body  of  a  child  or  emaciated  sub- 
ject cools  more  rapidly  than  does  that  of  a  well-developed  and  well- 
nourished  adult  body. 

A  temporary  increase  of  postmortem  temperature  is  due  to  the 
change  of  myosinogen  into  myosin  and  to  those  series  of  cliemical 
changes  immediately  succeeding  death. 

When  death  has  occurred  from  tetanus,  acute  rheumatism., 
typhoid,  small-pox,  cholera,  or  injuries  to  the  brain,  there  is  noxo'I 
a  marked  postmortem  rise  in  temperature. 


CHAPTER  XI. 

THE   MUSCLES. 

Covering  np  the  l^ones  and  attached  to  their  surfaces  at  certain 
definite  places  is  the  soft,  red,  fleshy  portion  of  the  body:  the  mus- 
cular substance.  This  consists  of  not  one  homogeneous  environing 
mass,  but  of  a  great  number  of  distinct  fleshy  masses,  called  muscles. 
These  are  of  various  forms  and  sizes;  number  about  four  hundred; 
and  are,  for  the  most  part,  arranged  in  pairs.  It  is  mainly  to  the 
shape  and  disposition  of  these  muscles  that  the  body  owes  the  regu- 
larity of  its  contour. 

It  is  by  the  power  of  these  skeletal  muscles  that  the  animal  is 
able  to  move  about,  procure  means  of  sustenance,  care  for  its  young, 
etc. ;  but  it  must  be  borne  in  mind  that  muscles — not  so  powerful  as 
are  the  skeletal  muscles,  but  muscles,  nevertheless — are  contained 
within  the  viscera  and  blood-vessel  walls.  These  muscles  have  very 
important  functions  to  perform  in  aiding  tlie  processes  of  metab- 
olism :  that  balance  which  when  disturbed  produces,  not  health,  but 
disease. 

Any  animal  motion  means  muscle.  Muscular  tissue  is  empowered 
with  contractility;  that  is,  an  ability  to  shorten  itself  when  acted  upon 
by  any  stimulus.  By  its  shortening  it  produces  movement  to  parts  to 
which  one  or  both  of  its  ends  are  attached.  The  resultant  motions 
may  be  the  very  common  ones  of  walking,  running,  various  manual 
employment,  etc.,  or  the  peristaltic  movements  of  .stomach  and  in- 
testines, or  the  variations  in  the  sizes  of  the  lumen  of  the  blood- 
vessels. Any  animal  movement  should  at  once  recall  to  the  mind  of 
the  student  that  it  is  the  resultant  of  some  muscular  contractility 
produced  by  the  influence  of  a  stimulus  to  it,  whether  that  be  nerv- 
ous, electrical,  mechanical,  or  thermal. 

Muscular  tissue  consists  of  fibers  bound  together  into  those  dis- 
tinct organs  already  mentioned  as  muscles,  and  in  this  condition  is 
known  as  the  meat  of  animals. 

In  the  f.ne  anatomy  of  the  muscles  I  have  followed  the  writings 
of  Professor  Shaefer,  as  they  appear  in  Quain's  "Anatomy,"  of  which 
this  is  an  abstract. 

Varieties. — When  seen  under  the  microscope,  these  fibers'  are 
found  to  be  cross-striped,  or  striated;  as  many  of  them  are  under  the 
control  of  the  will,  they  are  usually  spoken  of  as  being  voluntary. 
(456) 


THE  MUSCLES.  457 

In  the  coats  of  the  blood-vessels  and  in  the  hollow  .viscera  is 
another  variety  of  muscular  fibers,  often  making  a  distinct  layer  or 
layers  to  these  organs.  In  this  kind  the  libers  do  not  have  the  cross- 
striped  appearance,  but  are  plain,  or  unstriped.  Nearly  all  of  these 
are  not  under  the  control  of  the  will,  and  are,  hence,  involuntary.  It 
must  here  be  noted,  however,  that  the  muscle  of  the  heart — which, 
as  everyone  knows,  is  an  involuntary  muscle — is  exceptional  to  this 
class  of  muscle  in  that  its  fibers  are  very  plainly  cross-striped.  jSTever- 
theless,  it  presents  differences  from  the  striped  fibers  of  skeletal 
muscles;  so  that  it  has  become  customary  with  very  many  authors 
to  class  it  under  the  separate  title  cardiac  muscular  tissue. 

The  muscular  fibers  of  the  skeleton  are  generally  collected  into 
distinct  organs  of  various  sizes  and  shapes  which  have  at  each  end 
a  tendon  by  which  they  are  attached  to  the  skeleton. 

The  fibers  of  the  muscles  are  collected  together  into  bundles, 
called  fasciculi.  In  the  fasciculi  the  fibers  are  parallel,  so  that  the 
fasciculi  wind  from  one  tendinous  end  to  the  other,  except  in  a  few 
muscles  like  the  rectus  abdominis.  In  this  instance  the  body  of 
the  muscle  is  interrupted  by  interposed  tendinous  tissue.  The  fas- 
ciculi themselves  do  not  mingle  with  one  another  and,  for  the  most 
part,  run  parallel,  although  in  many  cases  they  converge  to  their 
tendinous  endings. 

The  covering  of  the  entire  muscle  is  termed  the  epimysitwi,  and 
is  a  connective-tissue  envelope.  The  covering  of  areolar  tissue  which 
insheathes  the  fasciculi  of  the  muscle  is  spoken  of  as  the  perimysium. 
The  latter,  a  septum  from  the  epimysium.  furnishes  to  each  fascicu- 
lus a  special  covering  as  well  as  furnishing  it  with  blood-vessels  and 
nerves.  Within  each  compartment  lie  a  number  of  muscle-fibers 
which  are  usually  parallel  to  one  another  and  held  together  by  a  very 
delicate  reticular  connective  tissue.  This  areolar  network  is  called 
the  endomysium,  but  does  not  make  a  continuous  covering  and  so 
cannot  be  said  to  form  sheaths  for  them.  Each  fiber  of  the  muscle, 
however,  has  a  tubular  sheath,  but  this  sheath  is  not  composed  of  the 
areolar  tissue  just  mentioned.  The  special  function  of  the  areolar 
tissue  seems  to  be  to  connect  the  fasciculi  and  fibers,  and  to  support 
and  conduct  the  blood-vessels  and  nerves  in  their  ramifications  be- 
tween the  various  parts. 

Fasciculi  in  form  are  prismatic,  so  that  a  transverse  section 
shows  an  angular  outline.  The  thickness  of  a  fasciculus,  as  well  as 
the  number  of  fibers  of  which  it  is  composed,  varies.  The  texture  of 
a  muscle,  whether  coarse  or  fine,  depends  upon  the  large  or  small 


458  PHYSIOLOGY. 

fasciculi  contained  within  it;  thus,  the  glutei  are  coarse,  the  muscles 
of  the  eye  fine. 

The  length  of  the  fasciculi  is  not  always  the  same  as  the  length 
of  the  muscle;  this  characteristic  depends  upon  the  arrangement  of 
the  tendons  to  wliieli  the  muscle  is  attached.  When  the  tendons  are 
attached  to  the  ends  of  a  long  muscle,  as  the  sartorius,  the  fasciculi 
run  from  one  end  of  the  muscle  to  the  other  and  so  are  of  consid- 
erable length.  However,  a  long  muscle  may  be  made  up  of  a  series 
of  short  fasciculi  attached  obliquely  to  one  another  by  beveled  ends. 
Short  fasciculi  thus  attached,  as  in  the  rectus  muscle  of  the  thigh, 
have  stronger  action  than  where  they  run  the  extent  of  the  nmscle. 

Fibers. — The  form  of  the  muscle-fibers  is  cylindrical  or  prism- 
atic with  rounded  angles.  Their  diameter  varies  very  considerably, 
even  in  each  muscle,  although  a  certain  standard  is  found  to  exist  in 
every  muscle.  The  largest  human  fibers  average  one-tenth  of  an  inch 
in  diameter,  and  fiom  that  size  to  one  two-hundred-and-fiftieth  of  an 
inch  fibers  may  l)e  found.  Between  the  size  of  the  muscle  and  that 
of  its  fibers  there  is  no  constant  relation. 

The  length  of  the  muscular  filjers  does  not  generally  exceed  one 
and  one-half  inches.  Thus,  in  a  long  fasciculus,  the  fibers  do  not 
reach  its  whole  length,  but  end  in  a  rounded  or  tapering  end  invested 
with  sarcolerama  and  cohering  with  neighboring  fibers.  There  is,  as 
a  rule,  no  anastomosis  or  division  of  the  fibers  of  a  muscle,  except  in 
the  tongue  of  a  frog,  where  they  branch  beneath  the  mucous  mem- 
brane to  which  they  are  attached.  The  same  thing  has  been  observed 
in  the  tongue  of  man. 

Sarcole:mma. — The  sarcolemma  is  a  tubular  sheath  inclosing  the 
soft  substance  of  the  muscle.  It  is  an  elastic,  transparent,  homoge- 
neous memljrane ;  it  is  rather  tough  and  can  remain  intact  even 
though  the  muscle  be  ruptured.  Upon  its  inner  side  are  found  nuclei 
which,  however,  belong  to  the  muscle  rather  than  to  the  inclosing 
membrane. 

Structure. — With  a  low  magnifying  power,  the  muscle  presents 
clear  pellucid  fibers  which  are  cross-striped  with  bands  alternately 
dark  and  light.  That  this  striation  is  not  on  the  surface  alone,  but 
extends  throughout  the  substance  of  the  muscle,  is  readily  demon- 
strated by  altering  the  focus  of  the  microscope.  The  stripes  do  not 
occur  on  the  sarcolemma,  but  throughout  the  sarcous  substance  in- 
closed by  the  former. 

The  breadth  of  the  bands  is  about  ^/i7ooo  inch,  so  that  eight  or 
nine  dark  bands  may  be  counted  in  Viooo  inch.     While  this  is  the 


THE  MUSCLES. 


459 


1.  Diagram  of  part  of  a  striped  muscular  fiber.  8,  Sarcolemma.  Q, 
Transverse  stripes.  F,  FibrillEe.  K,  Muscle  nuclei.  N,  Nerve-fibers  entering 
it  with  A,  its  axis  cylinder,  and  Kiihnes  motorial  end-plate,  E,  seen  in  profile. 

2.  Transverse  section  of  part  of  a  muscular  fiber,  showing  Cohnheim's 
areas,   C. 

3.  Isolated  muscular  fibrillae. 

4.  Part  of  an  insect's  muscle,  greatly  magnified.  A,  Krause-Amici's  line 
limiting  the  muscular  cases.  B,  The  doubly  refractive  substance.  C,  Hensen's 
disc.     D,   Singly  refractive  substance. 

5.  Fibers  cleaving  transversely  into  discs. 

6.  Muscular  fiber  from  the  heart  of  a  frog. 

7.  Development  of  a  striped  muscle  from  a  human  foetus  at  the  third 
month. 

8.  9.  Muscular  fibers  of  the  heart.  C,  Capillaries.  B,  Connective  tissue 
corpuscles. 

10.  Smooth  muscular  fibers. 

11.  Transverse  section  of  smooth  muscular  fibers. 

12.  Muscular  fibers  with  tendon. 

13.  Interfibrillary  muscular  nerves. 


460  PHYSIOLOGY. 

common  breadth  in  human  muscle,  yet  they  arc  much  narrower  in 
different  parts;  s6  that  there  may  be  twice  as  many  bands  existing 
in  the  space  just  mentioned.  This  striation  is  found  in  all  muscles 
attached  to  the  skeleton,  in  the  heart,  pharynx,  upper  oesophagus, 
diaphragm,  urethral  sphincter,  external  anal  sphincter,  as  well  as 
in  the  muscles  of  the  middle  ear. 

When  a  muscle  is  deeply  focused,  the  appearance  of  the  striae 
is  somewhat  altered;  a  finely  dotted  line  is  seen  to  pass  across  the 
middle  of  each  light  band.  This  is  supposed  to  represent  Krause's 
memhrane  stretching  across  the  fiber  and  attached  to  the  surface  of 
the  sarcolemma.  However,  there  is  reason  to  believe  that  the  ap- 
pearance of  a  dotted  line  in  this  position  in  the  fresh  fiber  is  due  to 
tlie  peculiar  optical  condition  of  the  tissue. 

A  fine,  clear  line  is  sometimes  seen  in  the  middle  of  each  dark 
band,  and  is  known  as  the  line,  or  disc  of  Hensen. 

Since  there  seems  to  be  such  variance  as  to  muscle-structure  and 
so  many  different  names  are  met  with  in  text-books,  it  might  be  well 
to  call  the  student's  attention  to  the  fact  that  Dobie's  line,  Amici's 
line,  and  Krause's  membrane  are  terms  used  to  describe  the  same 
condition.  They  designate  the  dark  line  bisecting  the  white  band. 
Hensen's  band  occurs  in  the  dark  bands. 

In  addition  to  the  cross-striping,  the  fiber  of  the  muscle  has 
longitudinal  striation.  When  a  muscle  has  been  very  carefully  teased 
with  fine  needles  after  having  been  previously  hardened  in  spirits, 
an  interesting  result  follows.  The  muscle-fibers  break  up  into  fine, 
longitudinal  elements  of  a  rounded  or  angular  section  which  run  from 
end  to  end  of  the  fiber.  These  have  been  very  aptly  termed  muscle- 
columns,  or  sarcostyles. 

Each  sarcostyle  appears  to  consist  of  a  row  of  elongated  pris- 
matic particles  with  clear  intervals.  These  particles  are  termed 
sarcous  eleinents.  The  sarcostyles  in  some  muscles  are  striated  longi- 
tudinally. This  appearance  has  led  some  authors  to  believe  that  they 
are  composed  of  still  finer  elements,  or  fibrils. 

Under  some  conditions,  the  fibers  show  a  tendency  to  cleave 
across  in  a  direction  parallel  to  the  bands,  and  even  to  break  up  into 
transverse  plates,  or  discs.  The  latter  are  made  up  by  the  lateral 
cohesion  of  the  sarcous  elements  of  adjacent  sarcostyles.  To  the  for- 
mation of  such  discs,  therefore,  every  sarcostyle  furnishes  a  particle, 
which  coheres  with  its  neighbors  on  each  side,  and  this  with  perfect 
regularity. 

Sarcoplasm  is  the  intercolumnar  substance  by  which  the  sarco- 


THE  MUSCLES.  461 

styles  are  united  into  the  muscle-fibers.  It  is  the  protoplasm  of  the 
muscle-corpuscles,  and  forms  a  fine  network  throughout  the  whole 
muscular  fiber. 

From  an  examination  of  the  aforementioned  facts,  Bowman  was 
induced  to  believe  that  the  division  of  the  fiber  into  fibrils,  or  sarco- 
stj^les,  was  merely  a  phenomenon  of  the  same  kind  as  the  separation 
into  discs,  only  a  more  common  occurrence. 

CoHNHEiM''s  Areas. — If  a  transverse  section  be  made  of  a  mus- 
cular fiber,  or  the  surface  of  a  separated  disc  be  examined  with  a 
strong  objective,  there  appear  in  the  field  small  polygonal  areas 
separated  by  fine  lines.  In  acid  preparations  they  give  the  appear- 
ance of  a  network.  These  areas  represent  sections  of  the  muscle- 
columns,  and  are  usually  designated  as  Cohnlieim's  areas.  The  line 
between  them  represents  the  sarcoplasm,  or  intercolumnar  substance. 

When  a  muscle-fiber  placed  in  fresh  serum  is  examined,  fine, 
longitudinal  lines  are  seen  running  through  the  cross-striping.  If, 
now,  a  weak  acid  is  added  to  swell  the  muscular  substance  and  render 
it  more  transparent,  these  lines  can  be  traced  from  end  to  end  of  the 
fiber.  By  careful  management  of  the  microscope,  it  is  found  that 
these  lines  are  really  the  optical  section  of  the  planes  of  separation 
between  the  sarcostyles ;  that  is  to  say,  the  optical  effect  of  the  sarco- 
plasm, or  intercolumnar  substance.  The  sarcoplasm,  in  transverse 
section,  presents  the  aspect  of  network;  in  longitudinal  optical  sec- 
tion it  has  the  appearance  of  fine,  parallel  lines.  The  student  can 
very  readily  imagine  how  these  effects  can  he  produced  by  the  pres- 
ence of  a  small  amount  of  interstitial  substance  lying  between  closely 
packed  prismatic  columns. 

In  most  muscular  fibers  the  sarcoplasm  exhibits  a  peculiarity  of 
arrangement  which  has  a  very  characteristic  influence  upon  the  op- 
tical appearance  of  the  fiber.  In  a  longitudinal  view  of  fresh  muscle, 
the  lines  representing  intercolumnar  sarcoplasm  present  at  regular 
intervals  along  their  course  rather  marked  enlargements.  These  en- 
largements lie  in  the  bright  cross-strige,  either  in  their  middle  or  near 
their  junction  with  the  dim  cross-stripes.  These  sarcoplasm  nodules 
have  the  appearance  of  dots  upon  fine  longitudinal  lines  which  run 
through  the  muscle;  in  the  more  extended  fibers  these  dots  are  in 
double  rows.  In  less  extended  parts  they  are  thicker  and  blend 
together  in  the  middle  of  the  liright  stri-p. 

Structure  of  the  Wing-muscles  of  Insects. — The  study  of  these 
muscles  has  furnished  the  key  to  the  comprehension  of  the  intimate 


462  PHYSIOLOGY. 

structure  of  muscle.  As  to  their  structure,  the  wing-fibers  are  in 
complete  agreement  with  ordinary  muscles.. 

Wing-fibers  occur  in  large  bundles  of  muscle-columns  or  sarco- 
styles  imbedded  in  considerable  amount  of  granular  sarcoplasm, 
while  the  whole  of  the  structure  is  inclosed  within  a  sarcolemma. 
The  nuclei  are  scattered  here  and  there.  The  quantity  of  sarco- 
plasm in  wing-muscle  is  relatively  far  greater  than  in  the  ordinary 
muscle. 

When  wing-muscle  has  been  carefully  teased  into  muscle-col- 
umns, or  sarcostylcs,  it  is  found  that  they  contract  while  the  sarco- 
plasm is  quiescent.  The  muscle-columns  can  then  be  very  carefully 
studied,  when  they  show,  like  other  muscles,  the  alternate  bright  and 
dark  cross-striping.  Each  bright  stria  is  bisected  by  a  line  which  is 
the  optical  section  of  a  transverse  membrane:  the  membrane  of 
Krause.  These  membranes  divide  the  fibers  into  a  series  of  seg- 
ments, called  sarcomeres. 

In  a  muscle  hardened  by  spirits  each  sarcomere  is  seen  to  con- 
tain: (1)  in  its  middle,  a  strongly  refracting,  disclike  sarcous  ele- 
ment; (3)  at  either  end  (next  the  membrane  of  Krause)  a  clear 
interval  occupied  by  hyaline  substance.  With  strong  lenses  the 
sarcous  elements  can  be  made  out  to  be  composed  of  a  sarcous  sub- 
stance which  stains  with  logwood ;  it  is  pierced  by  short,  tubular 
canals  which  extend  from  the  clear  interval  as  far  as  the  middle  of 
the  disc.  It  is  these  canals  which  give  to  the  sarcous  element  its 
longitudinal  striping. 

If,  for  any  reason,  the  sarcostyle  becomes  extended,  the  sarcous 
elements  tend  to  separate  into  two  parts  with  an  interval  between 
them ;  vice  versa,  if  the  muscle  be  contracted  or  retracted  the  sarcous 
elements  tend  to  encroach  upon  the  clear  intervals.  At  the  same 
time  the  sarcous  elements  become  swollen,  so  that  the  sarcomeres 
are  bulged  out  at  their  middle  and  contracted  at  their  ends. 

Changes  in  Contraction. — When  these  muscles  contract,  the  sar- 
cous elements  become  bulged  out  and  shortened,  while  the  fluid  of 
the  clear  interval  becomes  relatively  diminished  in  amount.  The 
ends  of  the  sarcomeres  are  thereby  contracted  opposite  the  membrane 
of  Krause,  so  that  the  sarcostyles  become  moniliform.  This  altera- 
tion in  the  shape  of  the  sarcostyle  necessarily  affects  the  sarcoplasm 
which  lies  in  their  interstices.  It  must  become  squeezed  out  of  the 
parts  which  are  opposite  the  bulgings  of  the  sarcostyles  and  into 
those  parts  which  are  opposite  their  constrictions.  In  other  words, 
the  sarcoplasm  must  accumulate  in  greater  quantity  opposite  the 


THE  MUSCLES.  463 

clear  bands  and  the  membranes  of  Krause,  and  must  necessarily 
diminirili  in  amount  opposite  the  sarcous  elements. 

In  the  living  muscle  this  change  in  the  position  of  the  sarco- 
plasm  during  contraction  can  be  observed;  the  muscle-columns  tend 
to  cause  the  contracted  parts  to  appear  dark,  the  bulged  parts  bright, 
in  comparison. 

Appearance  of  Muscle  under  Polarized  Light. — Briicke  was  the 
first  to  point  out  that  the  fiber  is  not  composed  entirely  of  a  double 
refracting,  or  anisotropous,  substance.  In  addition  there  is  a  cer- 
tain amount  of  singly  refracting,  or  isotropous,  material.  This 
investigator  points  out  that  there  is  a  difference  between  the  appear- 
ances presented  by  living  muscle  examined  in  its  own  plasma  and 
those  of  dead  and  hardened  muscle  examined  in  glycerin.  In  living 
muscle  nearly  the  entire  fiber  is  doubly  refracting,  the  isotropous 
substance  occurring  only  as  fine  transverse  lines  or  as  rows  of  rhom- 
boidal  dots  which  are  united  to  one  another  across  the  anisotropous 
substance  by  fine  longitudinal  lines.  Sarcous  element  is  anisotropic ; 
sarcoplasm  is  isotropic. 

Nuclei. — In  muscles  that  are  cross-striped  are  found  a  number 
of  clear,  oval  nuclei.  They  are  sometimes  spoken  of  as  muscle-cor- 
puscles. In  mammalian  muscle  they  usually  lie  upon  the  inner  sur- 
I'ace  of  the  sarcolemma.  In  the  muscles  of  the  frog  and  reptiles  the 
nuclei  lie  in  the  substance  of  the  fiber  surrounded  by  a  small  amount 
of  protoplasm.  When  the  nuclei  lie  immediately  beneath  the  sarco- 
lemma they  are  more  or  less  flattened.  Each  nucleus  contains  one 
or  two  nucleoli.  Mitotic  figures,  denoting  division  of  the  nuclei, 
have  been  observed.  The  nuclei  are  not  very  readily  seen  in  fresh 
muscle,  due  to  their  being  of  the  same  refractive  index  as  the  sar- 
cous substance.  Only  after  they  have  undergone  some  spontaneous 
change  or  acetic  acid  has  been  added  to  the  specimen  can  they  be 
readily  discerned. 

In  the  rabbit  and  rays  of  fishes  some  of  the  voluntary  muscles 
present  differences  from  others,  both  as  to  appearance  and  mode  of 
action.  Thus,  while  most  of  the  voluntary  muscles  are  pale  and  con- 
tract forcibly  when  irritated,  the  soleus  and  semitendinosus  show 
different  characteristics.  They  are  of  a  deeper  color  and  respond 
'with  slow,  prolonged  contractions  when  stimulated.  Thus,  in  these 
animals  there  are  red  and  white  muscles. 

In  other  animals,  this  distinction  of  muscles  is  not  found  as 
regards  a  whole  muscle,  but  may  affect  individual  fibers.  Thus,  in 
the  diaphragm  many  of  the  fibers  have  numerous  nuclei  imbedded 


464  PHYSIOLOGY. 

within  the  protoplasm  so  as  to  form  an  almost  continuous  layer 
beneath  the  sarcoleimna. 

Relation  to  Tendons. — When  a  muscle  terminates  in  a  tendon,  it 
is  found  that  the  muscular  fibers  cither  run  in  the  same  direction  as 
the  fibers  of  the  tendon  or  Join  with  the  tendon  at  an  acute  angle. 
According  to  Toldt,  the  delicate  connective-tissue  elements  covering 
the  several  muscular  fibers  pass  from  the  latter  directly  into  the  con- 
nective-tissue elements  of  the  tendon.  According  to  another  author, 
the  ends  of  the  muscular  fibers  are  believed  to  be  fastened  to  the 
smooth  tendons  by  means  of  a  special  cement.  However,  it  is  prob- 
able that  the  areolar  tissue  which  lies  between  the  tendon-fibers 
passes  between  the  ends  of  the  muscular  fibers  to  be  gradually  lost 
in  the  interstitial  connective-tissue. 

Blood-vessels  of  Muscle. — The  blood-vessels  to  the  muscles  are 
very  numerous.  The  average  muscle  leads  such  an  active  life  that 
its  nourishment  and  repair  material  must  be  in  proportionate  rela- 
tion. Unlike  the  organs,  as  the  kidney  and  spleen,  which  usually 
are  supplied  by  one  artery  and  vein,  muscles  receive  several  branches 
from  various  arteries  which  pierce  the  muscle  at  difi:erent  points 
along  its  course. 

The  artery  and  vein  usually  are  in  close  proximity,  being  held 
in  position  by  the  connective  tissue  upon  the  perimysium.  The  capil- 
laries lie  between  the  muscle-fibers  in  the  endomysium,  but  outside 
of  the  sarcolemma.  Here  the  capillaries  are  small,  and  form  a  fine 
network  with  narrow,  oblong  meshes,  which  are  stretched  out  in  the 
direction  of  the  fibers.  The  capillaries  have  both  longitudinal  and 
transverse  vessels.  The  lymph  that  is  destined  to  support  the  sar- 
cous  substance  must  pass  through  the  sarcolemma  to  reach  the  same. 

Muscle  Nerve-supply. — The  nerve-supply  to  muscles  is  both 
motor  and  sensory.  Each  muscle-fiber  receives  a  motor  nerve-fiber. 
The  trunJv  of  the  motor  nerve,  as  a  rule,  enters  the  muscle  at  its 
geometrical  center  (Schwalbe) ;  thus,  the  point  of  entrance  in  a  long, 
spindle-shaped  muscle  lies  near  its  middle.  At  this  "geometrical 
center"  there  is  the  point  of  least  disturbance  during  contraction  of 
the  muscle.  After  the  trunk  of  the  nerve  pierces  the  muscle  it  pro- 
ceeds to  divide  dichotomously  until  there  are  just  as  many  nerve- 
fibers  as  muscle-fibers.  A  nerve-fiber  now  enters  each  muscle-fiber, 
to  do  which,  of  course,  it  must  pierce  the  sarcolemma.  The  point 
of  entrance  forms  an  eminence  known  as  Doyere's  eminence,  or 
motorial  end-plate.  At  this  point  the  sheath  of  the  nerve-fiber 
becomes  continuous  with  the  sarcolemma.     The  eminence  itself  con- 


THE  MUSCLES. 


465 


sists  of  a  mass  of  protoplasm  (sarcoplasm)  containing  granules  and 
nuclei.  Beneath  the  sarcolemma  the  original  nerve-fiber  is  broken 
up  into  a  number  of  divisions,  spoken  of  as  nerve-endings.  These 
are  divisions  of  the  axis-cylinder  which  are  spread  over  the  sarcous 
substance  without  piercing  it.  To  this  branched  arrangement  of 
the  nerve-endings  Kiihne  gave  the  name  motor  spray. 


Fig.  189. — Unstriped  Muscular  Tissue.     (Ellenberger.) 

A  and  B,  Foetal  cells.     C,  U,  Fully  formed  fiber.     /,   Bundle  of  fibers. 
K,  Cross-section  of  bundle  of  pale  muscular  fibers. 

The  nerve-endings  are  thus  confined  to  very  small  areas  on  the 
muscle-fibers  which  have  been  termed  by  the  same  author  fields  of 
innervation.  As  a  rule,  each  muscle-fiber  has  but  one  such  area;  it 
is  the  exception  to  find  more  than  one,  but  as  many  as  eight  have 
been  found  in  very  long  fibers. 

Sensory  fibers  are  also  found  in  muscles,  for  it  is  through  their 
presence  that  we  obtain  muscle  sensibility.     They  seem  to  be  dis- 

30 


466  PHYSIOLOGY. 

tributed  upon  the  outer  surface  of  the  sarcolemma,  where  there  is 
formed  a  plexus.     This  plexus  winds  round  the  muscle-fiber. 

Cardiac  Muscle. — Some  mention  has  previously  been  made  con- 
cerning cardiac  muscle,  so  that  at  this  point  only  its  most  striking 
peculiarities  will  be  mentioned,  and  that  cursorily,  (a)  It  is  a 
striped  muscle.  However,  its  striations  are  not  nearly  so  distinctly 
marked  as  are  those  of  voluntary  muscle.  Occasionally  it  is  noticed 
to  be  marked  longitudinally,  (b)  Cardiac  muscle-fibers  possess  no 
sarcolemma.  (c)  Its  fibers  branch  and  anastomose,  (d)  The  nucleus 
is  placed  in  the  center  of  each  cell.  One  author  says  that  cardiac 
muscle  stands,  physiologically,  midway  between  striped  and  unstriped 
muscle.  When  stimulated,  its  contractions  occur  slowly,  but  last  for 
a  considerable  length  of  time. 

Nonstriped  Muscle. — These  muscles  are  made  up  of  a  number  of 
contractile  fiber-cells,  of  an  elongated,  fusiform  shape,  usually 
pointed  at  the  end.  These  fiber-cells  may  be  readily  demonstrated 
by  placing  the  tissue  in  a  strong  alkaline  solution  or  in  a  solution 
of  strong  nitric  acid. 

Upon  transverse  section  they  are  generally  prismatic,  but  some- 
times are  more  flattened.  Their  muscle-substance  is  doubly  refract- 
ing. Each  cell  has  a  nucleus  which  is  either  elongated  or  oval.  It 
may  contain  one  or  more  nucleoli.  The  nucleus  is  brought  into 
view  by  means  of  dilute  acetic  acid  or  staining  reagents. 

The  involuntary  fiber-cells  have  a  delicate  sheath,  which,  like 
the  sarcolemma  of  voluntary  muscle-fiber,  is  very  apt  to  become 
wrinkled  when  the  fiber  is  contracted.  By  reason  of  this  an  indis- 
tinctly striated  appearance  may  be  produced. 

While  fiber-cells  do  occur  singly,  yet  it  is  more  common  for  them 
to  be  found  in  groups.  Thus,  muscular  sheets,  or  bundles,  are  pro- 
duced which  may  cross  one  another  and  interlace,  being  held  in  posi- 
tion by  enveloping  connective  tissue.  The  individual  cells  are  united 
by  the  presence  of  a  very  delicate  cement. 

The  average  length  of  the  fiber-cells  ranges  from  Vioo  to  Voqo 
of  an  inch ;  those  forming  the  middle  coat  of  the  arteries  are  shorter, 
those  in  the  intestinal  tract  and  pregnant  uterus  are  considerably 
longer. 

Where  Found. — The  unstriped  muscular  tissue  is  more  gen- 
erally distributed  within  the  body  than  one  would  suppose.  It  is 
found  in  the  lower  part  of  the  oesophagus,  in  the  stomach,  small  and 
large  intestines;  in  arteries,  veins,  and  lymphatics;  in  the  ureters, 
bladder,  and  urethra ;  in  the  internal  female  generative  organs,  etc. 


THE  MUSCLES.  467 

Blood-supply. — The  blood-supply  to  unstriped  muscle  is  very 
free,  but  not  nearly  so  liberal  as  that  to  voluntary  muscle.  The  nerve- 
supply  is  from  the  sympathetic  system,  and  comprises  both  medullated 
and  nonmedullated  fibers.  The  fibers  form  a  main  plexus,  lying  in 
the  connective  tissue  of  the  perimysium.  From  this  plexus  of  fibers 
there  come  off  numerous  fibrils,  which  traverse  the  fiber  and  nucleus. 

Irritability  of  Muscle. — Contractility,  elasticity,  tonicity,  and 
irritability  are  terms  used  to  designate  various  properties  of  muscles. 

Thus,  contractility  is  the  property  the  muscle  possesses  of  short- 
ening and  of  giving  a  contraction  when  it  is  excited. 

Elasticity  is  the  general  property,  common  to  muscles  and  many 
other  bodies,  of  stretching  under  the  influence  of  a  weight  and  of 
then  returning,  more  or  less  perfectly,  to  the  first  shape. 

Tonicity  is  the  state  midway  between  extreme  contraction  and 
relaxation.  It  is  a  condition  depending  upon  the  central  nervous 
system. 

In  addition,  muscle  possesses  a  property  that  is  common  to  all 
live  tissues  and  which  is  of  fundamental  importance  in  general  physi- 
ology. It  is  irritability.  By  irritability  is  meant  that  property  of  a 
living  element  to  act  according  to  its  nature  under  the  stimulus  of 
an  excitant. 

Paralyses  have  been  observed  which  have  lasted  for  several 
months  or  even  several  years  and,  although  the  nerves  were  abso- 
lutely unexcitable,  yet  the  muscles  had  retained  their  irritability. 
This  may  be  readily  demonstrated  in  cases  of  paralysis  of  the  seventh 
pair  of  nerves. 

The  independence  of  muscle  irritability  is  formally  demonstrated 
by  experiment  in  which  the  known  action  of  the  drug,  curare,  upon 
muscles  is  taken  advantage  of.  A  watery  extract  of  this  drug,  when 
injected  into  the  blood  of  an  animal  or  introduced  beneath  its  skin, 
acts  chiefly  upon  the  motor  nerve-endings.  It  does  not,  however, 
affect  muscular  contractility.  Curare  is  an  agent  which  separates  the 
muscle-element  from  the  nerve-element  by  a  physiological  dissection 
much  superior  to  the  coarse  anatomical  dissections  which  we  could 
make. 

When  a  few  milligrams  of  this  drug  are  injected  into  the  dorsal 
l}Tnph-sac  of  a  frog,  the  poison  is  absorbed  within  a  few  minutes. 
The  animal  soon  ceases  to  support  itself,  but  lies  in  any  position  in 
which  it  may  be  placed  by  the  experimenter.  It  is  paralyzed,  produc- 
ing neither  voluntary  nor  reflex  movements.  Now,  should  the  brain 
be  destroyed,  the  skin  removed,  and  the  sciatic  nerve  stimulated  by 


468  PHYSIOLOGY. 

electricity,  no  movements  of  the  muscles  of  the  limb  follow.  On  the 
other  hand,  should  the  stimulus  be  applied  directly  to  the  muscles, 
they  immediately  contract.    Therefore  the  muscle  is  irritable  by  itself. 

By  this  it  would  seem  to  be  clearly  demonstrated  that  irritability 
belongs  to  the  muscle,  and  does  not  depend  upon  the  nerve-fibers 
mingled  with  those  of  the  muscle. 

In  addition  to  this  classical  experiment  there  may  be  mentioned 
several  other  facts  which  go  to  corroborate  what  has  been  mentioned 
concerning  irritability : — 

1.  The  chemical  excitants  of  the  muscle  are  not  the  same  as  the 
chemical  excitants  of  the  nerves.  Thus,  glycerine  excites  the  nerve, 
but  has  no  effect  upon  the  muscle. 

2.  Isolated  muscle-fibers  have  been  seen  which,  according  to 
microscopical  examination,  contained  no  nervous  elements  and  which, 
notwithstanding,   were   contractile. 

3.  If  the  decreasing  progress  of  irritability  be  followed  after 
death,  in  the  muscle  as  well  as  in  the  nerve,  it  will  be  found  that 
the  nerve  dies  long  before  the  muscle.  When  the  nerves  have  lost 
all  irritabilit}^,  the  muscle  is  still  alive,  and  can  contract  under  the 
influence  of  excitations  directly  applied  to  its  tissue.  It  is  at  that 
very  moment  when  the  nerves  have  lost  all  excitability  that  the  mus- 
cle is  at  its  maximum  of  irritability. 

Influence  of  Blood  Upon  Irritability. — It  has  been  demon- 
strated by  experiment  upon  the  frog  that  when  the  artery  of  a  mem- 
ber is  ligated  the  muscle  contraction  is  less  high  and  less  strong  than 
if  the  artery  had  been  left  intact. 

Stenon's  experiment  of  ligating  the  abdominal  aorta  of  a  dog 
is  worthy  of  mention.  In  twenty  to  thirty  minutes  after  the  ligation 
the  dog  seems  paraplegic.  He  is  unable  to  stand  upon  his  hind 
limbs.  Eeflex  and  voluntary  movements  are  completely  lost ;  muscle 
irritability,  however,  persists  for  nearly  three  hours. 

When  the  ligature  is  removed  movement  does  not  return  to  the 
limbs  at  once,  but  within  a  very  short  time  the  dog  is  able  to  stand 
upon  his  four  feet. 

Stimuli. — Those  extreme  forces  which  bring  into  play  the  irrita- 
bility of  the  muscle  are  simply  various  forms  of  energy.  To  them 
the  name  stimuli  has  been  applied.  By  their  action  the  muscle  is 
thrown  into  a  state  of  excitement  whereby  the  chemical  energy  of 
the  muscle  is  transformed  into  heat  and  work.  These  muscle 
excitants,  or  stimuli,  are  of  five  varieties:  (a)  nervous,  (b)  electrical, 
(c)  thermal,  (d)  mechanical,  and  (e)  chemical. 


THE  MUSCLES.  469 

Nervous  Stimuli. — The  most  important  of  all  the  excitatory 
forces  of  the  muscle  is  innervation.  In  the  normal  state  there  is 
scarcely  any  other  than  this  to  produce  muscle  contraction.  Our 
muscles,  as  well  as  those  of  all  other  animals,  contract  because  the 
motor  nerve  transmits  to  them  the  spontaneous  or  reflex  excitation 
of  the  nervous  centers.  The  nerve  impulses  average  about  ten  per 
second.  The  stimulus  is  exactly  proportioned  to  the  effect  which 
must  be  obtained. 

Electrical  Stimuli. — Electricity  is  employed  in  preference  to 
any  other  external  agent  to  bring  into  play  the  irritability  of  muscle. 

Thermal  Stimuli. — Thermic  excitations  also  provoke  muscular 
movements.  The  stomach  and  intestines  are  viscera  whose  muscles 
are  very  readily  excited  by  heat  and  cold.  They  contract  very  ener- 
getically when  very  cold  drinks  are  taken  and  their  temperature  is 
suddenly  modified.  On  the  contrary,  striated  muscles  hardly  react 
to  thermic  excitants.  If  heat  or  cold  be  applied  gradually,  there  is 
not  produced  any  muscle  contraction.  Excitants  act  only  when  they 
are  applied  suddenly. 

Mechanical  Stimuli. — Mechanical  excitants  that  are  capable 
of  producing  muscular  contraction  are  rather  common.  Thus,  the 
surgeon,  while  performing  an  operation,  notices  slight  fibrillary 
tremblings  following  each  stroke  of  his  scalpel. 

Chemical  Stimuli. — It  can  be  stated  as  a  rule  that  all  the 
substances  which  are  fatal  to  the  life  of  the  muscle  are  excitants  of 
the  muscle.  On  this  ground,  distilled  water  is  an  excitant,  for  when 
it  is  injected  into  the  arterial  system  of  a  frog  its  muscles  show 
fibrillary  twitchings.  Not  only  does  the  water  excite  the  muscle,  but 
it  also  kills  rapidly. 

Chemical  Constitution  of  Muscle-tissue. — The  chemical  study  of 
muscle  is  one  of  the  most  difficult  of  physiological  chemistry.  There 
are  in  the  muscle  proteid  matters  very  like  one  another  and  which 
can  be  distinguished  only  by  superficial  characters.  This  renders 
results  far  from  being  satisfactory  or  reliable. 

Besides,  it  is  necessary,  in  order  to  know  chemical  reactions  of 
muscles,  to  study  only  living  muscle.  But  from  previous  study  it 
will  be  recalled  that  even  the  weakest  chemical  actions  produce  very 
decided  changes  in  the  muscles,  with  consequent  alteration  of  its 
chemical  functions. 

Then,  too,  muscle-fiber  is  mingled  with  many  other  tissues, 
arteries,  veins,  nerves,  connective  tissues,  etc.;   the  separation  of  the 


470  PHYSIOLOGY. 

muscular  fiber  from  its  enveloping  media  is  almost  impossible  com- 
pletely to  effect. 

Reaction. — Living  muscle  is  alkaline;  however,  after  extreme 
activity  and  after  death  its  reaction  is  found  to  be  acid.  This  is 
due  to  the  development  of  sarcolactic  acid.  The  postmortem  change 
in  muscular  constitution  is  due  to  spontaneous  coagulation  of  a  pro- 
teid  Avithin  the  muscle-fibers. 

Constituents  of  Muscle. — Proteids. — Most  abundant,  myosino- 
gen  (pseudoglobulin),  paramyosinogen  (euglobuiin)  of  muscle  exist- 
ing as  one-fourth  in  amount  of  myosinogen. 

Coloring  Matter, — Myohaematin. 

Ferment. — Myosin  ferment,  and  another  ferment  in  muscle 
which,  with  the  activitor  of  the  pancreatic  juice,  destroys  sugar. 

Extractives. — (1)  Non-nitrogenous  Extractives : — 


1.  Glycogen. 

4.  Inosite. 

2.  Dextrin  and  sugars. 

5.  Fat. 

3.  Lactic  acid. 

(2)  Nitrogenous  Extractives: — 

1.  Creatin. 

6.  Urea. 

2.  Creatinin. 

7.  Carnine. 

3.  Xanthin. 

8.  Carnic  acid. 

4.  Hypoxanthin. 

9.  Inosinic  acid, 

5.  Uric  acid. 

0.  Taurine. 

Carbohydrates  of  Muscle. — (1)  Glycogen.  (2)  Lactic  Acid,  (a) 
The  optically  inactive  acid,  ordinary  lactic  acid  of  fermentations,  as 
in  milk;  small  quantity  in  muscle,  (b)  Dextro-rotary  lactic  acid. 
This  is  paralactic  or  sarcolactic  acid,  the  chief  lactic  acid  of  muscle. 

The  bulk  of  authority  tends  to  prove  that  sarcolactic  acid  mainly 
comes  from  proteid. 

Urea. — A  small  quantity  in  muscle  (0.07  to  0.02  per  cent.).  It  is 
supposed  that  most  of  the  creatin  is  broken  up  into  ammonia  before 
it  leaves  the  muscle. 

Myosin. — Myosin  is  formed  from  myosinogen,  myosin  ferment, 
and  calcium  salts. 

Syntonin. — When  a  solution  of  myosin  is  heated  it  is  altered  in 
such  a  manner  that  it  can  no  longer  be  dissolved  in  NaCl  as  before. 

If  it  be  treated  with  dilute  HCl,  it  becomes  altered  in  still 
another  manner,  and  produces  an  important  substance  which  is  called 
synionin. 


THE  MUSCLES.  471 

If  syntonin  in  HCl  solution  have  pepsin  added  to  it,  the  syntonin 
is  transformed  into  peptone. 

Muscle-serutn. — In  the  coagulation  of  blood  two  principal  com- 
ponents are  noted:  the  clot  and  the  serum  floating  upon  the  clot. 
Also,  after  coagulation  of  the  muscular  juice,  myosin  and  serum  must 
be  distinguished. 

The  muscle-serum  which  floats  upon  the  surface  of  the  myosin 
contains  several  substances. 

The  amount  of  proteid  matters  contained  in  the  muscular  tissues 
is  very  variable.  It  is  usually  stated  that  in  100  parts,  by  weight, 
of  muscle,  there  are  20  parts  of  proteid  matters. 

Extractives. — Creatinin  is  derived  from  creatin  by  dehydra- 
tion. The  amount  of  creatinin  in  muscle  is  small,  being  but  0.3  per 
cent. 

Hypoxanthin  and  xanthin  occur  to  the  extent  of  about  0.02  per 
cent. 

Halliburton  found  a  myosm-fertnent.  Its  presence  would  seem 
to  explain  the  coagulation  of  myosin. 

Glycogex. — Among  the  nonnitrogenized  substances  must  first 
be  classed  the  sugars  and  their  analogues.  Glycogen  is  the  principal 
muscle-starch.  The  glycogen  in  the  muscles  was  discovered  by 
Claude  Bernard  while  looking  for  the  glycogen  in  the  liver  of  the 
foetus  and  newborn.  He  found  in  the  muscles  of  the  embryo  quanti- 
ties of  glycogen  that  were  relatively  enormous.  Glycogen  exists  in 
all  of  the  muscles. 

The  more  active  the  state  of  a  muscle,  the  less  glycogen  it  con- 
tains. Therefore,  much  of  it  is  found  in  those  muscles  which  con- 
tract but  little. 

Muscle  extract  and  pancreatic  activator  when  mixed  together 
rapidly  destroy  sugar  in  the  blood,  probably  by  the  formation  of  a 
ferment.  Either  extract  alone  is  powerless  to  break  up  glucose. 
These  two  extracts  resemble  the  action  of  enterokinase  upon  trypsin- 
ogen. 

Inosite. — It  is  a  sort  of  crystallizable  body  that  is  unferment- 
able.  That  is,  it  does  not  ferment  to  form  alcohol,  but  lactic  acid. 
It  is  found  in  the  vegetable  kingdom  also,  where  it  is  usually  extracted 
from  peas  or  beans.  It  is  identical  with  the  inosite  of  muscle.  It 
is  not  a  sugar,  but  belongs  to  the  aromatic  series. 

Mineral  Substances. — Alkaline  phosphates  predominate.  In 
100  parts  of  ash  there  are  about  90  parts  of  phosphates.  The  metals 
found  in  muscle  are  potassium,  sodium,  and  calcium;   there  is  also 


472  PHYSIOLOGY. 

a  small  quantity  of  mfignesiuin  and  iron.  Phosphoric  acid  exists  in 
muscle  as  inorganic  phosphates,  phosphorus  of  phosphocarnic  acid, 
and  phosphorus  of  inosinie  acid.  Carnic  acid  is  identical  with  anti- 
peptone.  When  a  muscle  works  it  increases  the  phosphates  in  the 
urine.     The  gases  found  in  muscle  are  carbonic-acid  gas  and  oxygen. 

Adipocere  is  a  waxy  substance  which  replaces  muscular  tissue  if 
bodies  be  buried  in  damp  soil.  It  consists  principally  of  a  soap  made 
of  calcium  with  palmitic  and  stearic  acids. 

Rigor  Mortis. — During  rigor  mortis  the  muscles  become  rigid, 
hard,  inextensible,  shortened  and  swollen,  as  though  in  a  state  of 
contraction.  After  death,  rigor  mortis  is  a  constant  phenomenon. 
The  muscles  to  first  become  rigid  are  the  masseter,  temporal,  and 
internal  pterygoid.  Then  it  seizes  the  muscles  of  the  trunk  and 
neck,  then  the  arms  and  the  legs.  Tetanus  and  rigors  appear  in  the 
same  muscles  and  extend  to  others  in  the  same  way. 

In  rigor  mortis  the  thumb  is  in  the  palm  of  the  hand  and  covered 
with  the  other  fingers,  showing  that  the  flexor  muscles  overcome 
their  antagonistic  muscles,  the  extensors.  The  jaws  are  contracted, 
the  eyes  are  widely  open,  the  head  and  neck  are  drawn  backward,  the 
abdomen  is  depressed,  the  extremities  are  half  flexed,  and  the  feet 
are  extended. 

Cause  of  Eigek  Mortis. — It  is  due  to  the  myosinogen  becom- 
ing myosin  by  the  action  of  the  myosin  ferment  with  calcium  salts. 
During  rigor  mortis  the  muscles  become  acid,  due  to  sarcolactic  acid 
and  acid  phosphates,  the  muscle  becomes  cloudy,  and  gives  off  heat 
and  carbonic  acid.  After  some  time  rigor  mortis  passes  off  and  the 
body  becomes  relaxed.  After  fatigue  the  rigor  mortis  ensues  rapidly 
after  death,  lasts  but  a  short  time,  followed  by  putrefaction.  It  is 
well  known  that  butchers  do  not  kill  animals  tired  by  a  long  walk, 
but  wait  for  a  rest  of  some  days. 

In  man  it  is  generally  four  hours  after  death  that  cadaveric 
rigidity  becomes  complete.  As  a  rule,  it  may  be  said  that  rigidity 
begins  two  hours  after  death,  reaching  its  maximum  two  hours  later. 

A  particular  kind  of  7-igor  mortis  has  been  observed  by  military 
surgeons.  Soldiers  while  in  full  activity  have  been  struck  by  pro- 
jectiles and  have  been  seen  to  become  stiff  instantaneously.  It  is  a 
sort  of  rigor  mortis  which  seizes  all  of  the  muscles  of  the  body  imme- 
diately after  death. 

Influence  of  Temperature. — Animals  which  have  died  in  heated 
chambers  become  rigid  very  quickly  and  the  rigidity  disappears  as 
quickly. 


THE  MUSCLES. 


47-^ 


Fig.   190. — The  Pendulum  Myograph.     (Foster.) 

A,  Smoked  glass  plate,  swings  on  the  "seconds"  pendulum,  B,  by  means  of 
carefully  adjusted  bearings  at  C.  The  contrivances  by  which  the  glass  plate  can 
be  moved  and  replaced  at  pleasure  are  not  shown.  A  second  glass  plate,  so 
arranged  that  tho  first  glass  plate  may  be  moved  up  and  down  without  altering 


474  PHYSIOLOGY. 

Cold,  which  retards  chemical  phenomena,  retards  the  appear- 
ance of  cadaveric  rigidity  and  prolongs  it  enormously. 

Influence  of  Fatigue. — The  inlluence  of  prolonged  labor  of  the 
muscle  upon  the  premature  appearance  of  rigidity  is  an  indisputable 
fact. 

Muscular  Labor  and  Urea  Excretion.— With  the  ordinary  diet  of 
fats,  carbohydrates,  and  proteids,  muscular  labor  greatly  increases 
the  output  of  carbon  by  the  lungs  in  the  shape  of  carbon  dioxide, 
whilst  the  nitrogen  excreted  as  urea  is  slightly,  if  at  all,  increased. 
In  a  fasting  animal  work  increases  the  excretion  of  both  the  carbon 
and  the  nitrogen.  The  output  of  carbon  is  proportional  to  the  work 
done,  the  nitrogen  not  being  so  closely  proportional.  Here  the  mus- 
cle procures  its  energy  from  the  proteids,  whilst  the  animal  with  an 
ordinary  diet  uses  up  mainly  the  carbohydrates  and  fats. 

Hence,  in  muscular  exertion  the  chief  foods — proteids,  fats,  and 
carbohydrates — are  metabolized  in  order  to  set  free  heat  and  work. 
In  doing  this  the  muscle  prefers  to  break  up  the  fats  and  carbo- 
hydrates rather  than  the  proteids.  Hence  when  muscle  fulfills  its 
two  chief  functions,  to  produce  work  and  heat,  it  uses  up  the  fats 
and  carbohydrates  and  proteids,  but  the  proteids  are  chiefly  used  to 
build  up  and  repair  the  muscle-substance  itself. 

Sarcolactic  Acid. — ^The  production  of  sarcolactic  acid  is  the 
more  abundant  as  the  muscle  has  been  longer  and  more  strongly 
excited. 

Myograph. — The  du  Bois-Eeymond  induction  coil  is  the  one 
most  commonly  employed  in  physiological  experiments.     When  it  is 


the  swing  of  the  pendulum,  is  also  omitted.  Before  commencing  an  experiment 
the  pendulum  is  raised  up  (in  the  figure  to  the  right)  and  is  kept  in  that  position 
by  the  tooth  (a)  catching  on  the  spring-catch  (&).  On  depressing  the  catch  (h^ 
the  glass  plate  is  set  free,  swings  into  the  new  position  indicated  by  the  dotted 
lines,  and  is  held  in  that  position  by  the  tooth  (a')  catching  on  the  catch  (6')- 
In  the  course  of  its  swing  Ihe  tooth  (a'),  coming  into  contact  with  the  projecting 
steel  rod  (c),  knocks  it  on  one  side  into  the  position  indicated  by  the  dotted  line 
(c')-  The  rod  (c)  is  in  electrical  continuity  with  the  wire  (x)  of  the  primary  coil 
of  an  induction-machine.  The  screw  ((7)  is  similarly  in  electrical  continuity  with 
the  wire  {y)  of  the  same  primary  coil.  The  screw  (d)  and  the  rod  (c)  are  armed 
with  platinum  at  the  points  at  which  they  are  in  contact,  and  both  are  insulated 
by  means  of  the  ebonite  block  (e).  As  long  a^  c  and  d  are  in  contact  the  circuit 
of  the  primary  coil  to  which  x  and  y  belong  is  closed.  When  in  its  swing  the 
tooth  W)  knocks  q  away  from  d,  at  that  instant  the  circuit  is  broken,  and  a 
"breaking"  shock  is  sent  through  the  electrodes  connected  with  the  secondary 
coil  of  the  machine  and  so  through  the  nerve.  The  lever  (7),  the  end  only  of 
which  is  shown  in  the  figure,  is  brought  to  bear  on  the  glass  plate,  and  when  at 
rest  describes  a  straight  line,  or  more  exactly  an  arc  of  a  circle  of  large  radius. 
The  tuning-fork  (f),  the  ends  only  of  the  two  limbs  of  which  are  shown  in  the 
figure  placed  immediately  below  the  lever,   serves  to  mark  the  time. 


THE  MUSCLES. 


475 


necessary  to  use  very  rapid  breaking  of  the  current,  some  instrument 
must  be  employed  for  that  purpose.  The  first  instrument  used  in 
making  myograms  was  that  of  Helmholtz. 

Simple  Contraction. — If  a  single  induction  shock  be  applied  to 
a  muscle  there  will  result  a  simple  muscular  contraction;  that  is,  the 
muscle  will  respond  by  a  quick  contraction,  with  return  to  its  former 
relaxed  condition.  This  contraction,  when  graphically  shown,  is 
termed  a  simple  muscle-curve. 

Muscle-curve,  or  Myogram. — If  the  muscle-curve  of  a  single 
stimulus  be  analyzed,  it  will  be  seen  to  be  composed  of  various  eie- 


Fig.  191. — A  Muscle-curve  Obtained  by  Means  of  tlie  Pendulum 
Myograph.      (  Fosteb.  ) 

To  be  read  from  left  to  right. 

a  indicates  the  moment  at  which  the  induction-shock  is  sent  into  the  nerve. 
6,  The  commencement;  c,  the  maximum;  and  (l,  the  close  of  the  contraction. 
The  two  smaller  curves  succeeding  the  larger  one  are  due  to  oscillations  of  the 
lever. 

Below  the  muscle-curve  is  the  curve  drawn  by  a  tuning-fork  making  180 
double  vibrations  a  second,  each  complete  curve  therefore  representing  i/iso  of  a 
second.  It  will  be  observed  that  the  plate  of  the  myograph  was  traveling  more 
rapidly  toward  the  close  than  at  the  beginning  of  the  contraction,  as  shown  by 
the  greater  length  of  the  vibration-curves. 


ments,  as  follows :  (1)  period  of  latent  stimulation,  (2)  period  of  con- 
traction, and  (3)  period  of  relaxation. 

Latent  Period. — The  significance  of  this  term  is  that  the  muscle 
experimented  with  does  not  respond  at  the  precise  moment  when  the 
stimulus  is  applied  to  it.  The  response  comes  later — about  ^/joo  o^ 
a  second.  During  the  latent  period  there  is  no  apparent  change 
occurring  within  the  muscle.  The  latent  period  may  be  modified  by 
increased  stimulus  and  heat,  when  it  becomes  shortened ;  fatigue  and 
cold  lengthen  the  time.  The  latent  period  of  unstriped  muscle  may 
be  as  long  as  one  or  two  seconds. 

Contraction  Period. — The  muscle-curve  comprises  two  periods: 
that  of  the  ascent  and  that  of  the  descent  of  the  muscle.     The  ascent 


476 


PHYSIOLOGY. 


of  the  curve  represents  the  contraction  of  the  muscle  until  it  has 
reached  its  maximum.  The  rate  of  contraction  is  at  first  a  trifle 
slow,  then  more  rapid  and  more  slow  a  second  time.  The  extent  is 
Vioo  of  a  second. 

Relaxation  Period. — After  the  muscle  has  contracted  to  its  max- 
imum, it  begins  to  relax — at  first  slowly,  then  more  quickly,  and 
finally  more  slowly  again.  Its  duration  is  ^/loo  of  a  second.  It  is 
shorter  with  a  weak  stimulus  and  longer  with  a  strong  stimulus. 


Fig.    192. — Arrangement  of  Apparatus  in   Conducting  Experiments  on 
Nerve  and  Muscle.     (Stirling.) 

B,  Galvanic  battery.  K,  Electric  key  in  primary  circuit.  P,  Primary  coil 
of  induction  machine.  S,  Secondary  coil  of  induction  apparatus,  from  which 
the  current  is  conducted  when  the  key  (£')  is  open  to  the  electrode  (E)  on 
which  rests  the  nerve  in).  The  muscle  (M)  is  supported  by  a  clamp  under 
a  glass  shade,  its  tendon  being  connected  by  a  thread  with  a  lever  (L)  writ- 
ing on  the  smoked  surface  of  a  revolving  drum.  The  time-marker  (TM)  is 
included  in  the  primary  circuit  so  that  when  the  current  passes  through  P  by 
closing  the  key  (K)  it  also  traverses  the  electromagnet  of  the  time-marker 
and  causes  a  record  of  the  instant  of  stimulation  to  be  made  on  the  surface 
of  the  drum.  S,  Stand  supporting  moist  chamber.  W,  Weight  by  which  muscle 
is  stretched  and  which  is  lifted  in  the  contraction  of  the  muscle. 


In  the  myograph  we  use  a  light  lever  and  a  weight  as  near  its 
axis  as  possible  to  record  the  contraction.  Here  the  tension  of  the 
muscle  in  its  contraction  and  relaxation  remains  nearly  the  same. 
This  contraction  is  called  an  isotonic  contraction.  The  isometric 
contraction  is  produced  when  the  muscle  pulls  against  a  spring. 
Here  the  muscle  undergoes  slight  change  in  length  and  the  energy 
of  change  of  form  is  transformed  into  tension  and  stored  in  the 
spring.  An  examination  of  isometric  and  isotonic  curves  proves  that 
a  muscle  which  has  shortened  to  a  given  length  will  be  making  a  far 


THE  MUSCLES.  477 

greater  pull  when  its  effort  to  shorten  has  been  resisted  than  when 
it  has  reached  the  same  during  a  contraction  without  resistance, 
which  is  an  isotonic  contraction. 

Curve  of  Fatigue. — When  a  muscle  has  become  fatigued  and 
its  myogram  studied,  at  first  the  contractions  improve  for  a  short 


Fig.   193. — Fatigue-curves  of  Frog's  Muscle.      (Waller.) 

time.  This  is  shown  by  the  successive  contractions  being  higher. 
Afterward  the  latent  period  increases,  the  curve  becomes  less  high, 
while  the  contraction  becomes  slower  and  lasts  longer. 

Yeratrine  and  adrenalin  greatly  prolong  the  stage  of  relaxation 
in  a  muscle. 

Staircase  Coxtractioxs. — When  electrical  stimuli  of  equal 
strength  are  let  into  a  muscle  at  regular  intervals  and  the  contrac- 
tions registered,  it  is  seen  that  at  first  each  curve  exceeds  its  pre- 
decessor in  height.     It  shows  that  the  muscle  is  benefited  within  cer- 


Fig.  194. — Effect  of  Increase  of  Current  on  Efficiency  of  Breaking 
Induction  Shocks.     (Howell,  after  FiCK.) 

a,  minimal  contraction;    6,  c,  first  maximum;    d,  e,  second  maximum. 

tain  limits  by  contraction,  and  its  excitability  increased  for  a  new 
stimulus,  just  as  we  can  do  better  muscular  work  when  we  have 
warmed  up  our  muscles.  Bowditch  first  noticed  the  staircase  con- 
traction in  cardiac  muscle. 

Compositiox  of  Muscle  Before  axd  After  Contraction. — 
Experiments  show  that  constant  chemical  metabolism  is  going  on 
in  a  muscle  at  rest.     It  is  constantly  taking  in  oxygen,  glucose,  and 


478 


PHYSIOLOGY. 


perhaps  fats  and  proteids,  and  giving  off  carbonic  acid.  When  the 
muscle  becomes  active  and  does  work,  then  the  chemical  changes 
become  more  active. 

The  chief  differences  between  resting  and  acting  muscle  are: 
(1)  the  acting  muscle  forms  more  CO, ;  (2)  more  oxygen  is  consumed ; 
(3)  sarcolactic  acid  is  formed;  (4)  glycogen  is  made  use  of;  (5)  the 
substances  soluble  in  water  diminish  in  amount,  while  those  soluble 
in  alcohol  increase. 

Changes  in  the  Volume  of  the  Muscle  During  Contrac- 
tion.— Muscular  contraction  can  be  defined  by  its  apparent  effects: 


Fig.  195. — An  Experiment  to  Show  that  a  Contracting  Muscle  does 
not  Change  its  Volume.      (Hedon.) 

V,  Vessel  filled  with  water  containing  the  frog's  foot,  the  nerve  upon  two 
electrodes,  t,  Capillary  tube  In  which  the  level  of  the  water  is  observed.  P, 
Battery. 


a  shortening  of  the  muscle.  By  experiment  it  has  been  shown  that 
the  muscle  on  contracting  simply  shifts  its  muscular  units  when  it 
shortens,  for  the  volume  of  the  muscle  remains  the  same. 

Muscle-wave. — When  a  muscle  is  placed  beneath  two  levers 
some  distance  apart,  and  one  end  of  the  muscle  is  stimulated,  then 
a  wave  of  muscular  contraction  runs  through  it.  The  distance 
between  the  points  at  which  the  two  curves  begin  to  rise  from  the 
abscissa  gives  the  rate  of  wave-movement. 

The  continuity  of  the  muscle-fiber  is  the  reason  the  wave  is 
propagated.     The   fibers   stimulated   are   set  into   activity   and   the 


THE  MUSCLES. 


479 


evolution  of  energy  in  them  stimulates  the  neighboring  fibers  and 
the  contraction  passes  along  the  muscle. 


The  velocity  of  a  contraction-wave  in  muscle  can  be  measured; 
in  the  frog  it  is  from  three  to  four  meters  per  second;  in  man,  about 
forty  feet  per  second. 


480  PHYSIOLOGY. 

The  Effects  of  Two  Successive  Stimuli. — Let  the  student  imagine 
two  successive  nionieiitary  stimuli  applied  successively  to  a  muscle. 
The  stimuli  may  l)e  either  maximal  or  submaxim,aJ;  that  is,  either 
the  greatest  possible  contraction  the  muscle  is  able  to  accomplish  or 
only  a  medium  contraction  from  the  applied  stimulus. 


Fig.  197. — Rate  of  Conduction  of  the  Contraction  Process  along  a 
Muscle  as  shown  by  the  DiiTerence  in  the  time  of  Thickening  of  the  two 
Extremities.      (Marey,  Howell.) 

The  tuning-fork  waves  record  ^/mo  of  a  second. 

If  each  of  the  two  stimuli  be  maximal,  the  effects  produced  will 
vary  according  to  the  time  of  application  of  the  two  excitants.  Thus, 
(1)  if  the  second  stimulus  be  applied  after  the  relaxation  following 
the  effect  of  the  first  stimulus,  then  the  myogram  shows  two  maximal 


Fig.   198. — Tracing  of  a  Double  Muscle-curve.      (Foster.) 

To  be  read  from  left  to  right. 

While  the  muscle  was  engaged  in  the  first  contraction  (whose  complete 
course,  had  nothing  intervened,  is  indicated  by  the  dotted  line),  a  second 
induction  shock  was  thrown  in  at  such  time  that  the  second  contraction  began 
just  as  the  first  was  beginning  to  decline.  The  second  curve  is  seen  to  start 
from  the  first  as  does  the  flrct  from  the  base  line. 

contractions;  (2)  if  the  second  stimulus  follow  the  first  with  such 
rapidity  that  the  two  occur  during  the  latent  period  of  the  muscle- 
curve,  then  the  recording  instrument  shows  but  one  maximal  con- 
traction. 


THE  MUSCLES. 


481 


If  the  two  stimuli  be  nonmaximal,  the  effects  of  the  two  separate 
stimuli  will  be  superimposed ;  that  is,  there  will  be  a  summation  of 
the  contractions.  This  summation  occurs  regardless  of  the  time  of 
application  of  the  stimuli. 

Summation  of  Stimuli. — As  the  second  stimulation  was  just  seen 
to  add  its  curve  to  the  first,  so  does  the  third  add  itself  to  the  second, 


Fig.  199. — Progress  in  Fusion  of  Contraction.      (Laulanie.) 
A  G,  B  7,  C  8,  per  second. 

the  fourth  to  the  third,  etc.  If  the  excitations  occur  with  a  rhythm 
that  is  not  too  rapid,  the  various  shocks  are  nearly  equal,  as  shown 
by  the  myogram,  but  yet  they  do  not  mingle.  These  isolated  shocks 
are  seen  when  the  rhythm  does  not  exceed  six  per  second. 

If,  now,  these  same  excitations  be  repeated  with  a  frequency  of 
twenty  per  second,  isolated  shocks  will  not  be  seen.  Each  stimulus, 
lasting  but  V20  of  a  second,  does  not  allow  the  muscle  completely  to 

31 


482 


niYSIOI.OGY. 


relax;  thus,  the  second  contraction  encroaches  upon  the  first,  the 
third  upon  the  second,  etc.  From  the  rapid  succession  of  the  stimuli, 
the  muscle  remains  in  a  condition  of  continued  viljratory  contraction. 
I'hat  is,  in  a  stale  of  Irlanus. 

Complete  Tetanus.— If  the  excitation  rhythm  be  more  frequent, 
— say,  fifty  of  them  per  second, — there  will  no  longer  be  any  trace 
of  the   primitive   shocks.      The   ascent  of  the  muscle-curve   will  be 


Fig.  200. — 1.  Imperfect  Tetanus,  15  Contractions  per  second. 
2.  Perfect  Tetanus.     (Laulani^.) 

abrupt  and  decided;  the  contraction  due  to  the  first  shock  will  not 
be  followed  by  any  relaxation.  There  will  be  no  oscillation  recorded 
upon  the  myogram.  The  upper  straight  line  due  to  the  complete 
contraction  of  the  muscle  is  called  the  plateau.  When  the  muscle 
is  in  this  condition  the  tetanus  is  said  to  be  perfect  or  complete. 

The  tetanus  is  spoken  of  as  incomplete  when  there  are  still  relax- 
ations and  vibrations  which  indicate  the  incomplete  mingling  of  the 
shocks. 

The  number  of  stimuli  that  are  required  to  produce  tetanus  may 
be  very  variable.  Fifteen  to  twenty  stimuli  per  second  suffice  to 
throw  a  frog's  muscle  into  tetanus. 


THE  MUSCLES.  483 

Duration  of  Tetanus. — A  tetanized  muscle  cannot  be  kept  con- 
tracted for  a  considerable  length  of  time,  even  though,  the  stimuli 
be  kept  constant.  The  muscle  begins  to  elongate — at  first  some- 
what quickly,  but  later  more  slowly.  This  change  is  produced  by 
fatigue  of  tbe  muscle. 

Effect  of  Temperature  on  Muscle-curve. — Low  temperature  makes 
the  contraction  longer  and  lower;  the  latent  period  is  longer,  and 
the  relaxation-curve  is  greatly  not  unlike  that  of  a  fatigued  muscle. 
When  the  temperature  is  raised,  the  setting  free  of  energy  is  more 
rapid;  hence  the  time  of  contraction  is  shortened,  especially  the 
latent  period  ard  time  of  shortening  of  the  muscle. 

Strength  of  Stimulus. — If  you  apply  a  current  just  sufficient  to 
cause  a  muscle  to  contract,  and  then  increase  the  strength  of  the 
current,  the  muscular  contraction  will  become  more  rapid  and  more 
complete.  But  the  increase  in  contraction  is  not  proportional  to  the 
increase  in  stimulus.  As  the  stimulus  is  gradually  increased,  the 
increase  in  contraction  becomes  smaller  and  smaller.  After  a  cer- 
tain strength  of  stimulus  is  attained,  a  further  increase  of  it  does 
not  cause  any  increment  in  the  contraction  of  the  muscle. 

Amount  of  Load. — If  a  muscle  is  attached  to  a  lever  without  any 
weight  in  the  scale-pan,  it  is  ascertained  that  light  weights  actually 
increase  the  height  of  the  contraction,  whilst  heavier  weights  dimin- 
ish it  until  a  limit  is  reached,  and  when  a  sufficient  weight  is  used 
the  muscle  no  longer  contracts. 

Muscle-tonus. — This  is  a  condition  of  a  muscle  more  or  less 
stretched,  and  is  dependent  upon  the  reflex  activity  of  the  central 
nervous  system  and  a  sufficient  supply  of  blood  to  the  muscle.  If 
you  cut  a  motor  nerve  going  to  a  muscle,  the  muscle  loses  its  tonus. 
If  you  divide  all  the  posterior  spinal  roots,  then  the  muscles  also  lose 
their  tonus. 

Muscle-sound. — Helmholtz  said  that  36  vibrations  per  second 
formed  the  average  for  the  production  of  muscular  tones.  To-day 
this  is  considered  an  overtone,  and  the  requisite  number  of  necessary 
vibrations  is  placed  at  19  per  second. 

First  Heart-sound. — It  is  probable  that  the  first  sound  of  the 
heart  is  partly  a  muscle-sound.  It  is  a  dull  sound,  persisting  when 
the  thorax  is  taken  away  and  the  auriculo-ventricular  valves  are  de- 
stroyed. The  sound  could  not  in  such  an  instance  be  produced  by 
the  vibration  of  the  valves. 

Voluntary  Contraction. — The  number  of  single  impulses  sent  to 
our   muscles   during   voluntary   movements   are    somewhat   variable. 


484  PHYSIOLOGY. 

There  are  from  8  to  12  impulses  for  a  slow  movement  and  from  18 
to  20  impulses  per  second  for  a  rapid  movement.  Ten  vibrations 
per  second  ma}^  ))e  taken  as  the  average. 

Elasticity  of  the  Muscle. — Of  all  the  properties  of  muscle,  elas- 
ticity is  the  one  least  well  known,  the  one  which  is  most  difficult  to 
explain  and  understand. 

Physicists  say  that  a  body  is  perfectly  elastic  when,  after  having 
been  removed  from  its  first  position,  it  returns  exactly  to  the  original 
position.  Thus,  an  ivory  ball  is  perfectly  elastic;  after  it  has  been 
flattened  by  an  external  force  it  returns  exactly  to  its  original  shape. 


Fig.   201. — Extensibility  of  Elastic  Band  and  Muscle.      (Waller.) 

If  a  piece  of  rubber  is  stretched  by  adding  successive  weights  it 
is  found  that  the  series  of  elongations  are  nearly  proportional  to  the 
weights.  When  the  weights  are  successively  removed  it  will  be  found 
that  the  elasticity  of  the  rubber  is  nearly  perfect.  But  if  over- 
weighted for  a  long  time  it  does  not  return  completely  to  its 
original  length,  and  the  elasticity  disappears  gradually.  If  now  you 
take  a  frog's  fresh  muscle  and  successively  load  it,  the  extension  of 
the  muscle  for  each  weight  is  not  proportional  to  the  weight  used, 
but  with  each  increase  in  weight  the  muscle  stretches  rather  less,  the 
greater  the  previous  extension.  On  removing  the  weights  the  muscle 
shortens  but  it  does  not  return  to  its  original  length.  A  contracted 
muscle  is  more  extensible  than  a  resting  one.  This  prevents  a  rup- 
ture of  the  muscle  in  a  sudden  contraction. 

Muscular  elasticity  preserves  the  tension  of  the  muscle  under 


THE  MUSCLES. 


485 


all  usual  conditions.  The  muscles  attached  to  the  bones  are  in  a 
state  of  elastic  tension  which  is  favorable  to  the  action  of  the  muscle, 
diminishing  the  danger  of  rupturing  its  fibers.  The  elasticity  of 
muscle  favors  the  economical  expenditure  of  work  by  the  muscle.  A 
muscle  is  always  taut,  never  in  a  state  of  relaxation,  and  it  is  then 
ready  to  efficiently  exert  mechanical  force  the  moment  it  begins  to 
contract.  Heating  to  a  certain  extent  increases  and  cooling  decreases 
elasticity.  The  curve  of  muscle,  when  stretched  by  weights,  is  not 
a  hyperbola,  but  one  peculiar  to  muscle. 


In  rgor 


lu  tetanus 


Fatigued 


Fig.  202.— Extenaibility  of  Muscle  in  Various  States.      (Waller.) 
Tested  by  50  grammes  applied  for  short  periods. 

Muscular  Work. — While  treating  of  elasticity  and  its  modifica- 
tion, tonicity,  it  might  be  well  to  give  a  brief  discussion  upon  mus- 
cular work.  The  amount  of  mechanical  work  which  a  muscle  per- 
forms equals  the  product  of  the  weight  lifted  and  the  height  to  which 
the  weight  is  lifted.    Thus,  the  work  =  height  X  the  weight. 

When  a  muscle  begins  to  contract,  it  is  then  that  it  lifts  the 
greatest  load;  as  the  contraction  continues,  the  muscle  is  capable  of 
lifting  less  and  less. 


486  PHYSIOLOGY. 

If  the  height  he  expressed  in  feet  and  the  weight  in  pounds,  then 
the  work  performed  is  measured  in  units  of  foot-pounds.  Likewise, 
should  the  height  he  measured  in  meters  and  the  weight  in  grams, 
then  the  work  done  is  expressed  in  grammeters. 

In  studying  tlie  heights  of  contraction  in  a  loaded  muscle  it  is 
found  that  the  heights  of  lift  continuously  diminish,  but  the  actual 
work  done  by  the  muscle  increases  rapidly  and  then  more  slowly  until 
it  reaches  its  maximum  with  a  load  of  200  grams.  After  that  point 
the  work  done  slowly  decreases  and  then  more  rapidly  until  it  receives 
a  load  of  700  grams,  when  the  muscle  is  unable  to  contract. 

Dynamometer. — The  common,  clinical  form  of  dynamometer  is 
much  used  to  determine  the  absolute  force  of  certain  muscles.  The 
instrument  is  very  useful  to  determine  the  difference  in  grip  between 
the  two  hands  in  cases  of  paralysis.  The  patient  grasps  the  instru- 
ment in  his  hand  and  squeezes  upon  it ;  the  power  exerted  is  regis- 
tered in  kilograms. 

Muscles  are  Most  Perfect  Machines. — They  take  the  best  ad- 
vantage of  the  fuel  supplied  to  them  and  give  in  return  a  very  high 
percentage  of  energy  in  the  form  of  work.  They,  by  legitimate  exer- 
cise, increase  in  strength  and  power  so  that  they  progressively  per- 
form more  work. 

The  steam  engine,  to  which  muscles  are  frequently  compared,  is 
inferior  in  every  respect.  The  best-made  steam  engine  shows  as 
work  only  about  12  per  cent,  of  the  total  energy  supplied  to  it  by  the 
oxidation  of  the  coal,  while  about  88  per  cent,  is  transformed  into 
heat.  Muscle  transforms  25  per  cent,  of  its  energy  into  work  and  75 
per  cent,  into  heat  to  warm  itself. 

The  proportion  of  work  to  heat  is  not  a  fixed  one.  If  you  gradu- 
ally increase  the  stimulus,  both  work  and  heat  increase ;  but  the  heat- 
production  is  increased  more  rapidly  and  reaches  its  maximum  sooner. 
Heat-production  decreases  more  rapidly  than  the  amount  of  work  pro- 
duced, when  the  muscle  is  exhausted.  When  the  muscle  is  loaded 
so  it  cannot  contract,  or  an  unweighted  muscle  is  made  to  contract, 
no  work  is  produced  and  all  the  energy  is  converted  into  heat. 

Fatigue. — Fatigue  is  due  to  a  chemical  and  physiological  altera- 
tion of  the  muscles.  It  is  characterized  by  a  pain,  more  or  less  acute, 
localized  in  the  muscles.  The  alterations  in  the  muscles  fatigued 
are  due  to  an  accumulation  of  toxic  products  of  the  metabolism  of 
the  muscle.  Sarcolactic  acid  is  one  of  these  fatigue-products,  and 
when  applied  to  a  muscle  it  causes  a  state  of  exhaustion.  Whatever 
the  fatigue-products  may  be,  a  muscle  exhausted  by  a  series  of  con- 


THE  MUSCLES. 


487 


tractions  is  saturated  with  the  so-called  fatigue-products  which  have 
poisonous  properties.  The  chemical  theory  of  fatigue  is  proved  by 
preparing  a  watery  extract  of  muscles  exhausted  by  a  series  of  con- 
tractions, and  injecting  this  into  the  circulation  of  a  frog.  Here  it 
will  cause  the  muscles  to  show  fatigue  in  the  same  manner  as  when 
spontaneously  caused.  This  fatigue  of  the  muscles  in  the  frog, 
caused  by  electric  tetanus,  can  be  removed  and  their  irritability  re- 
stored by  the  injection  of  solutions  of  sodium  carbonate  into  the  vein. 
Tliis   alkaline    solution    washes    out    the    fatigue-products    from    the 


Fig.   203. — Mosso's   Ergngraph.      (From   Tigerstedt's   "Human   Physiol- 
ogy," copyright,  190{),  by  D.  Appleton  and  Company.) 

muscle.  The  circulation  of  blood  normally  washes  away  the  toxic 
products  of  fatigue.  Mosso  has  shown  that  the  blood  of  a  fatigued 
dog,  when  injected  into  the  vein  of  another  dog.  caused  all  the  symp- 
toms of  fatigue.  In  the  fatigued  muscles  of  the  frog  it  is  not  neces- 
sary to  have  the  blood  wash  away  the  products  of  fatigue,  for  it  has 
been  shown  that  the  oxygen  of  the  air  in  about  half  an  hour  can 
restore  their  irritability.  If  the  muscle  fatigued  is  placed  in  an 
atmosphere  of  hydrogen,  no  restoration  of  the  muscle  ensues.  Oxida- 
tion is  the  restorative  agent  in  fatigued  muscles. 

The  Seat  of  the  Fatigue. — When  a  nerve  of  a  warm-blooded 
animal  is  curarized,  artificial  respiration  being  kept  up,  and  elec- 
tricity applied  to  the  nerve,  it  causes  no  muscular  response  until  the 
curare  is  excreted,  when  the  muscle  again  contracts,  showing  that  it 


488 


PHYSIOLOGY. 


is  not  tlie  nerve  or  tlie  muscle,  but  the  motor  end-plates,  which  are 
exhausted.  Mosso  has  shown  that  if,  with  the  ergograph,  you  lift  a 
weight  until  the  flexor  muscle  is  exhausted,  and  then  induction  cur- 
rents are  applied  to  tiie  nerves  going  to  the  muscle,  the  muscle  will 
again  lift  the  weight.  This  experiment  shows  that  the  fatigue- 
products  generated  in  the  muscle  are  carried  by  the  circulation  to 
the  central  nervous  system  and  poison  it.  Hence  the  central  nervous 
system  is  shown  to  be  the  chief  seat  of  fatigue,  and  the  motor  nerve- 
endings  the  next. 


A  B 

Fig.  204. — Ergographic  Curves.  (After  Mosso.)  (From  Tiger- 
stedt's  "Human  Physiolog\',"  copyriglit,  1906,  by  D.  Appleton  and  Com- 
pany. ) 

Read  from  right  to  left. 

Ergographic  Curves. — The  most  salient  feature  seen  in  them  is 
the  rhythmical  rise  and  fall,  which  is  due  to  the  central  nervous  sys- 
tem. During  the  first  180  contractions  the  height  of  the  ergographic 
curve  decreases,  and  then  becomes  nearly  constant  in  the  height,  which 
is  above  85  per  cent,  of  the  original  contraction. 

The  curve  indicates  that  during  a  series  of  contractions  two  pro- 
cesses are  at  work,  the  one  using  of  material  and  the  other  an  accu- 
mulation of  fatigue-products  in  the  first  part  of  the  curve.  In  the 
subsequent  part  of  the  curve,  the  fatigue-products  are  removed  by 
the  circulation,  and  the  circulation  supplies  the  materials  to  be 
used  up. 


THE  MUSCLES. 


489 


Involuntary  Muscle. — The  same  sul)stances  are  found  in  plain 
muscle  as  in  striated  muscle,  except  that  plain  muscle  contains  six 


Fig.  205. — Ergographic  Curve  of  a  Case  of  Addison's  Disease,  Show- 
ing Rapid  Exhaustion  of  Muscle.      (Langlois.  ) 

Read  from  right. 

times  more  neucleoproteid  than  striped  muscle.    In  its  contraction  the 
latent  period  is  ahout  a  second,  and  the  contraction  lasts  several  sec- 


Fig.  20G.— Pick's  Work  Adder 


The  wheel  (rf)  bears  upon  its  axle  a  counterpoised  muscle  lever  (c),  ending 
in  a  pawl  (w),  through  which  the  wheel  is  caused  to  revolve  when  the  lever  is 
pulled  upward  by  the  attached  muscle.  A  second  pawl  («)  prevents  the  wheel 
from  turning  bark  when  the  muscle  relaxes.  On  the  other  side  the  axle  of  the 
wheel  bears  a  pulley  from  which  a  weight  (d)  is  suspended.  The  turning  of  the 
wheel  winds  the  suspending  cord  upon  the  pulley  and  raises  the  weight  ('/). 
The  muscle  preparation  should  be  the  double  adductor,   suggested  by  Fick. 

onds;    it  spreads  as  a  wave  from  filler  to  fiber.     Its  irritability  is 
very   dependent   upon   temperature;    heat   decreases    its   tonus,    cold 


490 


PHYSIOLOGY. 


increases  it.  The  stimuli  to  excite  plain  muscle  are  chemical, 
mechanical,  and  the  opening  and  closing  of  a  constant  current. 
Organs  containing  unstriped  muscle  frequently  exhibit  involuntary 
rhythmical  movements  and  a  tendency  to  sustained  tonic  contrac- 
tion. The  force  of  the  uterus  in  expelling  the  child  and  that  of  the 
bladder  in  expelling  the  urine  show  that  plain  muscle  can  do  con- 
siderable work.  Ordinarily,  organs  made  up  of  nonstriated  muscle 
are  only  faintly  sensitive.  These  rhythmic  contractions  and  relaxa- 
tions, like  the  tonic  contractions,  are  independent  of  the  action  of 
nerves,  but  are  modified  by  it.     Unstriped  fiber  does,  like  striped 


Fig.  207. — Curve  of  Contraction  of  the  Unstriped  Muscle  of  Muller 
in  Dog.     (Laulanie.) 

The   intervals  on  the  line   T  are  seconds. 

fiber,  increase  its  height  of  contraction  by  increasing  the  strength 
of  the  stimulus.  It  can  not  be  thrown  into  a  state  of  tetanus  by  a 
series  of  stimuli.  Rapid  stimuli  simply  increase  the  force  and  rate 
of  individual  contractions.  Smooth  muscle,  as  a  rule,  contains  nerve- 
plexuses  and  ganglion-cells.  It  has  two  kinds  of  functionally  different 
nerves,  motor  and  inhibitory.  Both  sets  of  nerves  are  connected  with 
nerve-cells  in  their  course,  such  as  the  plexuses  of  Auerbach  and 
Meissner  in  the  intestinal  tract. 


CHAPTER    XII. 

VOICE   AND   5PEECH. 

It  has  long  been  established  that  the  sounds  of  the  voice  in  man 
and  mammalia  are  produced  by  the  vibratory  action  of  the  vocal  cords. 
It  is  usually  the  blast  of  expired  air — under  certain  circumstances  the 
inspiratory  blast  also — in  its  passage  through  the  glottis  that  causes 
the  tense  vocal  cords  to  vibrate.  These  cords  vibrate  according  to 
tiie  laM's  which  regulate  the  vibration  of  stretched  membranous  cords. 
As  a  result  of  these  vibrations  sound  is  produced  which,  in  man,  is 
capable  of  being  so  modified  as  to  constitute  articulate  speech. 

Experiments  upon  living  animals  show  that  the  vocal  cords  alone 
are  tlie  essential  factors  in  the  production  of  sound.  For.  so  long 
as  these  remain  untouched,  although  all  other  parts  in  the  interior  of 
the  larynx  are  destroyed,  the  animal  is  still  able  to  emit  vocal  sounds. 

The  existence  of  an  opening  in  the  larynx  of  a  living  animal,  or 
of  man,  above  the  glottis  in  no  way  prevents  the  formation  of  vocal 
sounds;  however,  should  sueli  an  opening  occur  in  the  trachea,  it 
causes  total  loss  of  voice.  By  simply  closing  the  opening  sounds  can 
be  again  produced.  Such  openings  in  man  are  usually  met  with  as 
the  result  of  accident,  of  suicidal  attempts,  or  of  operations  performed 
upon  the  larynx  or  trachea  for  the  relief  of  disease. 

Production  and  Modification  of  Sounds. — Whenever  a  solid  body 
surrounded  by  air  is  tlirown  into  vil)ration  the  sensation  of  sound  is 
carried  to  the  ear.  The  vibrations  must,  however,  be  of  certain 
strength  and  follow  one  another  with  certain  rapidity.  It  is  usually 
stated  that  if  the  vibrations  l)e  fewer  than  32  or  exceed  33,768  per 
second  no  effect  is  produced  upon  the  nerve  of  hearing. 

For  the  production  of  a  musical  sound  the  vibrations  must  suc- 
ceed each  other  at  regular  intervals ;  if  the  vibrations  occur  at 
irregular  intervals,  only  a  noise  results. 

The  pitch  of  a  sound  depends  upon  the  number  of  vibrations 
within  a  given  period  of  time.  The  pitch  becomes  higher  in  direct 
proportion  to  the  rate  of  increase  in  the  rapidity  of  the  vibrations. 

The  strength,  or  intensity,  of  the  sound  depends  upon  the  extent 
of  the  vibratory  action  of  the  sonorous  body. 

Tone,  or  timbre,  is  that  peculiar  character  of  a  musical  note 
whereby  it  can  at  once  be  distinguished  from  another  note  of  exactly 
the  same  pitch  and  strength. 

(491) 


492  PHYSIOLOGY. 

THE  ORGAN  OF  VOICE. 

The  special  organ  of  voice  in  man  is  that  portion  of  the  air- 
passages  called  the  larynx.  It  is  a  sort  of  hollow  chamber  which 
extends  from  near  the  root  of  the  tongue  to  the  first  ring  of  the 
trachea.  It  is  placed  in  the  middle  line  of  the  neck,  where  it  forms 
a  considerable  ])rojcction,  larger  above  than  below. 

Although  the  larynx  is  the  proper  organ  of  voice,  yet  the  lungs 
and  the  moving  parts  of  the  thorax  serve  to  propel  the  air  through 
this  organ.  The  cavities  above  it.  including  the  pharynx,  mouth,  and 
nasal  cavities,  assist  in  modifying  the  vocal  sounds.  They  are,  there- 
fore, adjunct  organs  of  voice. 


Fig.  20S. — The  Larynx  as  Seen  with  the  Laryngoscope.      (Landois.) 

L.,   Tongue.     A'.,    Epiglottis.     V.,   Vallecula.     R.,   Glottis.     L.    r..  True   vocal 

cords.     /R.    iM.,    Sinus    Morgagni.     L.    i\    s..    False   vocal    cords.     P.,  Position   of 

pharynx.     .S'.,    Cartilage  of   Santorini.     W.,    Cartilage   of  Wrisberg.  »S'./>.,    Sinus 
pyriformis. 

Anatomy  of  the  Larynx. — The  larynx  consists  of  a  cartilaginous 
skeleton  which  constitutes  its  walls ;  also  vocal  cords ;  muscles  which 
move  directly  the  cartilaginous  pieces,  and  influence  indirectly  the 
tension  of  the  cords;  and  finally,  a  mucous  membrane  which  lines 
the  internal  cavity. 

Cartilages. — The  cartilages  of  the  larynx  are  four  in  number: 
two  unlike  and  two  alike.  One  of  the  former  is  inferior  and  exists 
in  the  form  of  a  signet-ring.  It  is  the  cricoid.  This  cartilage  is 
continuous  with  the  rings  of  the  trachea.  Its  narrower  portion  is 
situated  anteriorly ;  its  wider  portion  is  placed  posteriorly.  It  ar- 
ticulates with  the  inferior  cornua  of  the  thyroid  cartilage,  forming 
the  crico-thyroid  articulation. 

The  other  odd  cartilage,  the  superior  one,  is  called  the  tliyroid. 
It  is  composed   of  two  quadrilateral   laminae  which   meet   in   front 


VOICE  AND  SPEECH. 


493 


at  an  angle.  This  projection  is  popularly  known  as  Adam's  apple. 
Each  thyroid  lamina  terminates  posteriorly  in  two  horns:  one  su- 
perior, the  other  inferior. 

The  two  cartilages  which  are  alike  are  the  arytenoids.  Each 
one  is  in  the  form  of  a  triangular  pyramid,  whose  base  is  movably 
articulated  at  the  back  on  the  cricoid  cartilage.  The  apex  of  each 
arytenoid  cartilage  has  attached  to  it,  in  the  shape  of  a  movable 
point,  a  cartilage  of  Saniorini. 

The  true  vocal  cords  are  attached  to  the  anterior  angles,  or 
vocal  processes,  of  the  arytenoids;  the  crico-aiytenoideus  muscles 
are  inserted  into  the  external  angles. 


Fig.  209. — Action  of  tlie  Muscles  of  tlie  Larynx.      (Beaunis.) 

The  dotted  line  indicates  the  new  positions  assumed  by  the  thyroid  carti- 
lage in  the  action  of  the  crico-thyroid  muscle.  1,  Cricoid  cartilage.  2, 
Arytenoid  cartilage.  3,  Thyroid  cartilage.  4,  True  vocal  cord.  5,  New  posi- 
tion of  the  thyroid  cartilage.     6,   New  position  of  vocal  cords. 

The  cartilages  of  Wrisberg  are  found  in  the  aryteno-epiglottic 
folds. 

The  epiglottis  is  attached  to  the  inner  surface  of  the  anterior 
portion  of  the  thyroid  cartilage.  It  projects  upward  behind  the  base 
of  the  tongue.  The  epiglottis  is  attached  to  the  tongue  by  the  three 
glosso-epiglottic  folds. 

The  false  vocal  cords  are  two  folds  of  the  laryngeal  mucous  mem- 
brane which  pass  from  the  anterior  surfaces  of  the  arytenoids  to  the 
thyroid  cartilage.    They  are  located  above  the  true  vocal  cords. 

The  true  vocal  cords  extend  from  the  anterior  angles  of  the  bases 
of  the  arytenoids  to  the  thyroid  cartilage. 

The  glottis  is  the  chink  between  the  true  vocal  cords. 

The  ventricle  of  the  larynx  is  the  pouch  between  the  true  and 
false  vocal  cords. 


494 


PHYSIOLOGY. 


The  Muscles. — All  of  the  laryngeal  cartilages,  joined  together 
by  ligaments,  are  moved  by  five  pairs  of  muscles.  The  muscles  of  the 
larynx  are  divided  into  two  groups:  intrinsic  and  extrinsic.  To  the 
former  group  belong  those  muscles  which  are  attached  to  the  various 
cartilages.  The  latter  collection  comprises  the  musculature  connect- 
ing the  hirynx  to  other  parts  like  the  hyoid  bone. 

Intrinsics. — Of  these  there  are  five  pairs. 

1.  TJie  Crico-tliyroid  Muscles. — Thci^e,  which  are  in  the  anterior 
part  of  the  larynx,  originate  in  the  front  and  sides  of  the  cricoid  car- 
tilage below.     Outwardly  they  are  attached  on  each  side  to  the  lower 


Fig.  210. — Schematic  Horizontal  Section  of  Larynx.      (Landois.) 

/,  Position  of  horizontally  divided  arytenoid  cartilages  during  respiration. 
From  their  anterior  processes  run  the  converging  vocal  cords.  The  arrows 
show  the  line  of  traction  of  the  posterior  crico-arytenoid  muscles.  //,  //, 
Position  of  the  arytenoid  muscles  as  a  result  of  this  action. 


edge  of  the  thyroid  cartilage.  They  become  fixed  by  the  action  of 
the  thyro-hyoid,  sterno-thyroid,  and  laryngo-pharyngeal  muscles. 

Action. — They  incline  the  cricoid  cartilage  upward  and  backward 
and  so  elongate  and  stretch  the  vocal  cords,  at  the  same  time  contract- 
ing the  opening  of  the  glottis. 

2.  The  Posterior  Crico-arytenoid  Muscles. — These  take  their  de- 
parture from  the  posterior  surface  of  the  shield  of  the  cricoid  cartilage. 
They  then  converge  and  are  fastened  to  the  base  of  the  corresponding 
arytenoid  cartilage. 

Action. — In  contracting  they  turn  the  anterior  ends  of  the  aryte- 
noids outward,  whereby  they  separate  the  vocal  cords  from  each  other 


VOICE  AND  SPEECH.  495 

and   give   a   rhomboid   form   to   the   glottis.     Thus   it  is  materially 
widened, 

3.  The  Lateral  Crico-arytenoids. — These  muscles  are  found  upon 
the  inner  side  of  the  cricoid.  They  are  carried  backward  and  upward 
and  are  fastened  to  the  outside  of  the  posterior  ends  of  the  bases  of 
the  arytenoid  cartilages. 

Action. — In  contracting  they  rotate  the  arytenoid  cartilage  in- 
ward. They  are  antagonists  of  the  posterior  crico-arytenoid  muscles; 
they  narrow  the  vocal  part  of  the  glottis. 

4.  The  Thyro-anjtenoid  Muscles. — This  pair  of  muscles  is  inserted 
at  the  anterior  end  in  the  middle  of  the  angle  of  the  thyroid  cartilage, 


Fig.  211. — Schematic  Closure  of  the  Glottis  by  the  Thyro-arytenoid 
Muscles.     (  Landois.  ) 

//,  //,  Position  of  the  arytenoid  cartilages  during  quiet  respiration.  The 
arrows  indicate  the  direction  of  muscular  traction.  I,  I,  Position  of  the 
arytenoid  cartilages  after  the  muscles  contract. 

and  at  the  posterior  end  it  is  fastened  to  the  inside  of  the  anterior  end 
of  the  base  of  the  arytenoid  cartilages.  Each  muscle  of  the  pair 
runs  its  entire  length  parallel  with  the  corresponding  vocal  cord. 

This  muscle  has  two  bundles :  an  internal  and  external  bundle. 
The  muscle  draws  the  arytenoids  toward  the  thyroid  and  relaxes  the 
cords.  By  the  internal  bundle  the  anterior  part  of  the  vocal  cord 
can  be  tightened  while  relaxing  the  posterior  part.  It  is  the  muscle 
concerned  in  the  production  of  the  high  notes  in  the  singing  voice. 

5.  The  arytenoid  constitutes  an  odd  muscle.  It  extends  pos- 
teriorly between  the  two  arytenoid  cartilages.  The  muscle  is  divided 
into  two  layers:  one  posterior,  of  oblique  fibers  disposed  like  an  X; 
and  one  anterior,  of  transverse  fibers. 


49b  PHYSIOLOGY. 

Its  action  is,  in  contracting,  to  draw  the  arytenoid  cartilages 
together  so  that  the  respiratory  part  of  the  gh)ttis  is  closed.  If  the 
contraction  be  simultaneous  with  that  of  the  lateral  crieo-arytenoid 
muscles,  respiration  is  entirely  interrupted. 

The  Extrinsic  Muscles  are  those  of  the  anterior  region  of  the 
neck ;  those  in  the  suprahyoid  as  well  as  those  in  the  subhyoid  region. 
By  the  action  of  these  muscles  the  entire  larynx  is  moved  upward 
and  downward. 

The  Cavity  of  the  larynx  is  lined  with  a  mucous  membrane. 
The  mucous  membrane  is  continuous  with  that  of  the  trachea.  It  is 
covered  with  the  prisnuitic  or  ciliated  epithelium  in  all  places  ex- 
cept over  the  vocal  cords  and  epiglottis.  In  these  special  areas  it  is 
stratified. 

The  Vocal  Cords  comprise  two  sets,  as  was  previously  men- 
tioned; the  upi)er,  false  cords,  composed  of  folds  of  mucous  mem- 
brane, take  no  part  in  voice  production;  the  lower,  true  cords,  are 
composed  of  a  mucous  membrane  with  pavement  epithelium,  a  lamina 
of  elastic  fibers,  and  the  thyro-arytenoid  muscle. 

Opening  the  cavity  of  the  pharynx  and  raising  the  epiglottis,  the 
whole  extent  of  the  glottis  is  seen;  that  is,  the  slit  left  by  the  two 
superior  cords.  This  has  the  shape  of  a  much  elongated  triangle — 
apex  in  front,  base  at  the  back.  The  limited  anterior  part  of  the 
triangle  is  called  the  vocal  part  of  the  glottis;  whereas  the  posterior 
part  is  called  the  respiratory  portion.  It  does  not  participate  in 
phonation,  but  only  in  the  passage  of  air. 

Xerve-supply.- — The  nerves  which  are  distributed  to  the  larynx 
come  from  the  pneumogastric.  The  superior  laryngeal  nerve  supplies 
the  mucous  membrane  of  the  larynx  and  gives  the  external  laryngeal 
branch  to  the  crico-thyroid  muscle.  The  inferior,  or  rerurrenf,  laryn- 
geal nerve  supplies  allof  the  muscles  except  the  crico-thyroid.  The 
ganglia  which  preside  over  the  motor  innervation  of  the  larynx  are 
seated  in  the  floor  of  the  fourth  ventricle. 

Laryngoscopy. — The  laryngoscope  is  an  instrument  used  to 
bring  to  view  various  parts  of  the  pharynx,  larynx,  and  trachea.  It 
comprises  a  small  mirror  fastened  to  a  long  handle.  The  angle  that 
the  mirror  makes  with  its  handle  is  from  125  to  130  degrees. 

Condition  of  the  Vocal  Cords. — By  observations  made  with 
the  laryngoscope  it  has  been  determined  that,  while  in  respiration 
the  vocal  cords  are  inclined  from  each  other,  and  the  glottis  is  wide 
open,  in  speaking  or  vocalization  the  cords  are  seen  to  approximate 
and  vibrate.     In  ordinary  quiet  breathing  there  is  a  wide,  triangular- 


VOICE  AND  SPEECH. 


497 


shaped  opening  in  the  glottis.  On  the  other  hand,  during  the  pro- 
duction of  vocal  sounds  the  triangular  posterior  opening  is  com- 
pletely closed,  while  the  anterior  portion  of  the  rima  glottidis 
becomes  a  very  fine  fissure,  or  slit. 


Fig.   212. — The  Posterior  Rhinoscopic  Image.      (Bosworth.) 


VOICE. 

It  is  the  vibration  of  the  edges  of  this  fissure  by  the  passage  of 
air  through  it  that  produces  sound:  the  voice.  The  air  expelled 
from  the  lungs  acquires  a  maximum  of  tension  in  the  narrow  tracheal 
tube,  causing  it  to  strike  under  the  true  vocal  cords  and  put  them 
into  the  proper  vibrations.  But  the  tone  produced  will  not  always 
be  of  the  same  calil)er  and  height,  since  the  expired  air  may  find  the 
vocal  cords  in  different  states,  the  result  of  muscular  contractions. 

The  Height  of  the  sound  produced  in  the  larynx  depends  upon 
the  number  of  vibrations  of  the  vocal  cords  during  a  given  time. 

32 


498  PHYSIOLOGY. 

The  number  of  vihralions  would  then  depend  upon  the  slate  of  tension 
and  the  length  of  the  cords  themselves.  The  greater  the  number  of 
vibrations  during  a  second,  the  higher  will  be  the  tone,  and  vice  versa. 

The  range  of  the  human  voice,  as  regards  height,  is  usually 
between  87  and  768  vibrations  per  second.  Not  all  persons  have 
such  a  range.  Each  type  of  voice  includes  about  two  octaves.  When 
a  man  speaks — that  is,  when  he  uses  the  articulate  voice — his  voice 
does  not  exceed  the  height  of  a  half-octave.  When  he  sings,  his 
vocal  range  is  more  extended. 

The  Intensity  of  sound  depends  upon  the  extent  of  the  vibra- 
tions of  the  vocal  cords,  produced  especially  by  the  force  of  the  cur- 
rent of  air. 

The  height  of  the  voice  depends,  to  a  considerable  extent,  upon 
different  lengths  of  the  vocal  cords.     The  result  is  that  in  adult  man 


Fig.  21.3. — Position  of  Vocal  Cords  on  Uttering  a  High  Note. 
(Landois.) 

the  hass,  haritone,  and  tetior  voices  are  found,  because  of  the  greater 
length  of  the  vocal  cords  in  man.  On  the  contrary,  the  contralto, 
mezzosoprano,  and  soprano  voices  belong  to  women  and  boys,  for  they 
have  cords  shorter  in  length. 

Timbre  of  sound  depends  upon  the  nature  of  the  vibrating  body 
and  of  the  other  parts  vibrating  at  the  same  time  with  it  for  the 
production  of  harmonious  sounds. 

Resonance. — The  normal  voice  of  man  is  sonorous;  that  is,  it 
is  composed  of  vibrations  regular  in  extent  and  isochronous.  Its 
resonance  comes  either  from  the  air-tnhe  or  from  the  resonators.  By 
the  former  is  understood  the  trachea,  bronchi,  walls  of  the  lungs,  and 
thoracic  case;  by  the  latter,  the  ventricles,  pharynx,  mouth,  and 
nasal  cavities.  The  resonance  within  the  thorax  in  an  adult  causes 
a  fremitus  of  the  thoracic  wall.  This  is  greatly  increased  in  low 
sounds  and  diminishes  until  it  disappears  in  high  sounds. 

Ordinarily,  in  speaking  and  singing,  the  air  put  in  vibration  in 
the  larynx  issues  from  the  mouth  while  the  nostrils  are  open.     If 


VOICE  AND  SPEECH.  499 

they  be  closed,  the  air  which  is  held  ther©  vibrates  with  the  air 
issuing  through  the  oral  cavity  and  gives  the  voice  a  nasal  tone. 

The  human  voice  can  assume  two  different  registers.  The  one 
is  strgng  and  sonorous  and  accompanied  with  vibrations  of  the 
thoracic  wall  (chest-voice).  The  other  is  Aveak,  without  resonance, 
and  of  higher  pitch  (head-voice,  or  falsetto). 

Ventriloquy,  which  by  practice  can  reach  great  perfection,  con- 
sists only  in  the  possibility  of  changing  the  register  of  the  voice. 
The  name  derived  its  origin  from  the  erroneous  interpretation  of  it 
by  the  ancients.  They  claimed  that  the  ventriloquists  spoke  from 
the  stomach.  The  performer  is  able  to  conduct  dialogues  in  which 
two  persons  appear  to  take  part. 

Speech. — If  man  had  the  faculty  of  making  only  sounds  with 
the  larynx,  his  vocal  organ  would  not  differ  greatly  from  ordinary 
musical  instruments.  The  voice  in  such  a  case  would  but  serve  to 
make  others  aware  of  his  presence  and  to  call  them  for  the  various 
wants  of  life,  just  as  happens  in  animals  and  in  the  child  itself  when 
just  born. 

But  man  is  endowed  with  an  important  means  by  which  he  can 
communicate  to  his  fellows  the  state  of  his  mind.  It  forms  one  of 
man's  noblest  characteristics,  a  distinctive  one. 

The  infant  at  first  expresses  the  state  of  his  mind  by  cries 
accompanied  by  gestures.  Then  little  by  little  it  learns  and  tries  to 
imitate  those  sounds  which  the  parents  always  make  corresponding 
to  given  objects  and  persons.  It  pronounces  them  without  under- 
standing their  meaning.  In  later  years  it  learns  of  the  correspon- 
dence of  given  sounds  to  given  objects  and  ideas. 

Speech  is  articulate  voice.  It  is  an  ensemble  of  sounds  and 
noises  harmonized  by  the  will  and  co-ordinated  by  a  particular  cor- 
tico-motor  nervous  center.  Its  aim  is  to  make  known  to  the  listener 
the  present  state  of  mind  of  the  speaker  as  well  as  recollections  of 
the  past  and  tendencies  toward  the  future. 

Vowels  and  Coxsoxaxts. — Speech  is  composed  of  two  ele- 
ments, namely:  vowels  and  consotiants.  The  former  consist  of 
sounds  generated  in  the  larynx  and  slightly  modified  in  the  pharynx 
and  mouth-cavity.  The  consonants  result  from  noises  variously  pro- 
duced by  the  obstacles  encountered  by  the  air  in  its  passage  through 
the  pharynx  and  mouth-cavity.  Vowels  are  produced  in  the  larynx, 
pharynx,  and  mouth ;  consonants  not  in  the  larynx,  but  in  the  mouth. 

The  vowels  are  produced  by  the  different  form  of  the  cavity  of 
the  pharynx  and  mouth  during  the  expiration  of  air  through  them. 


500  PHYSIOLOGY. 

The  principal  change  in  form  consists  in  the  lengthening  and  short- 
ening of  the  mouth.     The  vowels  are  a,  e,  i,  o,  and  u. 

The  consonants  consist  of  sounds  emitted  by  the  larynx,  but 
which  become  noises  by  reason  of  obstacles  they  encounter.  Accord- 
ing to  the  obstructions  met  with,  consonants  are  termed  (jutterals 
{It,  k,  q),  Unguals  {c,  d,  g,  t,  s,  n,  I,  r),  and  labials  {b,  f,  m,  p,  v).  The 
Unguals  are  subdivided  into  palatals  and  dentals. 

The  very  varied  union  of  the  vowels  with  the  consonants  con- 
stitutes syllables;   union  of  the  latter  forms  words. 

Stammering  is  due  to  a  continued  spasmodic  contraction  of  the 
diaphragm  and  to  the  muscles  of  the  larynx  not  harmonizing  the 
chink  of  the  glottis. 

Stuttering  is  due  to  a  want  of  ability  to  form  the  proper  sounds 
by  the  laryngeal  muscles;  the  breathing  and  diaphragm  are  both 
normal. 

Pathology. — Paralysis  of  the  motor  nerves  of  the  larynx  from 
the  pressure  of  tumors,  causes  aphonia,  or  loss  of  voice.  In  aneur- 
ism of  the  aortic  arch  the  left  recurrent  nerve  may  be  paralyzed  from 
pressure.  The  laryngeal  nerves  may  be  temporarily  paralyzed  by 
overexertion  and  hysteria. 

If  one  vocal  cord  be  paralyzed,  the  voice  is  not  pure  in  tone,  but 
falsettolike. 

Hoarseness  may  be  caused  by  mucus  upon  the  vocal  cords  or  by 
roughness  or  laxness  of  the  cords.  Disease  of  the  pharynx  or  naso- 
pharynx and  uvula  may,  in  a  reflex  manner,  produce  a  change  in  the 
voice. 

APHASIA. 

Aphasia  means  a  loss  of  power  to  produce  or  understand  spoken 
or  written  speech. 

Aphasia  is  a  disorder  of  the  speech,  due  to  a  lesion  of  the  third 
left  frontal  convolution.  There  are  four  different  kinds  of  word- 
memory,  each  having  its  seat  of  registration  in  a  well-defined  part 
of  the  cortex.  The  first  is  the  (1)  auditory  word-center,  where  the 
sound  of  words  is  registered;  (3)  a  visual  word-center,  where  the 
visual  images  of  letters  and  words  are  registered ;  (3)  a  glosso-kinaes- 
thetic  center,  where  the  combined  impressions  which  pass  to  the 
brain  as  a  result  of  the  movements  of  the  lips,  tongue,  palate,  larynx, 
and  other  parts  concerned  in  articulate  speech,  are  registered;  (4) 
a  cheiro-kinaesthetic  center,  where  sensory  impressions  resulting  from 
the  movements  made  in  writing  are  stored  up.     From  the  glosso- 


VOICE  AND  SPEECH.  501 

kingestbetic  and  cheiro-kinaesthetic  center,  fibers  descend  as  part  of 
the  pyramidal  motor  tract,  those  from  the  glosso-kina^sthetic  center 
going  to  the  motor-speech  apparatus  in  the  medulla,  and  those  from 
the  cheiro-kinEBsthetic  center  going  to  the  spinal-motor  ganglia  con- 
cerned in  the  act  of  writing.  As  is  known,  the  auditory  word-center 
is  in  the  first  temporal  convolution,  the  visual  word-center  in  the 
gyrus  angularis  and  a  part  of  the  supramarginal  gyrus,  the  speech- 
center  in  the  third  left  frontal  convolution,  and  the  writing  center 
in  the  posterior  part  of  the  second  frontal  convolution. 

The  auditory  word-center  is  the  first  called  into  activity;  then 
the  speech-center  is  gradually  organized  under  the  influence  of 
excitations  coming  from  the  auditory  word-center.  After  a  year  or 
two  the  child's  visual  word-center  becomes  organized,  and  the  child 
recognizes  letters  and  words,  and  at  the  same  time  two  sets  of  asso- 
ciation-channels, commissural  fibers,  are  laid  down  between  the  audi- 
tory word-center  and  this  visual  word-center.  Finally,  the  child 
reads;  then  there  must  be  activity  first  in  the  visual  word-center, 
then  in  the  auditory  word-center,  and  immediately  afterwards  in  the 
glosso-kingesthetic  center.  Then,  as  the  child  learns  to  write,  the 
cheiro-kingesthetic  center  becomes  organized,  the  guiding  influence 
of  the  visual  center  being  called  into  play,  and  this  would  lead  to  a 
development  of  commissural  channels  between  the  two  centers.  The 
visual  center  holds  the  same  sort  of  relation  to  the  act  of  writing 
that  the  auditory  word-center  holds  to  articulate  speech.  In  writing 
from  dictation,  the  train  of  activity  starts  in  the  hearing  word-cen- 
ter, spreads  to  the  visual  word-center,  thence  to  the  cheiro-kinaes- 
thetic center,  where  the  efferent  stimuli  pass  over  to  the  spinal  motor 
centers     (Bastian,  Allbutt's  System  of  Medicine,  vol.  VIII). 

The  chief  varieties  of  aphasia  are: — 

,      .        {  aphemia. 
Motor  aphasia     <  ,  . 

'■  I  agraphia. 

T     •     f  visual. 
Sensory  aphasia  <        ... 

-'     ^  I  auditory. 

Conduction  aphasia.     ■ 

Auditory  Aphasia. — Supposing  the  patient's  hearing  is  perfect, 
then  auditory  aphasia  is  revealed  by  his  inability  to  put  out  his 
tongue. 

Visual  Aphasia  (Alexia). — Supposing  the  patient  can  see  per- 
fectly, can  the  patient  understand  written  or  printed  words  ?  If  he 
'fails  to  do  so,  he  has  alexia. 


502  PHYSIOLOGY. 

Motor  Aphasia  (Aphemia). — 11'  he  can  speak  voluntarily,  can  he 
repeat  words  or  read  aloud?     If  he  cannot,  he  has  aphemia. 

Agraphia. — Supposing  the  patient  can  write  voluntarily,  can  ho 
write  from  dictation  or  from  copy?     If  he  cannot,  he  has  agraphia. 

A  symptom  found  in  all  cases  of  aphasia:  if  he  cannot  write 
voluntarily,  because  of  inability  to  remember  words,  but  can  write 
from  dictation,  it  is  sensory  agraphia.  If  he  cannot  write  either 
voluntarily  or  from  dictation,  it  is  motor  agraphia. 

If  he  uses  one  word  for  another,  so  that  the  result  is  unintelli- 
gible, then  there  is  paraphasia. 

If  he  writes,  and  he  uses  one  word  for  another,  so  that  it  is 
unintelligible,  then  para-agraphia. 

Paraphasia  and  paragraphia  are  symptoms  of  conduction  apha- 
sia, lesion  of  commissural  fibers,  and  the  lesion  is  ordinarily  in  the 
island  of  Reil  or  the  convolutions  about  the  fissure  of  Sylvius. 

Motor  Aphasia. — If  the  patient  can  read  silently,  write  volun- 
tarily, write  from  dictation,  copy  and  hear  and  understand  spoken 
words,  but  cannot  speak  voluntarily,  repeat  words  or  read  aloud,  then 
the  lesion  is  in  Broca's  convolution,  tliird  frontal  (motor  apliasia. 
aphemia). 

If  the  patient  can  hear  and  understand  spoken  words,  read  and 
understand  written  or  printed  words  and  copy,  but  cannot  speak  vol- 
untarily, repeat  words,  read  aloud,  write  voluntarily  or  from  dicta- 
tion (aphemia  plus  agraphia),  there  is  a  lesion  of  the  third  left  frontal 
convolution.     This  is  the  most  frequent  form  of  aphasia. 

Visual  Aphasia. — If  the  patient  can  speak  voluntarily  and  under- 
stand spoken  words,  but  cannot  understand  written  or  printed  words, 
write  voluntarily  or  from  dictation  or  from  copy  (visual  aphasia  plus 
agraphia),  there  is  a  lesion  in  the  angular  gyrus  and  supramarginal 
lobe. 

Auditory  Aphasia. — If  the  patient  can  speak  voluntarily,  read 
intelligently,  and  write  voluntarily,  but  cannot  understand  spoken 
words,  repeat  words  or  write  from  dictation  (auditory  aphasia),  then 
there  is  a  small  subcortical  lesion  of  the  first  and  second  temporal 
convolutions.     (Butler's  Diagnostics). 


CHAPTER  XIII. 

ELECTRO=PHYSIOLOQY. 

ELECTRICITY. 

Electrical  Measurements. 

The  system  of  electrical  measurements  now  in  use  is  founded  on 
the  centimeter  as  the  unit  of  length,  the  gramme  as  the  unit  of  mass, 
and  the  mean  solar  second  as  the  unit  of  time.  This  is  commonly 
designated  as  the  C.  G.  S,  system. 

The  amiDere  is  the  unit  of  current;  the  unit  of  electromotive 
force,  the  volt;   the  unit  of  resistance,  the  ohm. 

The  ampere  is  equal  to  one-tenth  of  the  C.  G.  S.  unit  of  cur- 
rent, or  approximately  the  current  of  an  ordinary  Daniell  cell  through 
an  ohm.  The  volt  is  100,000.000  times  the  C.  G.  S.  unit  of  electro- 
motor force,  or  approximately  the  electromotive  force  of  a  Daniell 
cell.  The  ohm  is  the  resistance  of  a  column  of  pure  mercury  1 
millimeter  square  and  1063  millimeters  in  length,  at  zero  degrees  C. 

To  Measure  Work. — ^To  measure  work  of  contracting  muscle,  the 
millimeter-gramme  is  the  unit  in  the  metrical  system  as  that  work 
required  to  overcome  a  force  equal  in  weight  of  one  gramme  acting 
through  the  space  of  one  millimeter. 

Cells  or  Batteries. — 1.  Daniell  Cell. — The  first  constructed  con- 
stant battery.  It  consists  of  a  glass  jar  filled  with  concentrated  solu- 
tion of  snlphate  of  copper,  bathing  an  unclosed  ring  of  sheet  copper 
around  a  porous  earthen  jar  filled  with  sulphuric  acid  (1  to  10  of 
water),  in  which  is  immersed  a  rod  of  zinc.  The  zinc  pole  is  the 
negative  or  the  cathode,  and  the  copper  pole  the  positive  or  the  anode, 
and  its  electromotive  force  (E.  M.  F.)  is  about  1.07  volts.  On  ac- 
count of  the  constancy  of  the  battery  it  is  the  one  chiefly  used  in 
laboratories  of  physiology. 

2.  Dry  Cells. — The  Just-described  wet  cell  gives  off  fumes, 
contains  acids,  and  must  be  prepared  for  use.  As  the  dry  cell  is 
always  ready  and  without  the  preceding  disadvantages,  it  is  used 
extensively  in  the  laboratory.  The  dry  cells  are  usually  modified 
Leclanche  batteries.  The  Leclanche  cell  consists  of  a  glass  jar  con- 
taining a  saturated  solution  of  ammonium  chloride,  into  which  an 
amalgamated  zinc  rod  dips.  The  zinc  is  negative  and  the  carbon 
positive.    The  plate  of  carbon  is  fitted  into  a  porous  pot  packed  with 

(503) 


504 


PHYSIOLOGY. 


pieces  of  carbon  and  dioxide  of  manganese.  Its  electromotive  force 
is  1.5  volts,  'llie  dry  cell  is  usually  made  of  a  zinc  cup  lined  with 
plaster  of  Paris,  saturated  with  amomnium  chloride.  A  carbon  plate 
is  placed  in  the  center  of  tliis  and  surrounded  with  black  oxide  of 
manganese. 

Polarization  of  Plates. — The  voltaic  battery  consists  of  two 
metals,  zinc  and  copper,  which  are  surrounded  by  an  electrolyte  con- 
taining various  ions.  The  positive  ions,  Cu  and  H,  will  work  their 
way  towards  the  positive  element,  the  copper  plate,  and  the  OH  and 
SO4,  being  negative  ions,  will  go  towards  the  zinc.  The  hydrogen 
gas  settles  in  minute  bubbles  upon  the  surface  of  the  copper  plate  and 


^K 


Fig.  214.— Daniell  Cell. 

at  once  interferes  with  the  action  of  the  battery.  It  interferes  both 
by  the  resistance  it  offers  to  the  passage  of  the  current,  and  also  by 
setting  up  a  current  in  an  opposite  direction,  which  tends  to  weaken 
the  original  current  by  neutralization.  This  action  is  called  polari- 
zation of  the  plates.  Besides  this,  in  such  an  element  some  of  the 
sulphate  of  zinc  produced  in  the  element  is  attacked  by  the  hydrogen 
and  deposited  on  the  copper  plate,  so  that  the  copper  plate  begins  to 
approach  the  condition  of  the  zinc  plate,  and,  of  course,  the  difference 
of  potential  or  electromotive  force  is  reduced.  In  all  these  ways  the 
current  is  diminished  and  the  cell  is  not  of  constant  strength. 

Polarization  in  the  Daniell  cell  is  overcome  by  the  solution  of 
copper  sulphate,  and  in  the  Leclanche  cell  by  the  manganese  dioxide. 

Resistances. — There  are  two  kinds  of  resistance  to  electric  cur- 
rents:   Internal  resistance  or  the  resistance  of  the  element,  or  the 


ELECTRO-PHYSIOLOGY.  505 

resistance  the  current  experiences  in  passing  through  the  liquid  of  the 
cell  from  one  plate  to  another;  and  external  resistance,  or  the  resist- 
ance the  current  meets  with  in  passing  through  the  electrodes  and 
apparatus.  Internal  resistance  is  inversely  proportional  to  the  size 
of  the  cell,  and  directly  proportional  to  their  distance  from  one 
another;  that  is,  the  larger  the  plate  the  less  the  resistance,  and  the 
greater  the  distance  the  greater  the  resistance,  the  conducting  power 
of  the  liquid  being  always  the  same.  External  resistance  depends 
on  the  conductivity  of  the  conductor,  which  is  a  constant  quantity  for 
each  conductor.  External  resistance  is  directly  proportional  to  the 
length  of  the  conductor  and  inversely  proportional  to  the  cross-sec- 
tion ;  that  is,  the  longer  the  conductor  the  greater  the  resistance,  and 
the  thicker  the  (wire)  conductor  the  less  the  resistance.  The  thinner 
the  wire  the  greater  is  the  resistance. 

Batteries  may  be  united  together  as  positive  pole  to  negative 
pole.  Here  the  voltage  is  equal  to  the  voltage  of  a  single  cell  multi- 
plied by  the  number  of  cells.  This  method  of  coupling  is  used  in  the 
medical  battery  for  the  application  of  the  galvanic  or  constant  cur- 
rent to  man.  Another  method  is  to  couple  abreast  or  "in  multiple 
arc."  Here  the  positive  poles  are  on  one  wire  and  the  negative  on 
another  wire.  Here  we  have,  as  a  matter  of  fact,  a  single  cell  with 
plates  as  many  times  larger  as  we  have  taken  cells.  The  electromotive 
force  is  not  altered,  since  the  electromotive  force  of  a  cell  varies  with 
its  chemical  constituents  and  not  with  the  size  of  the  cell.  Now,  the 
internal  resistance  of  a  cell  is  inversely  proportional  to  the  size  of  the 
plates,  so  that  by  multiplying  the  size  of  the  plates  by  the  number  of 
cells,  say  six,  then  the  internal  resistance  is  practically  diminished 
one-sixth.     Increased  quantity  of  current  is,  therefore,  obtained. 

The  human  body  opposes  to  the  electric  current  so  great  an 
external  resistance  that  the  internal  resistance  of  the  battery  can  be 
overlooked;  hence  surface  extent  of  the  zincs  can  be  neglected.  The 
intensity  of  the  current  is  determined  by  the  number  of  the  elements 
and  not  by  their  size,  hence  you  couple  in  series.  When,  however, 
you  employ  electricity  to  heat  the  galvano-cautery  wire,  which  is 
short  and  of  feeble  external  resistance,  you  augment  the  intensity  of 
the  current  by  increasing  the  surface  (size)  of  the  zincs.  It  is  true 
you  do  not  augment  the  electromotive  force;  but  as  the  resistances 
diminish  in  proportion  to  the  increase  of  size  of  the  zinc,  the  inten- 
sity of  the  current  increases  in  proportion  to  the  increase  of  size  of  the 
zincs.    You  can  have  an  apparatus  to  heat  the  cautery  wire  by  coup- 


506  PHYSIOLOGY. 

ling  cells  abreast  or  in  multiple  arc,  which  amounts  to  the  same  thing 
as  having  a  cell  with  large-sized  zincs. 

To  summarize :  to  obtain  increased  intensity  of  current  with 
small  external  resistance,  as  in  a  cautery  wire,  either  use  large  cells 
or  couple  a  number  of  cells  abreast  or  in  multiple  are;  with  great 
external  resistance,  as  in  the  application  of  the  galvanic  current  to  the 
human  body  or  the  nerves  of  an  animal,  you  couple  the  cells  in  series, 
small  elements  being  as  good  as  large.  One  centimeter  of  nerve  offers 
a  resistance  of  about  80,000  ohms  and  nonpolarizable  electrodes  have 
a  resistance  equal  to  700  ohms  each. 

Ohm's  Law. — G.  S.  Ohm,  in  1827,  formulated  a  law : — 
Current  strength  (amperes)   C.  = 

E.  M.  F.  =  Electromotive  force  (volts). 
H       =Eesistance   (ohms). 

But,  there  are  two  resistances,  so  let  E  stand  for  internal  resist- 
ance and  r  for  external  resistance ;  the  law  will  be 

E.  M.  F. 


C 


R  +  r 

The  ohm,  the  ampere,  and  the  volt  are  closely  related,  and  if 
any  two  of  them  are  known  with  reference  to  any  particular  electric 
current,  the  value  of  the  third  may  be  readily  inferred. 

Currents  are  measured  in  amperes,  resistances  in  ohms. 
Electromotive  force  is  the  force  which  tends  to  move  electricity 
from  a  higher  to  a  lower  potential.     The  unit  of  electromotive  force 
is  the  volt,  and,  therefore,  is  the  measure  of  electrical  pressure. 

Electromotive  force  is  "difference  in  potential."     A  volt  is  that 
amount  of  electrical  energy  which  will  produce  one  ampere  of  current 
after  overcoming  one  ohm  of  resistance. 
Then  :— 

Volts  =   amperes  X  ohms. 
Amperes  =  volts  -^  ohms. 
Ohms  =  volts  -^-  amperes. 

The  small  Daniell  cell  has  4  ohms  resistance  and  a  current  of 
^/^  ampere. 

"The  difference  of  potential  may  be  compared  to  the  difference 
of  water-level  between  a  reservoir  and  its  distributing  pipes.  It  pro- 
duces an  electromotive  force  comparable  to  the  force  which  moves 
the  water  from  a  higher  to  a  lower  level.  The  unit  of  electrical  pres- 
sure is  the  volt.     The  flow  through  a  hydraulic  system  is  measured 


ELECTRO-PHYSIOLOGY.  507 

by  the  quantity  of  water  passing  any  point  in  a  given  time ;  similarly, 
the  quantity  of  electricity  is  the  amount  that  iiows  through  a  cross- 
section  of  the  conductor  in  a  given  time.  The  unit  of  quantity  is 
the  ampere."  Eoughly  speaking,  your  bladder  filled  with  urine  may 
be  a  volt,  the  ohm  may  be  a  stricture,  and  an  ampere  the  passing 
stream  of  urine  or  the  unit  of  measure  of  the  amount  of  urine  pass- 
ing through  an  object  in  a  second  of  time. 

Electrodes. — To  carry  the  current  from  the  different  metals  or 
carbons  we  have  wires  covered  with  cotton,  or  silk,  or  gutta-percha, 
which  are  attached  to  the  metals  or  carbon;  they  are  then  called 
electrodes. 

Polarization  of  Electrodes. — In  electrolysis  of  the  lymph  by  the 
current  in  a  tissue  there  are  produced  positive  and  negative  ions  in 
the  lymph,  which  act  on  the  electrodes.     If  a  pair  of  clean  platinum- 


Fig.  215. — DuBois  Xonpolarizable  Electrodes.      (Lahousse.  ) 

wire  electrodes  have  been  immersed  in  water  and  have  been  convey- 
ing a  current  for  decomposition,  the  positive  pole  will,  after  some 
time,  become  covered  with  bubbles  of  oxygen,  while  the  negative  will 
have  collected  on  it  hydrogen  gas.  If  now  these  electrodes  be  sud- 
denly disconnected  with  the  battery  and  connected  with  a  galvano- 
meter, the  needle  of  the  galvanometer  will  deviate  in  such  a  way  as 
to  show  a  current  in  an  opposite  direction  to  the  original  battery 
current.  This  is  caused  by  the  coating  of  the  negative  pole  with 
hydrogen,  making  it  positive,  and  a  current  runs  from  the  electrode 
covered  with  hydrogen  to  the  electrode  covered  with  oxygen;  that 
is,  it  runs  in  an  opposite  direction  to  the  original  current  when  the 
battery  was  attached  to  the  electrodes.  This  current  will  naturally 
weaken  the  original  battery  current.  This  occurrence  is  called 
polarization  of  electrodes.  In  the  same  way,  if  a  fresh  muscle  or 
nerve  be  laid  across  two  copper  wires  carrying  a  battery  current,  and 
these  be  connected  with  a  galvanometer  (previously  disconnecting  the 


508  PHYSIOLOGY. 

battery),  a  deviation  of  the  galvaiiometer-neeclle  will  be  apparent, 
showing  a  reversal  of  direction  of  current,  as  was  the  case  with  the 
electrodes  in  water.  To  get  rid  of  this  current,  due  to  polarization 
of  the  electrodes  by  the  tissue  of  the  muscle  or  nerve,  it  was  neces- 
sary to  employ  electrodes  which  were  unpolarizable.  Eegnault  found 
these  to  be  zinc  immersed  in  a  strong  solution  of  zinc  sulphate. 
DuBois-Reymond  constructed  electrodes  upon  this  plan.  They  are 
usually  made  by  taking  two  small  pieces  of  glass  tubing,  open  at  both 


Fig.  216. — Tetanizing  Key  of  DuBois-Reymond.  (After  Rosen- 
thal.) (From  Mills's  "Animal  Physiology,"  copyright,  1889,  by  D. 
Appleton  and  Company. ) 

Wires  may  be  attached  at  6  and  c.  When  d  is  down  the  current  is  "short- 
circuited,"  i.e.,  does  not  pass  through  the  wires,  but  direct  from  c  through  il  to 
6,  or  the  reverse,  since  b,  c,  d  are  of  metal  and,  on  account  of  their  greater 
cross-section,  conduct  so  much  more  readily  than  the  wires,  a  Is  an  insulating 
plate  of  ebonite.     This  form  of  key  is  adapted  for  attachment  to  a  table,  etc. 

ends  and  curved.  One  end  of  the  tube  is  plugged  with  modeling 
clay,  moistened  with  salt  solution,  and  then  the  tube  is  filled  with  a 
saturated  solution  of  sulphate  of  zinc  in  which  is  immersed  a  rod  of 
amalgamated  zinc  and  to  which  one  of  the  wires  of  the  circuit  is 
attached.  The  non-polarizable  electrodes  of  Porter's  are  porous, 
boot-shaped  cups  filled  with  saturated  solution  of  sulphate  of  zinc, 
in  which  is  plunged  a  zinc  rod. 

After  the  use  of  the  unpolarizable  electrodes  the  boot  should  be 


ELECTRO-PHYSIOLOGY.  509 

emptied,  rinsed  in  tap  water,  cleaned,  and  placed  in  several  hundred 
cubic  centimeters  of  normal  saline  until  wanted.  If  the  boot  is  kept 
saturated  with  normal  saline,  the  electrodes  will  remain  non-poiar- 
izable. 

Detector,  or  Galvanoscope,  or  Current  Indicator. — Use  a  vertical 
galvanoscope,  in  which  the  magnetic  needle  is  so  loaded  as  to  rest 
in  a  vertical  position.  It  consists  of  a  magnetized  needle,  sur- 
mounted by  a  coil  of  wire.  It  indicates  the  passage  and  direction 
of  a  current.  It  really  is  a  little  galvanometer.  Xow,  connect  the 
wires  from  the  positive  (+)  and  negative  ( — )  poles  of  a  battery  with 
the  binding  screws,  and  note,  when  the  circuit  is  closed,  the  needle 
deviates  from  its  vertical  poRitinn. 


Fig.   217. — Polil's   Commutator.      (Lahousse.) 

Keys. — When  we  wish  to  make  or  break  a  current  by  hand  we 
use  keys.  DuBois  key  consists  of  two  metal  blocks,  each  carrying 
two  binding-screws  fitted  on  a  base  of  hard  rubber,  which  acts  as  an 
insulator.  These  two  blocks  of  metal  are  connected  by  a  metal 
cross-bar  which  thus  closes  the  key.  It  is  employed  in  two  ways. 
In  one,  it  breaks  the  current  going  from  the  cell  to  the  nerve ;  when 
the  key  is  closed  the  current  is  made,  when  the  key  is  open  the  cur- 
rent is  broken.  In  the  other  way,  the  current  from  the  cell  passes 
through  the  key  when  it  is  closed  and  then  it  is  a  short-circuiting 
key,  because  the  current  going  through  the  electrodes  from  the  short- 
circuiting  key  to  the  nerve  meets  here  a  body  (the  nerve)  which 
opposes  a  great  resistance  to  the  passage  of  the  electrical  current, 
and,  as  electricity  always  takes  the  easiest  way  home,  it  goes  through 


510  PIIYSIOLOGY. 

the  conductor  offering  the  smaller  resistance,  the  brass  key.  If  the 
key  is  open,  then  the  whole  current  pa&ses  to  the  nerve.  This 
method  of  using  the  key  is  known  as  "short-circuiting.^'  In  using 
the  key  to  apply  an  induction  or  Faradic  current  to  excite  a  nerve  or 
muscle,  always  use  this  method ;  that  is,  place  a  short-circuiting 
key  in  the  secondary  circuit  to  prevent  unipolar  action. 

Mercury  Key. — Where  a  fluid  contact  is  required  the  wires  dip 
into  the  mercury.  It  is  used  in  the  same  way  as  the  DuBois  key, 
for  nuike-and-brcak  shocks. 

Commutators.- — PohTs  commutator  is  used  for  sending  (1)  a  cur- 
rent into  two  different  pairs  of  wires;  (2)  for  reversing  the  direc- 
tion of  the  current  in  a  pair  of  wires;  (3)  it  can  also  be  used  as  a 
mercury  key.  It  consist  of  a  round  block  of  wood  with  six  cups, 
each  containing  a  binding-screw.  Between  two  of  these  stretches  is  a 
bridge  insulated  in  the  middle.  The  battery  is  attached  to  the  lead- 
ing-in  wires,  and,  as  the  bridge  is  rocked  from  one  side  to  the  other, 
the  current  is  sent  through  one  or  the  other  pair  of  wires.  To 
reverse  the  direction  of  a  current,  only  one  pair  of  leading-out  wires, 
besides  the  cell  wires,  is  attached  to  the  binding-screws  of  the  mer- 
cury cups.  Then  the  cross  bars  are  inserted,  which  change  the  direc- 
tion of  the  current  on  rocking  the  bridge. 

Induction  or  Faradic  Currents. 

DuBois-Reymond's  Induction  Apparatus. — It  consists  of  a  pri- 
mary spiral  of  aljout  130  coils  of  a  moderately  thick  silk-covered 
copper  wire,  and  of  a  secondary  spiral  of  some  6000  coils  of  silk- 
covered  copper  wire  of  a  thickness  of  about  a  tenth  of  a  millimeter. 
The  core  inside  the  primary  spiral  is  formed  by  a  bundle  of  thin 
iron  wires,  each  carefully  coated  with  shellac  varnish.  To  graduate 
the  strength  of  the  induced  current  of  the  secondary  spiral,  the  sec- 
ondary spiral  is  moved  in  a  groove  of  w^ood  from  or  towards  the  pri- 
mary spiral,  and  the  distance  between  the  spirals  is  graduated  in 
centimeters  and  millimeters,  or  the  secondary  spiral  is  rotated  as  by 
Bowditch.  To  make  or  close,  or  to  break  or  open  the  circuit 
coming  from  the  cell  through  the  primary  spiral,  the  electro- 
magnetic hammer  of  iSTeef  is  used  to  give  us  repeated  shocks, 
or  the  interrupted  current.  When  single  induction  shocks  are 
used,  the  wires  from  the  battery  are  connected  with  a  key 
and  this,  again,  with  the  two  terminals  of  the  primary  spiral.  The 
action  of  the  coil  of  wires  depends  upon  the  fact  that  the  strength 
of  a  current  running  along  a  wire  will  be  altered  and  an  induced 


ELECTRO-PHYSIOLOGY. 


511 


current  set  up  in  a  second  wire  placed  near  it.  The  strength  of  the 
induced  current  may  be  increased  by  placing  a  bundle  of  soft  iron 
wires  in  the  interior  of  the  primary  coil.  By  using  a  large  number 
of  turns  of  wire  in  each  coil  the  effect  is  greatly  increased,  because 
each  turn  of  the  primary  coil  induces  a  current  in  each  of  the  turns 


Fig.  218. — DuBois-ReymoncFs  Induction  Apparatus.     (Waller.) 

The  numbers  1  to  7  indicate  the  terminals  and  contact  screws  connected  with 
the  primary  coil. 

For  single  shocks  the  two  battery  wires  are  to  be  connected  with  the  termi- 
nals 4  and  5,  which  are  at  the  two  ends  of  the  primary  wire. 

(a)  Unmodified  sJwcks  are  obtained  when  a  key  is  used  to  interrupt  one  of 
the  wiles. 

(h)  Reduced  shocks  are  obtained  when  a  key  is  used  short-circuiting  the 
primary  wire. 

(r)  For  repeated  shocks  (ordinary)  the  two  battery  wires  are  to  be  inserted 
at  1  and  6.  The  circuit  now  includes  the  spring  interrupter  and  the  wire  of 
the  electro-magnet  by  which  the  circuit  is  made  and  broken  at  the  contact 
screw  3;    the  contact  screw  7  is  kept  out  of  use  by  being  lowered. 

(d)  For  repeated  shocks  {modified)  the  battery  wires  are  left,  as  before,  at 
1  and  6.  A  short,  thick  side  wire  is  placed  between  2  and  4.  The  contact 
screw  3  is  raised  out  of  range  of  the  spring,  and  the  contact  screw  7  is  raised 
until  it  comes  within   range  of  the  spring. 

The  electrode  wires  are  in  each  case  connected  with  two  terminals  (not  seen 
in  figure)  forming  the  two  ends  of  the  secondary  wire. 


of  the  second,  and  all  these  small  effects  summed  up  produce 
a  single  greatly  increased  effect.  The  opening  shock  is  stronger 
than  the  closing  shock,  so  that  if  repeated  induction  shocks  are  sent 
through  a  tissue  for  some  time  polarization  effects  are  set  up.     To 


512  PHYSIOLOGY. 

equalize  the  shocks,  Helmholtz  used  a  modification  consisting  of  a 
"side  wire."  Helinholtz's  side-wire  and  the  modifications  it  intro- 
duces into  the  induction  apparatus  should  be  used  when  induced  cur- 
rents are  applied  to  nerves.  By  this  contrivance  we  diminish  two 
possible  mistakes:  (1)  the  undesirable  predominance  of  currents  in 
one  direction,  that  is,  in  that  of  the  break;  (2)  unipolar  stimulation. 
Helmholtz's  side-wire  acts  by  short-circuiting  instead  of  completely 
breaking  the  battery  current. 

Unipolar  Induction. — If  you  remove  one  of  the  wires  of  the 
electrodes  of  the  secondary  coil,  so  that  only  one  electrode  is  con- 
nected with  that  coil,  and  slide  the  coil  towards  the  primary  coil. 


r'ig.  219.-^— Principle  of  Simple  Rheocord. 
G,  Galvanometer.     R,  Rheocord.    P,  Battery. 

then  send  a  strong  current  through  Xeef's  hammer  and  the  primary 
coil,  shocks  will  be  faintly  felt  by  the  tongue,  though  only  one  elec- 
trode is  attached  to  the  secondary  coil.  It  is  on  account  of  this  pos- 
sibility of  stimulating  through  only  one  pole  that  a  short-circuiting 
key  is  always  used  in  the  secondary  spiral  current.  In  the  primary 
or  battery  current  a  simple  key  is  used,  for  a  short-circuiting  key 
would  let  the  battery  quickly  run  down. 

Rheocord. — A  rheocord  is  an  apparatus  for  dividing  a  constant 
current  by  offering  a  circuit  of  relatively  small  resistance,  which  is 
capable  of  being  varied  so  that  a  variable  part  only  of  the  current 
shall  pass  through  the  experimental  circuit.  It  usually  consists  of 
a  platinum  wire  of  known  resistance,  to  the  ends  of  which  the  bat- 
tery poles  are  connected.     With  one  of  these  ends  another  wire  is 


ELECTRO-PHYSIOLOGY. 


513 


connected.  This  forms  part  of  the  experimental  circuit  through 
which  a  portion  of  the  battery  current  is  to  be  conducted.  This  cur- 
rent is  completed  through  a  wire  attached  to  a  rider  which  slides 
along  the  rheocord  wire.  The  other  portion  of  the  current  goes 
through  unpolarizable  electrodes  to  a  nerve  lying  across  them.  The 
amount  of  current  passing  through  the  nerve  varies  directly  with  the 
resistance  of  the  deriving  circuit,  the  rheocord.  By  increasing  this 
resistance  more  current  is  sent  through  the  nerve,  and  on  diminish- 
ing, less. 


Fig.  220. — Schema  of  Apparatus  to  Study  Influence  of  Rapid 
Variations  of  the  Constant  Current  by  the  Rheonome  of  von  Fleischl. 
(Lahousse.) 

P,    Daniell   cells.     E,    Key.     A.    B,    Two   pieces   of   zinc   to   which   the  wires  are 
attached.     C,  D,  These  two  points  are  united  by  wires  to  the  muscle  31. 


Suppose,  for  example,  that  the  resistance  of  the  electrode  and 
nerve  is  100,000  ohms  and  the  resistance  of  the  rheocord  5  ohms, 
100,000  5 

then  77r;rrrTr  of  the  current  passes  through  the  rheocord  and  ~rZn~^Zf. 
lUU.UOo  100,005 

through  the  nerve. 

Rheonome  of  Von  Fleischl. — The  rheonome  of  Yon  Feischl  con- 
sists of  an  ebonite  plate  with  a  circular  groove  on  its  upper  surface. 
This  groove  is  connected  at  diametrically  opposite  points  to  the  bind- 
ing-screws. In  the  center  of  the  ebonite  plate  is  a  vertical  rod  whose 
upper  extremity  articulates  with  a  piece  of  ebonite,  which  is  mov- 
able and  has  on  its  two  surfaces  two  plates  of  zinc,  which  are  curved 
in  an  archlike  form.     Their  upper  extremities  are  united  to  the  bind- 

33 


514 


PTTYSTOLOCY. 


Fig.  221. — Schema  of  Experiment  to  Measure  the  Rapidity  of  the 
Muscle  Current  by  the  Aid  of  the  Differential  Rheotome  of  Bernstein. 
(Lahousse.  ) 

M,  Muscle  prepared  in  such  £,  manner  that  by  one  extremity  the  muscle 
current  goes  to  the  galvanometer,  and  to  the  other  extremity  electrodes  are 
applied  which  carry  to  the  muscle  an  induction  current.     G,   Galvanometer. 

The  rheotome  of  Bernstein  (A)  consists  essentially  of  a  disc  (B),  which  is 
set  in  uniform  and  rapid  motion  by  the  rotation  apparatus  of  Helmholtz  (H). 
At  each  revolution  the  needle  C,  striking  the  wire  C",  closes  and  opens  rapidly 
the  primary  current  of  the  induction  apparatus  in  such  a  manner  as  to  excite 
the  muscle  by  a  single  induction  current.  On  the  opposite  side  of  the  disc  lie 
two  needles  (D,  D)  which,  dipping  in  the  two  cups  of  mercury  {D',  D'),  close 
for  a  very  short  time  the  circuit  of  the  muscle  current.  If  the  rapidity  of 
rotation  of  the  disc  is  known  and  the  interval  which  elapses  between  the  time 
of  excitation  of  the  muscle,  that  is,  the  time  when  the  needle  (C)  strikes  against 
the  wire  (C),  and  the  beginning  of  the  closing  of  the  muscle  current,  that  is,  the 
time  when  the  two  needles  (D,  D)  commence  to  dip  into  the  mercury  cups 
(C,  D'),  then  the  rapidity  of  the  propagation  of  the  negative  wave  or  variation 
is  easily  calculated. 


ELECTRO-PHYSIOLOGY. 


515 


ing-screws,  and  their  lower  extremities  dip  into  the  groove  filled  with 
a  saturated  solution  of  sulphate  of  zinc.  The  arched  plates  are  called 
the  bridge.  Three  Daniell  cells  are  connected  to  the  binding-screws, 
with  the  interposition  of  a  key.  The  binding-screws  are  united  to 
electrodes  upon  which  lie  the  nerve-muscle  preparation.  When  the 
key  is  closed  the  muscle  contracts  and  in  the  interval  relaxes,  except 
when  there  is  a  rotation  of  the  bridge. 

Then  suddenly  rotate  the  handle  with  its  two  zinc  arms.  This 
is  equivalent  to  a  sudden  variation  of  the  intensity  of  the  current, 
the  current,  of  course,  continuing  to  pass  all  the  time.  The  muscle 
suddenly  contracts.     The  response  of  a  muscle  or  nerve  to  electrical 


Fig.   222. — The   Nerve-muscle  Preparation.      (Stirling.) 

S,   The  nerve-muscle.     F,   Lower  third  of  femur.     /,   Tendon  of 
gastrocnemius  muscle. 

stimulation  is  due  not  to  the  simple  flow  or  intensity  of  a  current 
through  the  tissues,  but  rather  to  the  more  or  less  sudden  change  in 
the  strength  of  the  current.  Sudden  increase  or  decrease  may  act 
as  an  efficient  stimulus,  but  the  gradual  increase  or  decrease  of  the 
current  causes  no  response  (Du  Bois's  law.) 

Differential  Rheotome. — The  rheotome  of  Bernstein  is  an  instru- 
ment by  which  a  series  of  stimuli  can  be  led  into  a  nerve  or  muscle, 
and  the  consequent  excitatory  effects  led  off  to  a  galvanometer  dur- 
ing definite  periods  at  regular  intervals  after  stimulation. 

ELECTRO-PHYSIOLOGY. 

Animals  and  plants  have,  as  a  general  phenomenon,  electricity, 
the  potential  energy  of  living  matter.  In  the  animal  the  nerves, 
muscles,  and  glands  are  the  special  seats  of  the  electrical  properties. 
A  muscle  has  three  forms  of  energy — work,  heat,  and  electro-motor 


516 


PHYSIOLOGY. 


activity.  To  study  animal  electricity,  it  is  necessary  to  use  the 
instruments  employed  in  the  physical  laboratory,  but  they  have  to  be 
made  very  sensitive,  since  the  electric  potential  is  feeble  in  animals. 
There  are  usually  employed  three  methods  of  revealing  animal  elec- 
tricity: (1)  the  physiological  rheoscope;  (2)  the  galvanometer;  (3) 
the  capillary  electrometer. 

Physiological  Rheoscope. — This  name   has  been  given   to   the 
nerve-muscle  preparation  of  the  frog  where  the  greatest  possible 

length  of  the  sciatic  nerve  attached 
may  be  used.  The  preparation  of 
the  nerve  requires  special  care,  for 
the  nerve  must  be  removed  by  a 
little  seeker  of  glass  or  bone.  No 
metal  must  touch  it.  It  is  removed 
from  below  upward,  and  if  properly 
done  there  should  be  no  contraction 
of  the  muscle  during  the  operation. 
If  the  nerve  of  this  preparation  be 
brought  into  contact  with  a  segment 
of  separated  muscle  so  as  to  touch 
simultaneously  the  longitudinal  and 
transverse  surfaces,  a  contraction 
instantly  follows. 

G-alvanometer. — The  instru- 
ment usually  employed  is  Thomp- 
son's astatic,  high-resistance,  re- 
flecting galvanometer.  In  this  in- 
strument a  pair  of  suspended  mag- 
nets nearly  astatic  are  surrounded 
by  many  windings  of  fine,  insulated 
wire  with  a  resistance  equal  to  10,- 
000  to  20,000  ohms,  which  explains 
the  name  of  high-resistance  galvano- 
meter. Because  it  has  on  the  upper  magnet  a  slightly  concave 
mirror  by  which  a  ray  of  light  can  be  reflected  on  a  scale,  it  is  also 
called  reflecting.  By  placing  the  point  of  the  unpolarizable  elec- 
trode on  the  center  of  the  longitudinal  surface  of  the  muscle,  and 
the  other  electrode  over  the  center  of  the  freshly  divided  transverse 
surface  of  the  muscle,  and  connecting  the  electrodes  with  the  gal- 
vanometer, with  a  shunt  interposed  between  the  electrodes  and  the 
galvanometer,  it  will  be  seen  that  the  needle  of  the  galvanometer 


Fig.  223. — Thompson  Galvanometer. 


ELECTRO-PHYSIOLOGY. 


517 


deviates.  By  noting  the  deflection  of  the  needle,  it  is  found  that  the 
longitudinal  surface  of  the  muscle  is  positive  and  the  transverse 
section  is  negative.  The  deflection  of  the  needle  is  caused  by  the 
current  of  injury  by  the  transverse  section  of  the  muscle.  It  is 
called  the  demarcation  current,  because  the  difference  of  potential 
appears  at  the  demarcation  between  the  dying  and  the  injured  mus- 
cle. The  injured  part  of  the  muscle  is  negative  to  the  uninjured 
part  and  the  current  in  the  galvanometer  is  from  the  longitudinal 
(positive)  surface  to  the  uninjured  negative  transverse  surface. 

Capillary  Electrometer. — This  instrument  is  an  electrical  mano- 
meter and  shows  electrical  pressure.     It  consists  mainly  of  a  glass 


acid 


Fig.  224. — Diagram  of  Capillary  Electrometer.      (Starling.) 

Hg.,    Mercury.      The    two   terminals    are   represented   as    leading   off   two    points 
at  the  base  and  apex  of  a  frog's  heart,  a  b. 

tube  ending  in  a  fine  point,  which  is  partly  filled  with  clean  mercury 
and  then  placed  in  communication  with  a  pressure  apparatus.  The 
capillary  end  of  the  glass  tube  dips  into  a  tube  containing  mercury 
and  a  20-per-cent.  solution  of  sulphuric  acid.  Into  the  tube  with 
sulphuric  acid  is  fused  a  platinum  wire  which  forms  one  connection 
with  the  lower  column  of  mercury.  Another  platinum  wire  is  con- 
nected with  the  capillary  tube.  Anything  which  alters  the  surface 
tension  will  cause  the  mercury  to  move.  If  now  two  unpolarizable 
electrodes  are  connected  with  a  capillary  electrometer  with  a  short- 
circuiting  key,  and  the  center  of  a  muscle  is  laid  on  one  of  the  non- 
polarizable  electrodes  and  the  divided  transverse  end  on  another  non- 
polarizable  electrode,  then  when  the  mercury  meniscus  is  watched 


518 


PHYSIOLOGY, 


with  a  low-powor  microscope  the  mercury  will  move  in  a  direction 
showing  a  higher  potential  at  the  positive  electrode  on  the  longi- 
tudinal surface. 

Instead  of  a  transverse  section  of  a  muscle  its  tendon  may  be 
taken,  which  is  also  negative  and  has  been  called  the  natural  trans- 


Fig.  225.— Direction  of  Current  of  Daniell  Cell. 

Through  the  galvanometer  the  current  is  from  copper  to  zinc.     Through  the  ceU 
the  current  is  from  zinc  to  copper. 

verse  surface.  The  cut  surface  of  a  longitudinal  section  of  muscle 
presents  positive  electrization.  Tbe  laws  of  electrical  currents  of 
muscle  have  been  fully  determined  by  DuBois-Eeymond : — 

1.  When  the  conductor  unites  the  longitudinal  to  the  transverse 
surface  there  is  a  well-marked  deviation  of  the  needle,  and  the  great- 


Fig.  226.— Direction  of  Current  of  Injured  Muscle.      (Waller.) 
Through  the   galvanometer  the   current   is   from   normal  to  injured   part,   or 

from  resting  to  active  part.     Through  the  muscle  the  current  is  from  injured  to 

normal  part  or  from  active  to  resting  part. 

est  deviation  occurs  when  the  middle  of  the  longitudinal  surface  is 
connected  with  the  middle  of  the  transverse. 

2.  When  tv^o  points  are  connected  on  a  longitudinal  or  trans- 
verse surface  which  are  unequally  distant  from  the  middle,  or  two 
points  unequally  distant  on  opposed  surfaces,  then  there  is  a  slight 
deflection  of  the  needle.     In  the  case  of  the  longitudinal  surfaces  the 


ELECTRO-PHYSIOLOGY. 


519 


current  passes  along  the  conductor  from  the  point  nearer  the  center 
to  the  one  farther  off.     The  reverse  is  the  case  for  the  transverse. 

3.  When  two  points  are  connected  on  the  same  or  on  opposed 
surfaces  equally  distant  from  the  center,  or  when  the  centers  of  two 
opposite  surfaces  are  joined,  there  is  no  movement  of  the  needle  of 
the  galvanometer. 

The  parelectronomic  part  of  the  muscle  is  the  tendinous  part  of 
the  muscle,  which  is  negative  instead  of  being  positive,  as  is  the  rule. 
Here  it  is  necessary  to  make  an  artificial  section  for  the  purpose  of 
demonstrating  the  electrical  phenomena  of  muscle. 


Fig.  227. — Schema  Representing  the  Inequalities  of  Electric  Ten- 
sions upon  the  Natural  Longitudinal  Surface  and  upon  the  Artificial 
Transverse  Surface  of  a  Muscle-cylinder.  Also  the  direction  of  the 
electric  currents  from  the  exterior  to  the  interior  of  the  muscle.  (La- 
HOUSSE.) 


Hermann  has  shown  that  the  muscle-currents  (demarcation  cur- 
rents) are  the  result  of  the  preparation,  and  do  not  exist  in  the  nor- 
mal, intact  fibers  when  in  a  state  of  repose.  These  galvanometrical 
deviations  are  due  to  the  traumatic  action  of  air,  cold,  or  chemicals. 

Electrical  Phenomena  of  Contracting  Muscle. — If  upon  the  elec- 
trodes connecting  the  poles  of  the  galvanometer  a  muscle  is  so  placed 
that  the  needle  deflects,  then  on  tetanizing  the  muscle  by  stimulat- 
ing its  nerve,  the  needle  will  be  seen  to  retrace  its  movement  of 
deflection.  This  reverse  of  the  natural  current  is  known  as  negative 
deviation.  This  has  been  shown  to  be  due  to  a  weakening  of  the 
natural  muscle-current,  and  not  to  the  production  of  a  new  one  con- 


520 


PHYSIOLOGY. 


trary  to  the  current  of  rest.  This  negative  variation  can  stimulate 
the  nerve  of  another  muscle  if  the  nerve  of  the  physiological  rheo- 
scope  be  placed  on  the  contracting  muscle  in  such  a  man- 
ner that  the  first  touches  both  the  cut  surface  and  another  point  on 
the  muscle;  then  each  contraction  of  the  muscle  is  followed  by 
a  contraction  of  frog's  nerve-muscle  preparation  (secondary  con- 
traction).    This  negative  variation  lasts  about  0.00-i  second  and  is 


Time 


Fig.  228. — The  Negative  Variation  (Frog's  Gastrocnemius.) 
(Waller.) 

Simultaneous  record  of  a  tetanic  contraction  (white  line)  and  of  the  accom- 
panying negative  variation  of  a  current  of  injury  (black  line),  (a)  The  Current 
of  injury  is  normally  subsiding;  (b)  it  is  suddenly  diminished  during  tetanus 
(negative  variation);  (c)  it  subsequently  increases  (positive  after-variation);  and 
(d)  it  finally  resumes  its  normal  decline. 

propagated  along  the  muscle  with  the  same  velocity  as  the  wave  of 
contraction  it  precedes,  vanishing  even  before  the  arrival  of  the  lat- 
ter. Hermann  calls  the  negative  variation  by  the  name  of  current 
activity  or  action  current. 


ELECTRO-PHYSIOLOGY.  521 

Diphasic  Variation. — The  base  and  apex  of  the  heart  are  con- 
nected by  unpokirizable  electrodes  to  the  capillary  electrometer. 
When  the  heart  contracts,  there  will  be  a  diphasic  variation.  The 
contracted  portion  at  first  becomes  negative,  and  then  positive,  to 
the  part  not  contracted.  The  first  phase,  base  is  negative  to  the  apex ; 
second  phase,  apex  negative  to  the  base.  The  diphasic  variation  fol- 
lows from  the  fact  that  action  does  not  take  place  at  the  same  time 
throughout  the  whole  heart,  but  takes  time  in  its  transmission  from 
a  point  of  stimulation. 

Nerves. 

The  nerve  presents  differences  in  electric  potential  similar  to 
that  of  the  muscle,  except  it  is  much  weaker.    Every  part  of  its  cut 


Fig.  229. — Arrangement  of  Parts  to  Show  Secondary  Contraction 
in  Muscle.  (After  Rosenthal.)  (From  Mills's  "Animal  Physiology," 
copyright,  1889,  by  D.  Appleton  and  Company.) 

transverse    surface    is   negative,    whilst   its   longitudinal    surface   is 
electro-positive.    You  have  muscle-currents;  also  nerve-currents. 

Negative  Variation  of  the  Nerve-current  or  Action-current. — 
If  you  place  upon  the  electrodes  connected  with  the  galvanometer 
a  piece  of  nerve,  the  deviation  of  the  needle  shows  the  existence  of 
the  nerve-current  already  described  so  long  as  the  nerve  is  at  rest. 
If  you  tetanize  the  nerve  the  needle  is  seen  to  run  back  toward 
zero,  and  sometimes  even  beyond  it.  This  takes  place  in  every  kind 
of  nerve  and  in  the  whole  length  of  the  nerve.  It  can  be  produced 
by  mechanical  or  chemical  stimuli  as  readily  as  with  electricity. 
The  greater  the  stimulus,  the  greater  the  negative  variation,  but 
there  is  not  a  definite  proportion  between  them.  Hermann  has  shown 
that  neither  in  the  nerve  nor  in  the  muscle  do  any  of  these  currents 
exist  so  long  as  the  structures  are  uninjured.  To  generate  a  nerve- 
current  in  repose  it  is  necessary  to  make  a  transverse  section.    This 


522 


PHYSIOLOGY. 


produces  death  of  the  superficial  layer  of  a  segment  next  the  cut  sur- 
face. The  dead  tissue  behaves  negatively  with  regard  to  the  living, 
and  the  electromotor  forces  accordingly  have  their  seat  at  the  plane 
of  demarcation  between  the  dead  and  living.  As  to  the  action  cur- 
rents, they  are  explained  by  admitting  that  during  stimulation 
the  active  parts  are  negative  with  regard  to  the  parts  at  rest. 

Waller  has  compared  the  action  of  ether  and  chloroform  on  the 
electrical  currents  of  a  nerve.  The  movements  of  the  galvanometer 
mirror  are  photographed.  He  has  shown  that  chloroform  is  more 
toxic  than  ether  by  this  method. 

The  nerve  had  in  each  case  a  maximum  dose;  that  is,  for  a 
period  of  one  minute,  air  saturated  with  the  drug,  that  is  about 


Beiore. 


Alter. 


Fig.  230. — Effect  of  Chloroform  upon  the  Electrical  Responses  of 
Isolated  Nerve.      (Waller.) 

The    electrical    response    is    definitely    abolished;     there    is    no    recovery    during 
the  period  of  observation.     With  ether  it  gradually  recovered. 

50  per  cent,  of  ether  and  about  12  per  cent,  of  chloroform.  In  the 
case  of  ether,  the  effect  was  quite  typical,  an  abolition  of  excitability 
in  about  three  minutes.  In  the  case  of  chloroform,  the  excitabi'.ity 
was  promptly  abolished,  and  on  testing  the  nerve  a  half  hour  after- 
wards the  nerve  has  definitely  lost  its  excitability;  that  is,  dead  by 
chloroform. 

Theories  of  Muscle  and  Nerve  Electrical  Currents. — There  are 
two  theories,  one  of  Du  Bois-IJeymond,  the  molecular,  the  other  that  of 
Hermann,  that  of  alteration. 

Molecular  Theory. — The  molecules  may  be  considered  to  be 
positive  on  their  longitudinal  surface,  and  negative  on  their  trans- 
verse section.  Their  negative  surface  is  turned  towards  the  ends 
of  the  muscle  or  nerve,  and  the  positive  surfaces  directed  towards 


ELECTRO-PHYSIOLOGY.  523 

the  longitudinal  surface.  They  are  surrounded  by  a  non-electrie 
conducting  surface.  When  an  electrode  is  placed  on  the  longitu- 
dinal surface  and  would  touch  the  positive  side  of  the  molecules,  the 
other  electrode  on  the  transverse  section  would  be  in  contact  with 
the  negative  side. 

Alteration  Hypothesis. — It  was  shown  that  muscle  not 
injured  exhibited  no  electrical  current.  Hermann  states  that  these 
currents  are  due  to  the  chemical  constitution  of  the  tissue  at  the 
cross-section.  He  believes  that  the  current  is  the  result  of  injury, 
causing  death  of  a  small  part  of  the  muscle  fiber  at  the  cross-section, 
and  so  producing  dilferences  in  potential.  The  difference  of  poten- 
tial arises  at  the  demarcation  between  dying  and  injured  muscle ; 
hence  the  name  "demarcation  current.^'  The  dying  portion  of  the 
cross-section  of  the  muscle  behaves  negatively  to  the  living,  and 
the  electromotive  force  has  its  seat  in  the  demarcation  zone  between 
the  living  and  dying. 

Hering  is  in  accord  with  DuBois-Reymond,  that  the  normal 
resting  muscle  is  the  seat  of  electromotor  forces  which  are  not 
exhibited.  The  electrical  currents  are  due  to  chemical  changes  in 
the  tissues.  Anabolism  causes  a  positive  electrical  phenomenon. 
and  katabolism  a  negative  condition  of  the  part.  The  majority 
of  physiologists  have  accepted  the  alteration  theory  as  the  one  explain- 
ing the  majority  of  the  facts  observed. 

Neither  theory  explains  all  the  facts. 


CHAPTER  XIV. 

THE  ANATOMY  AND  PHYSIOLOGY  OF  THE  NERV0U5 

SYSTEM. 

ANATOMY  OF  THE  NERVOUS  SYSTEM   (EXCEPT  THE 
CEREBELLUM).! 

STRUCTURE  OF  NERYE=TISSUE. 

Nerve-tissues  present  themselves  in  two  varieties:  some  as 
white  substance  and  some  as  gray  substance.  These  two  substances 
are  different,  not  only  in  color,  but  also  in  physical  and  chemical 
properties  and  in  anatomical  arrangement. 

The  gray  substance  contains  as  characteristic  elements  the  nerve- 
cells;  the  white  substance,  the  nerve-fibers.  These  latter  emerge  from 
the  gray  nervous  substance  to  branch  out  toward  the  peripheral 
organs.  These  two  substances,  gray  and  white,  possess  a  common  ele- 
ment known  as  neuroglia;   in  addition,  each  contains  blood-vessels. 

The  Nerve-cell,  or  Neuron. — The  nerve-cell  is  the  characteristic 
fundamental  element  of  the  gray  substance :  it  is  an  independent 
unit  of  the  nervous  system.  It  is  the  element  which  gives  to  this 
kind  of  nervous  tissue  its  gray  color.  When  these  units  are  charged 
with  a  strong  portion  of  pigment,  they  are  black,  as  in  the  locus  niger 
of  the  cerebral  peduncles.  When  a  little  less  pigmented  they  pre- 
sent a  grayish  color:  the  color  that  is  characteristic  of  the  brain 
and  the  central  portion  of  the  spinal  cord.  They  may  be  charged 
with  red  pigment,  then  the  cells  are  reddish;  such  cells  constitute 
the  red  nucleus  of  the  head  of  the  cerebral  crura. 

Structure  of  the  Nerve-cell. — The  nerve-cell  is  composed 
of  (1)  a  mass  of  protoplasm  inclosing  a  nucleus  with  its  nucleolus; 
(2)  of  simple  or  branched  prolongations.  The  protoplasm  of  a 
nerve-cell,  like  that  of  many  other  cells,  is  formed  of  a  very  delicate 
network  of  bands  whose  meshes  are  filled  with  a  clear  or  finely  granu- 
lar albuminoid  substance.  The  network  has  been  designated  by  the 
name  of  spongioplasm  and  the  intermediate  substance  is  generally 
termed  hyaloplasm.  As  to  these  two  components  the  protoplasm  of 
nerve-cells  is  like  that  of  most  other  cells. 

Fibrils. — One  peculiarity  is  the  presence  in  it  of  fibrils  which 
run  through  its  substance. 
(524) 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM. 
3 


525 


Fig.  231. — The  Structure  of  iServous  Tissue.      (Laxdois.) 

1,  Primitive  fibril.  2,  Axis-cylinder.  3,  Remak's  fiber.  4,  Medullated 
varicose  fiber.  5,  6,  Medullated  fiber  with  Schwann's  sheath.  C,  Neurilemma. 
t,  t,  Ranvier's  nodes,  b.  White  substance  of  Schwann,  d,  Cells  of  the  endo- 
neurium.  a.  Axis-cylinder,  x.  Myelin  drops.  7,  Transverse  section  of  nerve- 
fiber.  8,  Nerve-fiber  acted  on  with  silver  nitrate.  /,  Multipolar  nerve-cell  from 
spinal  coid.  s,  Axial  cylinder  process.  //,  Protoplasmic  processes;  to  the  right 
of  it  a  bipolar  cell.  //,  Peripheral  ganglionic  cell  with  a  connective-tissue  cap- 
sule.   ///,  Ganglionic  cell,  with  o,  a  spiral,  and  n,  straight  process.     »»,  Sheath. 

Granules. — The  other  characteristic  feature  of  uerve-proto- 
plasm  is  the  existence  within  it  of  angular  granules.  These  show  a 
special  liking  for  basic  aniline  dyes,  as  methylene  blue.     By  many 


526 


PHYSIOLOGY. 


A 


Fig.  232. 

A  and  B,  Cells  from  the  anterior  horn  of  a  human  spinal  cord.  Fixed  with 
alcohol  and  stained  with  methyl-blue.  C,  Ganglion-cell  fixed  with  alcohol  and 
stained  with  hEematoxylin.  D,  Ganglion-cell  from  anterior  horn  of  foetal  dog. 
(After  an  original  preparation  by  Ramon  y  Cajal.)  Prepared  with  Golgi 
method.     E,  Neuroglia.     (After  an  original  preparation  by  Weigert.) 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.  527 


authors  they  are  spoken  of  as  Nissl  bodies,  after  their  discoverer  and 
the  man  who  has  demonstrated  their  physiological  worth.  The  gran- 
ules are  found  scattered  throughout  the  cell-l)ody  and  its  dendrons,  but 
not  in  the  axis-cylinder  and  the  adjacent  area  of  the  cell  to  which  it  is 
attached. 

The  most  important  relation  that 
these  granules  bear  physiologically  to  the 
cell  is  as  follows:  Under  either  normal 
or  abnormal  activity  of  the  nerve-cell  the 
granules  undergo  a  change  which  has 
been  termed  chroinatolysis.  It  is  slow 
dissolution  of  the  granules  with  diffu- 
sion of  the  degenerated  product  into  the 
protoplasm.  At  first  the  cell  swells, 
pushing  its  nucleus  to  one  side;  later  the 
cell  diminishes  in  size,  due  to  a  loss  of  its 
chromatophilic   substance. 

It  is  in  the  hyaloplasm  that  the  pig- 
ment substance  which  gives  to  the  cell  its 
particular  color  is  deposited. 

In  the  discharge  of  nerve-energy  of 
a  nerve-cell,  Nissl  granules  are  used  up, 
hence  called  by  Marinesco,  kinetoplasm, 
a  source  of  energy.  Nissl  granules  dis- 
appear or  undergo  chromatolysis  after 
high  fever,  after  epileptic  convulsion,  or 
after  poisoning  by  strychnia  or  the  toxins 
of  tetanus  germs.  During  urasmia  the 
cells  of  the  cerebal  cortex  and  of  the  an- 
terior horns  of  the  spinal  cord  show  chro- 
matolysis. Anaemia  produces  similiar 
effects.  Fatigue  in  nerve-cells  can  be 
demonstrated   by   chromatolysis. 

Nucleus. — The  nucleus  of  the  nerve- 
cell  forms  a  small,  rounded  or  oval  mass. 

It  is  characterized  by  its  relatively  large  size.  This  nucleus  is  strongly 
colored  by  all  the  reagents,  such  as  carmine,  methylene  blue,  etc. 
Around  the  nucleus  the  chromatin  forms  a  sort  of  cell-wall  called 
the  nuclear  membrane.  Within  the  nucleus  is  seen  a  small  refract- 
ing body  called  the  nucleolus.  Its  chromatin  is  relatively  great  in 
amount. 


Fig.  233.— Ganglion  Cell 
from  Sympathetic  Ganglion 
of  Frog;  Greatly  Magnified, 
and  Showing  Both  Straight 
and  Coiled  Fibers.  (After 
QuAiN.)  (From  Mills's 

"Animal  Physiology^"  copy- 
right, 1889,  by  D.  Appleton 
and  Company.) 


528  PHYSIOLOGY. 

Cell-prolongations. — From  the  researches  of  Deiters  it  has  been 
learned  that  nearly  every  nerve-cell  has  protruding  from  its  periphery 
a  greater  or  less  number  of  prolongations.  These  are  of  two  vari- 
eties: one  is  unique,  nonbranching,  and  prolonged  under  the  form 
of  a  cylinder-axis  of  a  nerve.  It  is  known  by  the  various  terms,  axis- 
cylinder,  neuraxon,  Deiters'  process,  and  neurite.  The  other  variety  of 
prolongations  is  composed  of  many,  though  an  uncertain,  number  of 
processes.  This  new  set  of  prolongations  bears  the  name  of  proto- 
plasmic processes,  dendrons,  dendrites,  or  the  poles  of  the  cells.  Some 
cells  possess  no  dendrons,  others  .very  many.  However,  it  is  believed 
that  no  cell  is  without  its  neuraxon.  According  to  Cajal,  the  com- 
munication of  the  prolongations  of  the  cells  among  themselves  is 
no  more  than  that  of  simple  contact.  It  is  analogous  to  the  contact 
which  permits  of  the  passage  of  the  electrical  current  when  the  two 
electrodes  of  an  electrical  battery  are  in  contact.  Further,  the  nervous 
impulses  are  transmitted  only  along  the  neuraxons  from  cell  to  cell. 
This  neuraxon,  by  branching  and  coming  in  contact  with  the  dendrons 
of  other  and  neighboring  cells,  conveys  its  impulse  to  them.  They  in 
turn  transmit  it  centripetally  to  the  axis-cylinders  of  their  own  cells  to 
be  further  transmitted  to  other  cells.  The  nerve-cell,  according  to 
this  doctrine,  would  be  physiologically  unipolar.  To  denote  this  close 
contact  existing  between  the  axis-cylinder  and  dendrons  of  various 
cells,  Foster  has  used  the  term  "synapsis." 

Betlie's  Theory  of  Nerve-cell  Connections. — According  to  Bethe, 
when  a  nerve  is  cut  the  nuclei  of  the  neurilemma  can  regenerate  a 
new  "band-fiber"  without  union  with  the  central  stump.  Hence  we 
believe  that  the  axis-cylinder  is  only  an  outgrowth  from  the  nerve-cell. 
According  to  Bethe,  the  neuro-fibrils  go  through  the  nerve-cells  and 
by  a  network  are  placed  in  direct  communication  with  the  neuro- 
fibrils of  other  neurons.  Here  the  cell  has  no  direct  activity  in  the 
conduction  of  impulses  from  one  part  of  the  nervous  system  to  the 
other.  The  neuro-fibrils  alone,  and  the  cellular  network  within  and 
around  the  nerve-cells  with  which  they  connect,  form  the  conduct- 
ing track  that  at  all  points  is  in  continuity. 

The  nerve-cells  of  the  gray  matter  are  of  various  sizes  and 
shapes,  the  branched,  stellate,  or  multipolar  form  being  predominant. 
Some  are  more  or  less  bipolar  or  spindle-shaped;  however,  at  each 
extremity  there  is  usually  a  fine  plexus  of  branches.  Some  are  ovoid 
or  pyriform,  as  in  the  cortex  of  the  cerebellum,  where  they  have 
received  the  name  of  cells  of  Purkinje.  The  cells  of  the  ganglia 
of  the  spinal  nerves  are,  in  great  part,  unipolar. 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM. 


529 


The  dimensions  of  the  nerve-cells  are  very  variable ;  the  smallest 
are  about  V4000  iiich  in  diameter,  the  cells  of  the  posterior  horns  of 
the  spinal  cord  are  from  V2500  to  V1200  inch,  and  the  giant  cells  of 
the  anterior  horns  of  the  spinal  cord  are  about  V250  inch  in  diameter. 

By  employing  Golgi's  silver-nitrate  method  of  staining,  the 
nerve-cells,  with  their  processes,  are  stained  black  from  a  deposition 
of  the  silver.     By  means  of  this,  the  nerve-prolongations  may  be 


.sch 


23-4  235 

Fig.  234. — A  Piece  of  Medullated  Nerve-fibril  of  Man,  Nucleus  and  Axis 
Cylinder  Stained  by  Carmine.      (Sobotta.  ) 

a,  Axis  cylinder.    A-,  Nucleus,    m.  Medulla,    n.  Neurilemma  (Schwann's  sheath). 

Fig.  235. — A  Piece  of  Medullated  Nerve  of  Man.     It  shows  Ranvier's 
Constrictions  and   Lantermann's  Incisures.      (Sobotta.) 

m.   Medulla,     sch,   Ranvier's  constrictions. 


traced  to  their  ultimate  terminations.  This  method  beautifully  dem- 
onstrates the  distribution  of  the  neurites,  their  branching,  and  man- 
ner of  contact  with  dendrites  of  contiguous  cells;  also,  how,  as  a 
rule,  the  neuraxon  does  no  very  immediate  branching.  It  must  be 
stated,  though,  that  usually  from  the  neuraxon  there  proceed  numer- 
ous fine  fibrils  to  which  the  term  collaterals  is  applied.  These  are  in 
communication  with  the  dendrites  of  the  neighboring  cells.  In  nerve- 
centers,  the  neuraxon,  after  proceeding  for  some  distance,  does  really 


530  PHYSIOLOGY. 

branch  to  form  arborizations  to  come  into  contact  witli  nerve-den- 
drites. 

The  JSTerve-fibers. — Every  nerve-fiber  is  a  process  of  a  nerve- 
cell.  It  is  the  neuraxon  of  some  particular  cell.  It  is  the  medium 
which  conducts  impulses  to  or  from  the  tissues  and  organs,  on  the 
one  hand,  and  the  nerve-centers,  on  the  other.  In  the  majority  of 
cells  the  neuraxon  acquires  a  sheath  to  be  thus  converted  into  a 
medullated  nerve-fiber.  Thus,  there  are  two  kinds  of  nerve-fibers: 
medullated,  or  those  with  myelin;  and  nonmeduUaied,  or  those  without 
myelin. 

Medullated  Fibers  in  the  fresh  condition  are  bright,  glistening 
cylinders  showing  a  dark,  double  contour.  The  essential  part  of  the 
fiber  is  the  axis-cylinder.  This  is  a  soft,  transparent  rod,  or  thread, 
which  runs  from  one  end  of  the  fiber  to  the  other.  It  does  not 
anastomose  with  its  neighbors,  and  in  the  average  nerve  is  about  V1200 
inch  in  diameter.  After  the  employment  of  certain  reagents  the 
axis-cylinder  shows  itself  to  be  composed  of  very  fine,  homogeneous 
or  more  or  less  beaded  fibrillfe.  The  latter  are  the  elemejitary,  or 
primitive  fibrillw.  They  are  held  together  by  a  small  amount  of  a 
faintly  granular,  interstitial  substance.  The  thickness  of  the  axis- 
cylinder  is  in  direct  proportion  to  the  thickness  of  the  whole  nerve- 
fiber.  The  axis-cylinder  is  enveloped  in  its  own,  more  or  less  elastic, 
hyaline  sheath. 

The  axis-cylinder  is  not  regularly  cylindrical,  but  is  slightly  nar- 
rowed in  places.  Under  the  influence  of  silver  nitrate  applied  to  its 
surface  there  appear  alternate  obscure  and  clear  transverse  striae. 
They  are  the  so-called  lines  of  Frommann. 

Myelin. — Surrounding  the  axis-cylinder  is  the  myelin,  medullary 
sheath,  or  the  white  substance  of  Schwann.  It  is  a  layer  of  fatty  sub- 
stance, strongly  refracting,  and  of  homogeneous  aspect.  It  is  colored 
black  by  osmic  acid.  It  is  the  myelin  which  gives  to  the  nerve  its 
double  contour.  It  is  composed  of  a  network  of  fibrils  of  a  chemical 
substance  called  neurol-eratin,  which  incloses  the  semi-fluid,  fatty  sub- 
stance. The  latter  contains,  among  other  substances,  a  complex, 
phosphorized  fat. 

The  sheath  of  myelin  envelops  the  axis-cylinder  everywhere,  ex- 
cept at  its  termination  and  at  the  nodes  of  Eanvier. 

In  its  arrangement  the  myelin  is  imbricated  in  the  fashion  of 
tiles  on  a  roof  by  reason  of  a  series  of  segments  one  above  the  other. 
They  are  separated  one  from  the  other  by  clear  lines.    The  lines  are 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.  531 

known  as  the  incisures  of  Lantermann,  and  the  segments  as  those  of 
Schmidt. 

Neurilemma. — The  neurilemma  or  sheath  of  Schwann,  sur- 
rounds the  medullary  sheath  to  form  the  outer  boundary  of  the  nerve- 
fiber.  It  is  a  thin,  elastic,  very  delicate,  hyaline,  and  transparent  mem- 
brane. It  is  comparable  to  the  cell-wall  of  a  cell.  Between  the  neu- 
rilemma and  medullary  sheath  there  are  irregularly  scattered  ovoid 
nuclei.  They  are  the  nerve-corpuscles,  and  are  analogous  to  the 
muscle-corpuscles  previously  mentioned.  Each  nerve-corpuscle  is  sur- 
rounded by  a  thin  zone  of  protoplasm. 

Between  the  myelin  layer  and  the  neurilemma  is  a  thin  zone  of 
protoplasm.  When  this  arrives  at  the  level  of  the  annular  constric- 
tions it  is  reflected  upon  itself  to  line  the  internal  surface  of  the 
myelin  layer  (Mauthner's  membrane).  The  protoplasm  is  also  insinu- 
ated into  the  incisures  of  Lantermann  and  decomposes  the  layer  of 
myelin  into  the  superposed  segments  of  Schmidt. 

Nodes  of  Ranvier. — At  intervals  of  about  one  micromillimeter 
along  the  course  of  the  nerve  there  appear  constrictions :  the  nodes 
of  Eanvier.  At  these  points  the  myelin  sheath  is  interrupted  so  that 
the  neurilemma  appears  to  do  the  constricting.  That  portion  of  the 
nerve-fiber  between  any  two  constrictions  is  termed  an  internodal  seg- 
ment. At  about  the  center  of  each  internodal  segment  is  located  one, 
sometimes   more,   nerve-corpuscles. 

Such  is  the  composition  of  a  medullated  nerve-fiber.  This  type 
of  nerve  is  found  chiefly  in  the  white  matter  of  the  nerve-centers  and 
in  the  cerebro-spinal  nerves,  with  the  exception  of  the  olfactory  nerve. 

NoNMEDULLATED  Nerve-fibers. — They  occur  especially  in  the 
S3Tnpathetic  system,  but  are  also  present  to  a  slight  extent  in  the 
cerebro-spinal  nerves. 

Each  fiber  consists  of  a  bundle  of  fibrils — primitive  fibrils — 
which  are  inclosed  in  a  delicate,  transparent,  and  elastic  sheath.  The 
fibrils  are  very  delicate  and  somewhat  flattened.  Here  and  there  along 
the  course  of  the  fibrils  will  be  found  oval  nuclei.  These  latter  lie 
between  the  axis-cylinders  and  their  enveloping  neurilemma.  As 
these  fibrils  contain  no  myelin,  they  are  not  blackened  by  osmic  acid. 
This  allows  of  a  differentiation  between  medullated  and  nonmedul- 
lated  nerves  when  examining  the  nerve-supply  of  a  tissue. 

Nerve-trunkS  consist  of  bundles  of  nerve-fibers.  Each  bundle, 
of  course,  contains  a  greater  or  less  number  of  fibrils.  Several  bun- 
dles are  held  together  by  a  common  connective-tissue  sheath :  the 
epineurium.    Delicate  fibrils  lie  between  the  nerve-fibers  to  constitute 


532  PHYSIOLOGY. 

the  endoneurium.  The  larger  blood-  and  lymph-  vesssls  lie  in  the 
epincuriiim;  the  few  capillaries  of  the  nerve-fibers  lie  supported  in 
the  endoneurium. 

Eegeneration  of  United  Nerves. — If  a  nerve  is  cut,  its  peri- 
pheral end  undergoes  degeneration.  The  fiber  breaks  up  into  small 
pieces  of  myelin,  each  holding  a  piece  of  neuraxon  which  is  finally 
absorbed.  Eepair  of  the  nerve  begins  wholly  during  the  degenera- 
tion. The  nuclei  of  the  neurilemma  increase  in  number  to  form 
around  them  a  layer  of  protoplasm  or  cytoplasm.  At  length  the 
cytoplasm  becomes  a  continuous  piece  of  protoplasm,  and  the  fiber 
thus  produced  is  known  as  a  "band-fiber."  Then  there  is  an  arrest  of 
regeneration  unless  the  peripheral  fiber  is  anatomically  united  to  its 
central  connection.  If  the  central  and  peripheral  ends  are  brought 
together,  then  the  "band-fiber"  becomes  changed  into  a  normal  nerve- 
fiber,  with  a  sheet  of  myelin  and  a  cylinder  axis.  The  axis  cylinder 
in  the  peripheral  end  of  the  nerve  is  supposed  to  grow  out  from  the 
central  end  of  the  nerve. 

Termination  of  the  Nerve. — After  a  certain  course  in  the  trunk 
of  the  nerve  the  nerve-fiber  divides  at  the  periphery  into  a  terminal 
plaque,  the  motor  plaque  of  muscles;  or  into  a  sense-cell,  as  in  the 
retinal  cells  or  organ  of  Corti;  or  into  a  sense-corpuscle,  as  a  tactile 
corpuscle;  or  into  numerous  fibrils  which  anastomose  to  form  a 
terminal  plexus,  as  in  the  cornea. 

Nonmedullated  Fibers,  that  is,  those  that  are  naked,  pale  or 
gray,  and  reduced  to  an  axis-cylinder  and  sheath,  branch  and  form 
networks — their  peripheral  terminations.  This  mode  of  termination 
occurs  in  the  nerve-fibers  of  common  sensation,  as  in  many  of  the 
nerve-fibers  of  the  skin,  cornea,  and  mucous  membrane.  In  all  of 
these  cases  the  peripheral  termination  fibrils  are  intra-epithelial : 
that  is,  they  are  situated  in  the  epithelial  portions  of  cornea,  mucous 
membrane,  etc. 

Neuroglia. — In  the  gray,  as  well  as  in  the  white,  substance  of 
the  nerve-centers  there  exists  between  the  cells  and  nerve-fibers  an 
intervening  substance  which  has  been  termed  neuroglia.  It  must  not 
be  confounded  with  the  true  connective  tissue  along  the  course  of 
the  blood-vessels  in  the  nerve-centers.  Its  chemical  nature  is  wholly 
different  from  the  latter,  which  is  always  derived  from  the  mesoblast. 
Ranvier  has  shown  that  neuroglia  is  derived  from  the  primitive  neuro- 
blast or  epiblast. 

Neuroglia  sometimes  presents  itself  in  the  shape  of  very  fine  fila- 
ments assembled  in  a  very  close  network,  as  in  the  gray  substance. 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.  533 

Sometimes,  again,  it  is  seen  imder  the  aspect  of  reticulated  plates 
bounding  the  space  in  which  the  nerve-fibers  pass.  This  is  beautifully 
demonstrated  in  the  white  substance  of  the  columns  of  the  spinal  cord. 

Elsewhere  the  neuroglia  is  found  to  be  a  homogeneous,  gelatini- 
form  substance,  as  in  the  ependyma  of  the  spinal  cord  or  in  the  gela- 
tinous substance  of  Eolando  in  the  postero-lateral  groove  of  the  same 
structure. 

Besides  the  fibers  and  plates  already  mentioned,  neuroglia  con- 
tains cells.  These  are  star-shaped,  flat,  and  nucleated.  They  have 
numerous  prolongations.  By  the  aid  of  these  prolongations  the  cells 
of  the  neuroglia  anastomose  freely  with  one  another  to  form  a  very 
complicated  network.    This  incloses  in  its  meshes  the  nerve-elements. 

Neuroglia  enjoys  the  role  of  a  true  cement  which  unites  all  of 
the  fibers  and  nerve-cells. 

Classification  of  Nerve-cells. — According  to  Schafer,  nerve-cells 
are  broadly  classified  into:  "1.  Afferent  cells,  which  receive  impres- 
sions at  the  periphery  to  convert  them  into  impulses.  The  latter  then 
pass  toward  the  central  nervous  system.  2.  Efferent  cells,  which  send 
out  nervous  impressions  toward  the  periphery.  3.  Intermediary  cells, 
which  receive  impressions  from  afferent  cells  to  tfansmit  them  directly 
or  indirectly  to  efferent  cells.  4.  Distributing  cells,  which  occur  near 
the  periphery,  and,  receiving  impulses  from  efferent  cells,  distribute 
them  to  involuntary  muscles  and  secreting  cells.  The  cells  of  this 
class  belong  to  the  so-called  sympathetic  system. 

"The  afferent  and  efferent  cells  are  kno^voi  as  root-cells.  The 
greater  number  of  the  nerve-cells  of  the  brain  and  cord  belong  to  the 
intermediate  class.  They  serve  the  purposes  of  association  and 
coordination  and  afford  a  physical  basis  for  psychical  phenomena." 
Efferent  fibers  are  also  called  cellulifugal.  Afferent  fibers  are  also 
called  cellulipetal. 

Structure  of  the  Gray  Substance. — The  gray  matter  is  formed 
(1)  of  nerve-cells,  (2)  of  neuroglia-cells,  (3)  of  fibril  elements  repre- 
senting the  prolongations  of  nerve-  and  neuroglia-  cells,  (4)  of  an 
intervening  network  formed  by  the  branching  fibrils,  and  (5)  of 
blood-vessels.  Elements  1,  2,  and  3  (here  enumerated)  of  the  struc- 
ture have  been  treated  previously  in  detail. 

The  blood-vessels  penetrate  the  gray  substance,  and  are  sur- 
rounded with  a  layer  of  connective  tissue  coming  from  the  pia  mater, 
which  they  have  received  in  their  passage  along  and  through  this 
membrane.  The  connective  tissue  forms  sheaths  around  the  capillary 
network,  arterioles,  and  little  veins,  in  which  the  vessels  seem  to  float. 


534 


PHYSIOLOCY. 


These  liavo  been  termed  tlie  perivascular  .sheaths  of  His.  Between 
them  and  the  vessels  exists  a  lymph-space :  one  of  the  origins  of  the 
lymphatics. 

White-substance  Formation. — The  white  matter  is  formed  by  the 
bundles  of  white  fibers  covered  by  a  lamellar  investment  of  neuroglia. 
These  bundles  are  separated  from  one  another  by  tracts  of  connective 
tissue  detached  from  the  pia  mater. 

Axis-cylinders  are  also  found,  which  come  from  the  gray  matter. 
Blood-vessels  anastomose  and  run  in  a  course  parallel  with  the  nerve- 
fibers.  This  circulatory  network  likewise  has  a  perivascular  sheath  as 
has  that  in  the  gray  sul)stance. 

Chemical  Properties  of  Nervous  Substance. — The  following  table 
of  Landois  gives  the  percentage  of  the  various  components  of  both 
gray  and  white  matters : — 


Chemical  Composition  of 


Gray  Matter. 


White  Matter. 


Water 

Solids 

The  solids  consist  of  : — 
Proteids  (globulins)  .  .  . 
Lecithin  ..... 
Cholesterin  and  fats  .... 
Cerebrin  ... 
Substances  insoluble  in  ether 
Salts       


81.6  per  cent. 
18.4         " 


55.4  per  cent. 
17.2         " 
18.7         " 

0.5 

6.7         " 

1.5 


68.4  per  cent. 
31.6         " 


24.7  per  cent. 

9.9 
52.1 

9.5 

3.3 

0.5 


In  100  parts  of  ash.  Breed  found  potash,  33 :  soda,  11 ;  magnesia, 
2;  lime,  0.7;  NaCl,  5;  iron  phosphate,  1.2;  fixed  phosphoric  acid, 
39 ;   sulphuric  acid,  0.1 ;   and  silicic  acid,  0.4. 

Composition  of  Nerve-tissue,  According  to  Halliburton. — (a) 
Proteids.     Over  50  per  cent,  in  gray  matter.     They  are : — 

1.  Neuro-globulin  (alpha),  coagulates  at  47°  0. 

2.  A  nucleo-proteid  which,  like  other  proteids.  causes  ex- 

tensive intravascular  coagulation. 

3.  A  neuro-globulin  (beta). 
(&)   Nuclein  from  nuclei  of  cells. 

(c)  N"euro-keratin,  from  neuroglia. 

(d)  Phosphorized  fats. 

1.  Lecithin;    when   decomposed   it   gives   rise   to   glycero- 
phosphoric  acid,  stearic  acid,  and  choline. 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.  535 

2.  Protagon. 

3.  Kephalins, 

(e)    Cerebrins   (nitrogenized  substances),  or 

Cerebrosides.  The  name  cerebrosides  indicates  that  they  are 
glucosides,  and  that  the  sugar  (cerebrose)  obtained  from 
them  has  been  identified  as  galactose. 

(/)  Cholesterin. 

(g)   Extractives:    creatin,   xanthin,   hypoxanthin.   inosite,   lactic 
acid,  uric  acid,  and  urea. 

(h)   Gelatin. 

(t)   Inorganic    salts,    of    which    the    alkaline    phosphates    and 
chlorides  are  the  most  abundant. 

Haitai  has  shown  that  lecithin,  when  administered  to  white  rats, 
caused  a  gain  of  60  per  cent,  in  body  weight  compared  with  the  nor- 
mal animal.    Hence  lecithin  is  a  stimulant  of  normal  growth. 

Eeaction". — When  passive,  nerve-tissue  is  neutral  or  feebly  alka- 
line.   When  active  or  dead  it  is  said  to  be  acid. 

It  is  found  that  after  death  nerves  have  a  more  solid  consistence. 
Probably  some  coagulation  occurs  which  is  to  be  compared  to  the 
stiffening  of  muscle.  Simultaneously  there  is  generated  and  liberated 
a  free  acid. 

Mechanical  Properties. — A  remarkable  property  of  nerve-fibers 
is  the  absence  of  elastic  tension  according  to  the  varying  positions  of 
the  body.    Divided  nerves  do  not  retract. 

The  cohesion  of  a  nerve  is  an  important  property.  Oftentimes 
when  a  limb  is  forcibly  torn  from  the  body  the  nerve  still  remains 
intact  (though  considerably  stretched),  while  the  other  soft  tissues 
are  completely  severed.  The  sciatic  nerve  at  the  level  of  the  popliteal 
space  requires  a  force  equal  to  one  hundred  and  ten  or  one  hundred 
and  twelve  pounds  to  rupture  it ;  the  median  or  ulnar  require  forces 
equal  to  forty  or  fifty  pounds.  The  latter  nerves  will  stretch  six  or 
eight  inches  before  the  point  of  ru])ture  is  reached.  It  is  upon  the 
knowledge  of  this  fact  that  the  method  of  nerve-stretching  is  employed 
in  some  forms  of  neuralgia. 

Nerve-metabolism. — Some  extractives  are  obtained  which  are 
believed  to  bo  decomposition  products  of  the  nerve. 

The  Nerve-centers. — The  nerve-fibers  and  nerve-cells  comprise 
the  essentials  from  which  the  nerve-centers  are  formed  ;  the  elements 
must,  of  course,  be  held  together  by  enveloping  neuroglia.  The  term 
center  is  merely  applied  to  an  aggregation  of  nerve-cells  which  are 
so  related  to  one  another  as  to  subserve  a  certain  function.     These 


536  PHYSIOLOGY. 

cells  give  off  numerous  i^'occssos  whereby  they  are  brought  into 
direct  communication  witli  one  another  as  well  as  other  parts  of  the 
body.  These  masses  thus  form  structural  integrations  which  per- 
form corresponding  integral  functions.  If  at  any  time  the  struc- 
ture suffers,  the  function  must  of  necessity  suffer  also. 

The  nerve-centers  comprise  the  spinal  cord,  medulla  oblongata, 
pons  Varolii,  cerebrum,  and  cerebellum. 

Common  Pkoperties. — There  are  certain  properties  which  all 
nerve-centers  seem  to  possess  in  conunon  and  which  arc  of  interest 
to  the  student: — 

1.  They  all  contain  nerve-cells.  These  are  the  real  centers  of 
activity.  They  both  originate  and  conduct  impulses.  Nerve-fibers 
are  almost  exclusively  conductors. 

2.  Nerve-centers  are  capable  of  discharging  reflexes.  They  are 
motor,  secretory,  and  inhibitory  reflexes. 

3.  They  are  the  seat  of  automatic  excitement  when  phenomena 
are  manifested  without  the  application  of  any  apparent  external 
stimulus. 

4.  The  nerve-centers  are  trophic  centers  for  both  their  nerves 
and  the  tissues  supplied  by  them. 

THE  SPINAL  CORD. 
Structure  of  the  Spinal  Cord. 

"The  key  to  the  study  of  the  central  nervous  system  is  to  re- 
member that  it  begins  as  an  involution  of  the  epiblast.  It  is  orig- 
inally tubular  with  a  central  canal  whose  brain-end  is  dilated  into 
ventricles.  In  the  spinal  cord  there  are  three  concentrated  parts: 
First,  the  columnar,  ciliated  epithelium;  outside  of  this  is  the  cen- 
tral gray  tube ;  and,  covering  all,  the  outer  white,  conducting  fibers." 
(Hill.) 

The  spinal  cord  is  that  portion  of  the  cerebro-spinal  axis  which 
is  inclosed  within  the  vertebral  canal.  It  extends  in  the  form  of  a 
large,  cylindrical  cord  from  the  upper  level  of  the  atlas  to  the  first 
or  second  lumbar  vertebra.  Above  it  is  continuous  with  the  medulla 
oblongata.  Below  it  becomes  conical,  to  terminate  finally  in  a  slen- 
der filament :  the  filam  terminalc.  It  is  attached  to  the  base  of  the 
coccyx.  The  filum  terminate  passes  through  and  is  partly  concealed 
by  the  conical  extremity  of  the  spinal  cord.  The  cone  is  a  mass  of 
nerve-roots  Avhich,  from  its  striking  resemblance  to  a  horse's  tail, 
has  been  termed  the  cauda  equina. 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.  537 

The  average  length  of  the  spinal  cord  is  eighteen  inches.  In  the 
foetus  the  cord  extends  the  whole  length  of  the  vertebral  canal.  The 
difference  in  relative  length  of  the  cord  in  the  foetus  and  in  the 
adult  is  due  to  the  unequal  and  more  rapid  growth  of  the  spinal 
canal  than  of  the  cord.  The  cord  thus  seems  to  ascend  in  its  canal. 
Instead  of  the  spinal  nerves  of  the  lower  portion  of  the  cord  leaving 
their  points  of  emergence  horizontally,  they  sweep  down  like  the 
hairs  in  the  tail  of  a  horse  to  form  the  aforementioned  cauda  equina. 

Coverings. — Not  only  is  the  cord  protected  by  the  spinal  canal 
in  which  it  is  suspended,  but  in  addition  it  is  enveloped  by  a  triple 
membranous  container.  The  cord  does  not  more  than  half  fill  the 
lumen  of  the  spinal  canal.  It  is  suspended  in  this  cavity  surrounded 
by  an  aqueous  medium :    the  cerebrospinal  fuid. 

The  investing  membranes  have  been  termed,  from  within  out- 
ward, pia  mater,  arachnoid,  and  dura  rnater.  They  form  a  sheath,  or 
theca,  which  is  considerably  larger  than  the  cord.  It  is  separated 
from  the  bony  wall  of  the  spinal  canal  by  venous  plexuses  and  loose 
areolar  tissue. 

The  pia  mater  is  a  very  delicate  covering  which  is  closely 
adherent  to  the  cord.  It  sends  numerous  septa  into  the  substance 
of  the  cord  as  well  as  into  its  anterior  and  posterior  median  fissures. 
It  is  composed  of  blood-vessels  and  connective  tissue. 

The  arachnoid  (spider's  web)  is,  as  its  name  implies,  a  very  deli- 
cate, reticular  membrane.  It  is  nonvascular.  Hanging  like  a  cur- 
tain between  the  innermost  and  outermost  membranes,  it  forms  two 
spaces  which  are  termed  subdural  and  suharachnoid. 

The  outermost  and  toughest  membrane  is  the  dura  mater.  It 
is  a  very  dense  sheath  and  lies  indirectly  in  contact  with  the  canal- 
wall.  However,  unlike  the  dura  of  the  brain,  it  does  ?iot  form  the 
periosteum  for  the  portions  of  the  vertebra  constituting  the  walls  of 
the  spinal  canal. 

Diameter  of  the  Cord. — The  volume  of  the  cord  is  not  the  same 
throughout  its  whole  extent.  Although  of  a  mean  diameter  of  half 
an  inch,  yet  it  presents  two  decided  enlargements. 

The  one  enlargement  is  at  the  level  of  the  inferior  portion  of 
the  cervical  region;  the  other  at  the  lower  portion  of  the  dorsal 
region.  The  first  one  is  the  cervical  enlargement  from  which  emerge 
the  nerves  of  the  upper  extremity.  The  name  brachial  enlargement 
has  been  given  to  it. 

From  the  lower  enlargement  arise  the  nerves  which  proceed  to 
the  lower  extremities.     It  is  known  as  the  lumbar  enlargement.     At 


538  PHYSIOLOGY. 

the  site  of  each  enlargement  the  cord  loses  its  cylindrical  form  to 
become  somewhat  flattened  from  before  backward. 

The  formation  of  the  enlargements  is  in  intimate  relation  with 
the  development  of  the  members.  In  fishes  we  have  only  rudiment- 
ary members,  the  cord  is  of  uniform  diameter  throughout.  In  steel- 
workers  the  cervical  swelling  is  considerable. 

The  ivelght  of  the  cord  is  about  one  and  one-fourth  ounces;  it  is 
equal  to  about  one-forlieth  of  the  weight  of  the  brain. 

The  suspension  of  the  spinal  cord  within  the  canal  is  main- 
tained laterally  by  irregular  fibrous  tracts  which  form  the  ligamentum 
denticulatum.  Laterally  the  roots  of  the  spinal  cord  give  support; 
below,  the  filum  terminale  fastens  it  to  the  coccyx;  above,  its  con- 
tinuation as  the  medulla  furnishes  the  most  important  support. 

Exterior  Form  of  the  Cord. — Externally  the  cord  has  two  longi- 
tudinal median  grooves:  one  anterior,  the  other  posterior.  They 
traverse  the  entire  length  of  the  cord  to  divide  it  into  two  halves 
which  are  usually  perfectly  symmetrical.  The  origins  of  the  spinal 
nerves  are  situated  upon  each  side  of  these  two  parallel,  longitudinal 
lines. 

The  anterior  median  groove  divides  the  anterior  surface  of  the 
cord  into  two  perfectly  equal  parts.  It  extends  from  the  decussa- 
tion of  the  pyramids  to  the  caudal  extremity  of  the  cord.  In  depth 
it  occupies  nearly  a  third  of  the  thickness  of  this  organ.  In  this 
groove  is  folded  a  layer  of  pia  mater;  at  its  base  is  seen  a  layer  which 
passes  from  one-half  of  the  cord  to  the  other — the  white,  or  anterior, 
commissure. 

The  posterior  median  fissure,  deeper  and  narrower  than  the 
anterior,  extends  from  the  nib  of  the  calamus  scriptorius  to  the 
termination  of  the  spinal  cord.  Into  this  groove  the  pia  mater  sends 
but  a  simple  partition;  but  it  is  very  adherent  to  the  walls  of  the 
groove.  The  depth  of  the  fissure  is  bounded  by  a  commissure  analog- 
ous to  that  which  is  furnished  to  the  anterior  median  groove,  but  of 
a  gray  color.     This  is  the  gray,  or  posterior,  commissure. 

Upon  each  side  of  the  cord  are  seen  two  lateral  grooves  which 
represent  the  lines  of  implantation  of  the  anterior  and  posterior 
roots.  They  are  known  as  the  antero-  and  postero-lateral  grooves. 
The  latter  is  the  more  apparent  of  the  two,  showing  itself  in  the 
form  of  a  dotted,  longitudinal  line. 

The  antero-lateral  groove  corresponds  to  the  line  of  insertion 
of  the  anterior  roots  of  the  spinal  nerves.     The  two  lateral  grooves 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.  539 

may  be  regarded  as  purely  artificial;  seen  only  after  the  spinal  nerves 
are  torn  from  the  cord. 

By  virtue  of  the  median  and  lateral  fissures  the  cord  is  divided 
into  columns,  paired  and  symmetrical.  The  portion  comprised  be- 
tween the  anterior  median  and  the  antero-lateral  fissures  is  known 
as  the  anterior  column.  That  portion  between  the  two  lateral  fissures 
bears  the  name  of  lateral  column.  That  part  between  the  postero- 
lateral and  posterior  median  groove  is  the  posterior  column. 

Anatomy  and  physiology  demonstrate  that  the  separation  of  the 
anterior  from  the  lateral  column  is  not  complete;  hence  it  is  cus- 
tomary to  reunite  these  two  columns  under  the  name  of  antero- 
lateral columns. 

Internal  Conformation  of  the  Spinal  Cord. — The  texture  of  the 
cord  is  best  studied  by  means  of  transverse  section.  These  sections 
show  that  the  cord  is  composed  throughout  its  whole  extent  of  two 
substances:  one,  the  cortical,  white  substance;  and  the  other,  the 
central,  gray  suistarice. 

The  white  substance  is  located  peripherally  and  covers  all  of  the 
gray  substance  except  at  the  base  of  the  posterior  median  groove.  It 
forms  the  columns  which  have  Just  been  pointed  out. 

The  gray  substance  forms  in  each  half  of  the  cord  a  longitudinal 
column  whose  transverse  section  appears  in  the  form  of  a  crescent 
with  its  concavity  directed  externally.  The  crescent  terminates  in 
two  swollen  extremities,  the  anterior  one  having  the  name  of  anterior 
horn;  the  posterior  one,  that  of  the  posterior  horn. 

The  two  crescents  are  bound  to  one  another  at  their  convexity 
by  the  aid  of  a  transverse  band  of  gray  substance,  the  gray  commis- 
sure. This  band  is  pierced  centrally  by  a  canal,  the  central  canal  of 
the  cord.  It  runs  down  the  central  axis  of  the  cord  and  is  accom- 
panied on  each  side  by  a  vein,  the  central  veins  of  the  cord.  In  all 
sections  the  gray  matter  is  vaguely  represented  by  the  letter  H:  per- 
haps better  by  the  two  wings  of  a  butterfly  united  by  a  transverse 
bar.  The  column  of  gray  matter  is  not  exactly  of  the  same  form 
in  its  whole  length.  It  is  thicker  in  the  cervical  and  lumbar  regions 
than  in  the  thoracic.  The  white  matter  is  likewise  thicker  at  the 
level  of  the  cervico-dorsal  and  lumbar  enlargements.  At  the  level 
of  the  Cauda  equina  the  white  substance  forms  but  an  enveloping 
layer  for  the  gray  matter. 

In  the  cervical  and  lumbar  regions  the  anterior  cornua  are 
remarkable  for  their  volume;  toward  the  dorso-lumbar  enlargements 
the  posterior  cornua  increase  in  size.     The  anterior  cornu  of  the 


540 


PHYSIOLOGY. 


crescent  is  swollen.  The  posterior  is  more  slender  and  reaches  to 
the  surface  of  the  cord.  Each  cornii  possesses  a  swelling  (head)  and 
a  somewhat  restricted  portion  (cervix). 

The  head  of  the  posterior  cornu  is  remarkable  in  that  it  is 
capped  with  a  layer  of  neuroglia  to  which  has  been  given  the  name 
of  gelatinous  substance  of  Rolando.  It  is  nearly  amorphous,  and,  in 
section,  gives  an  appearance  very  similar  to  the  small  letter  u.  The 
substantia  contains  a  few  neuroglia  cells,  with  some  fusiform  nerve- 
cells  along  its  margin. 


Fig.  236. — Two  Nerve-pairs  at  Their  Origin  in  the  Spinal  Cord — 
Anterior  and  Posterior  Roots.      (Morat.) 

As  regards  the  upper  pair  the  figure  shows  the  relation  of  the  roots  with 
the  gray  axis.  In  the  lower  pair  is  seen  the  emergence  of  the  anterior  roots 
at  the  surface  of  cord. 

In  the  inferior  cervical  and  superior  thoracic  region  the  most 
lateral  portion  of  the  anterior  cornu  is  shaped  in  a  special  fashion  so 
as  to  constitute  a  particular  prolongation.  This  is  known  as  the 
lateral  cornu,  or  mtermedio-lateral  column.  The  cells  of  this  column 
are  arranged  in  groups  of  from  eight  to  twelve  bipolar  cells  whose 
long  axes  are  vertical  or  more  or  less  oblique.  It  is  believed  that 
these  give  origin  to  those  fine  medullated  fibers  which  form  the 
splanchnic  efferent  fibers. 

On  examination  of  sections  it  is  seen  that  the  anterior  cornua 
do  not  reach  to  the  surface  of  the  cord.     Hence  that  portion  of  the 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.  541 

white  substance  which  surrounds  the  anterior  cornua  reaches  from 
the  anterior  median  groove  to  tlie  posterior  cornua.  It  seems  to 
form  a  homogeneous  column:   the  antero-Iateral  column. 

In  the  rear,  on  the  contrary,  the  posterior  cornua  sharply  sepa- 
rate the  preceding  to  form  posterior  columns.  They  lie  between  the 
posterior  median  groove  and  the  posterior  cornua.  In  the  cervical 
region  the  posterior  column  is  sharply  divided  into  two  secondary 
columns  by  the  posterior  intermediate  groove.  These  are  the 
columns  of  GoU  (next  to  the  posterior  median  groove)  and  Burdach 
(in  apposition  with  the  posterior  cornu). 

From  measurements  by  Stilling  it  seems  that  the  cervical  swell- 
ing results  from  a  localization  of  superdevelopment  of  both  gray  and 
white  matter  of  the  cord.  The  lumbar  enlargement  is  almost  exchi- 
bively  formed  by  a  localized  superdevelopment  of  gray  substance. 
This  is  readily  explained  by  the  constitution  of  the  columns  them- 
selves. Excepting  the  fibers  forming  the  roots  of  the  spinal  nerves, 
the  columns  of  white  matter  are  formed  of  (lescenclin-g,  or  motor,  and 
ascendhuj,  or  sensory,  fibers.  The  motor  bundle  successively  gives  off 
fibers  to  the  motor  roots  of  the  spinal  nerves  to  such  a  degree  that 
in  their  descent  their  volume  proportionately  diminishes. 

The  sensory,  or  ascending,  bundle,  receiving  fibers  from  each 
posterior  root  which  comes  from  a  sensory  nerve,  enlarges  as  it 
ascends.  Hence  it  results  that  at  the  level  of  the  lumbar  enlarge- 
ment the  bundles  are  at  a  minimum,  the  ascending  bundle  just  com- 
mencing, while  the  descending  bundle  is  nearly  spent. 

Minute  Constitution  of  the  Cord. — The  spinal  cord  is  composed 
of  fibers,  nerve-cells,  neuroglia,  and  blood-vessels.  In  the  white  sub- 
stance there  are  found  only  nerve-fibers  and  neuroglia;  in  the  gray 
substance,  nerve-cells  and  fibers  plunged  in  a  stroma  of  neuroglia. 

White  Substance. — The  white  matter  is  composed  principally 
of  m.edulJated  fibers  without  the  sheath  of  Schwann.  The  fibers  in 
the  white  substance  are,  for  the  most  part,  arranged  longitudinally ; 
those  which  pass  to  the  nerve-roots,  as  well  as  those  fibers  which  pro- 
ceed from  the  gray  matter  into  the  columns,  possess  an  oblique 
course.  In  addition  there  are  decussating  fibers  in  the  white  com- 
missure. 

On  cross-section  the  fibers  (which  are  of  different  sizes)  present 
the  appearance  of  small  circles  with  a  rounded  dark  spot  in  their 
centers.     This  latter  represents  the  axis  cylinder  of  the  fiber. 

The  diameter  of  the  fibers  varies  from  ^/-,ooo  to  ^/i2oo  inch. 
The    most   voluminous    are   the    motor   parts   of    the    antero-Iateral 


542  PHYSIOLOGY. 

column  and  direct  cerebellar  tract;  the  finest  are  in  the  pos- 
terior median  column. 

Classification. — The  fibers  of  the  cord  are  classified  into  two 
great  classes:   intrinsic  and  extrinsic. 

Intrinsic. — This  class  of  fibers  originates  in  and  terminates  in 
the  cord,  thereby  uniting  the  levels  of  gray  matter.  Fixed  by  their 
lower  extremities  upon  a  given  point  of  gray  substance,  they  follow 
an  ascending  course,  to  become  lost  by  their  extremities  in  a  more  or 
less  elevated  part  of  the  gray  column.  Thus  they  are  fibers  of  union 
or  association  for  the  purpose  of  establishing  communication  between 
the  different  levels  of  the  gray  substance  of  the  cord. 

Extrinsic. — These  fibers  in  the  gray  matter  proceed  to  the  gan- 
glia of  the  brain  after  having  traversed  the  medulla  oljlongata,  pons, 
and  crura.  They  unite  the  cells  of  the  gray  substance  of  the  spinal 
cord  to  the  upper  nerve-centers.  They  are  long  and  gradually 
diminish  in  number  from  the  top  to  the  bottom  of  the  cord. 

Degeneration  occupies  their  whole  extent.  Some  are  centripetal 
and  undergo  an  ascending  degeneration.  They  are  contained  in  the 
column  of  Goll,  the  direct  cerebellar  bundle,  and  Gowers's  tract. 
The  others  are  centrifugal  fibers,  and  undergo  a  descending  degen- 
eration. They  are  localized  in  the  crossed  pyramidal  and  bundle  of 
Tiirck.     They  are  the  last  ones  to  appear  in  the  fcetus. 

The  roots  of  the  nerves  arrive  at  the  central  gray  substance  and 
plunge  into  it  after  having  passed  between  the  fibers  of  the  peri- 
pheral white  sul)stance.  But  few  of  them  take  part  in  the  constitu- 
tion of  the  cortical  white  matter. 

Neuroglia. — In  addition  to  the  fibers  just  discussed  the  white 
matter  of  the  cord  contains  neuroglia.  From  the  neuroglia  project 
extremely  fine  prolongations.  These  penetrate  the  cord  to  form 
within  its  thickness  an  infinity  of  partitions  of  extreme  thinness. 
These  are  united  to  the  adventitious  tissue  of  the  vessels  and  to  the 
tissue  w^hich  serves  as  a  basement  membrane  to  the  epithelium  of 
the  ependyma.  Thus  there  is  formed  (on  transverse  section)  a  poly- 
gonal network  whith  isolates  little  colonies  of  nerve-elements  one 
from  the  other.  This  sort  of  framework  has  been  compared  to  a 
sponge  in  whose  interstices  are  found  the  fibers  and  cells  of  the  cord. 

ISTeuroglia  does  not  belong  to  the  category  of  connective  tissues. 
It  is  a  special  formation  which  is  derived  from  the  primitive  epiblast. 
In  the  central  gray  substance  the  neuroglia  does  not  seem  to  be  any 
more  than  amorphous  matter  with  some  few  cellular  elements.  The 
gelatinous  substance  of  Eolando  is  composed  of  abundant  neuroglia 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.  543 

in  the  form  of  amorphous  matter.  The  only  connective  tissue  pres- 
ent in  the  cord  is  carried  in  by  the  blood-vessels. 

Gkay  Matter  of  the  Cord. — The  gray  substance  of  the  cord 
is  composed  of  neuroglia,  fibrils,  and  nerve-cells. 

The  cells  of  the  cord  are  formed  by  a  small  mass  of  protoplasm 
in  which  is  plunged  a  nucleus  surrounded  by  pigment-granules. 
These  cells,  whose  volume  varies  with  the  groups,  have  a  certain 
number  of  prolongations. 

Cell-arrangement. — The  cells  of  the  cord  are  not  disseminated 
in  the  gray  substance  in  a  disorderly  way.  They  are  grouped  at  cer- 
tain points  to  form  nuclei — nuclei  of  nerves ;  these  are  situated  one 
above  the  other  in  a  fashion  to  form  columns  parallel  with  the  long 
axis  of  the  cord. 

There  are  distinguished  three  groups  in  the  anterior  horns:  an 
interior  internal  group,  an  anterior  external  group,  and  a  posterior 
external  group. 

In  the  posterior  horns  the  cells  are  fewer  in  number;  it  is  only 
at  the  internal  part  of  the  neck  of  these  horns  that  there  is  found  a 
grouping.  It  is  known  as  the  dorsal  nucleus  of  Stilling  or  the  vesi- 
cular  column  of  Clarke. 

The  ganglionic  cells  of  the  aJiterior  horns  are  very  large,  star- 
shaped,  and  from  ^/^^o  to  Voqo  inch  in  diameter.  That  is,  they  are 
nearly  large  enough  to  be  visible  to  the  naked  eye. 

Degeyicration. — The  nuclei  of  origin  of  the  anterior  roots  are 
seized  with  degeneration  in  the  various  forms  of  muscular  atrophy. 
The  cells,  by  reason  of  their  function,  are  known  as  motor  cells.  They 
are  motors  for  the  muscles  to  which  their  nerves  go,  and  trophic  for 
the  same  nerves  and  muscles.  Progressive  muscular  atrophy  is  ana- 
tomically cliaracterized  by  a  general  atrophy  of  the  motor  cells  of  the 
anterior  horns  of  the  cord.  Children's  palsy  is  also  characterized  by 
atrophy  of  these  cells. 

The  cells  of  the  posterior  horns,  irregularly  distributed  in  the 
neuroglia,  are  fewer  in  number  and  smaller  in  size  than  are  those  of 
the  anterior  horns.     Their  diameters  average  about  V1200  inch. 

Anatomically,  the  column  of  Clarke  exists  only  from  the  second 
lumbar  to  the  eighth  dorsal  pair  of  nerves.  However,  there  are  small, 
erratic  groups  of  cells  and  two  restiform  nuclei  at  the  level  of  the 
medulla  which  are  analogous  to  the  two  columns  of  Clarke.  The  cells 
of  the  column  of  Clarke  are  very  large,  star-shaped,  and  only  very 
meagerly  branched. 

The  intermedio-lateral  gray  column  is  in  the  outermost  portion  of 


544  PHYSIOLOGY. 

gray  matter,  midway  between  the  anterior  and  posterior  horns.  It 
lies  in  what  is  known  as  the  lateral  horn.  It  is  the  spinal  origin  of 
the  great  sympathetic.  A  part  of  the  posterior  root-fibers  are  said 
to  end  in  these  columns.  Erom  this  as  a  source  fibers  pass  into  the 
column  of  Goll  and  the  direct  cerebellar  tract;  others  pass  into  the 
columns  of  Burdach  and  Gowers. 

To  the  degenerative  changes  within  the  cells  of  the  column  of 
Clarke  have  been  attributed  the  vasomotor  troubles  of  paralysis  agi- 
tans.  Sclerosis  of  the  lateral  columns  explains  the  exaggerated 
trembling  in  the  reflexes. 

The  fibers  of  the  cells  of  the  gray  matter  form  a  spongy  sub- 
stance which  unites  the  two  halves  of  the  gray  axis  of  the  cord  to  one 
another.  This,  the  gray  commissure,  passes  in  front  of  and  behind 
the  central  canal  of  the  cord. 

Neuroglia. — The  neuroglia  of  the  gray  matter  has  a  structure 
analogous  to  that  of  the  neuroglia  of  the  white  substance  of  the  cord. 
It  is  found  in  particular  abundance  at  the  extremity  of  the  posterior 
horns  (gelatinous  substance  of  Rolando)  and  at  the  periphery  of  the 
central  canal. 

The  Central  Canal. — This  is  a  canal  of  very  fine  caliber  located 
within  the  center  of  the  gray  commissure.  It  transverses  the  entire 
length  of  the  cord,  and,  at  the  level  of  the  nib  of  the  calamus  scrip- 
torius,  is  continuous  with  the  fourth  ventricle ;  by  means  of  the  latter 
it  communicates  with  the  ventricles  of  the  brain. 

The  wall  of  this  canal,  known  as  the  ependyma,  is  composed — 
from  within  outward — of:  (1)  a  ciliated  epithelium,  (3)  an  amor- 
phous basal  membrane,  find  (3)  a  substratum  of  neuroglia  which 
unites  the  wall  of  the  canal  to  the  body  of  the  cord.  Tlie  canal  is 
flanked  on  each  side  by  a  longitudinal  vein;  the  two  constitute  the 
central  veins. 

Systemization  in  the  Spinal  Cord. — The  spinal  cord  may  be  con- 
sidered as  formed  of  a  series  of  segments  superposed.  They  are 
metameres  corresponding  to  each  pair  of  spinal  nerves.  Each  one  of 
these  is  a  complete  center,  being  supplied  with  nerve-cells  and  motor 
and  sensory  nerves.  Each  one  is  different  from  its  neighbor,  since  it 
innervates  a  particular  area  of  the  surface  of  the  body,  whether  it  be 
tactile  surface  or  muscular  group. 

The  nerve-cells  are  grouped  in  motor  and  sensory  fields.  They 
are  all  in  perfect  communication  with  one  another  by  reason  of 
numerous  fibers;  some  are  longitudinal  {longitudinal  commissures) 
which  unite  the  various  levels  of  the  cord;    others  are  transverse 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.  545 

{transverse  commissures)  whose  function  seems  to  be  to  unite  the 
cells  of  the  right  side  to  those  of  the  left  side  of  each  segment.  The 
transverse  commissures  are  but  from  one  to  three  centimeters  in 
extent. 

In  addition  to  the  spinal  commissures  just  mentioned  there  are 
two  other  kinds  formed  by  the  long  fibers  uniting  the  spinal  cord 
either  to  the  cerebrum  or  cerebellum.  They  are  known  as  the 
cerehro-spinal  and  cerehello-spinal  fibers. 

Experimental  physiology,  pathological  anatomy,  and  oml)ryology 
all  agree  very  admirably  in  demonstrating  that  the  apparently  homo- 
geneous cord  is  composed  of  distinct  and  specialized  parts.  These 
parts  are  called  systems,  which,  in  the  white  substance,  form  sec- 
ondary columns,  or  bundles. 

White  Columns  of  the  Cord. 

Flechsig  ascertained  that  in  the  foetus  the  different  bundles  of 
nerve-fibers  did  not  all  take  on  myelin  layers  at  the  same  time.  By 
taking  advantage  of  this  fact  he  was  able  to  trace  the  bundles  of  fibers 
with  myelin  and  thus  map  out  the  different  tracts  of  the  spinal  cord 
and  brain.  Gudden  extirpated  an  organ  of  sense  and  after  waiting 
a  sufficient  length  of  time  was  able  to  trace  the  course  of  the  atro- 
phied nerve-fibers. 

The  nerve-filiers  of  the  cord  enveloping  the  central  gray  axis  are 
distributed  in  different  bundles  or  columns.  These  have  previously 
been  mentioned  cursorily,  but  will  now  be  discussed  in  detail. 

Anterior  Column. — The  anterior  column  comprises  that  area  be- 
tween the  anterior  median  groove  and  the  line  of  implantation  of  the 
anterior  roots  of  the  spinal  nerves.  Its  most  internal  fibers  are  com- 
missural ;  they  cross  throughout  the  whole  extent  of  the  cord  and  so 
contribute  in  the  formation  of  the  white  commissure.  Other  fibers 
run  across  at  the  same  level  to  connect  the  large  cells  of  the  anterior 
horns  of  the  two  halves  of  the  spinal  cord. 

The  anterior  column  comprehends  two  bundles :  one,  internal 
(next  to  the  median  groove),  is  known  as  TilrcTc's  bundle,  or  direct 
pyramidal  bundle;  the  other,  external,  comprises  the  remainder  of 
the  anterior  column  and  is  known  as  the  root-bundle  of  the  anterior 
column,  or  antero-lateral  ground-bundle. 

The  bundle  of  Tiirck  (pyramidal  bundle,  direct  cerebral,  direct 
motor)  is  formed  of  centrifugal  fibers  which  descend  from  the  brain 
into  the  cord  without  decussating  at  the  level  of  the  medulla  ob- 
longata.    Its  fibers  are  longitudinal  and  travel  along  and  through 

35 


546 


PHYSIOl.Or.Y. 


the  brain,  the  anterior  pyramid  of  the  medulla  and  the  same  side 
of  the  corresponding  half  of  the  spinal  cord.  Yet,  having  arrived 
in  the  cord,  some  of  its  fibers  cross  to  the  opposite  side  along  the  path 
of  the  white  commissure.  They  finally  terminate  in  the  cells  of  the 
anterior  cornua.  This  bundle  usually  terminates  about  the  second 
lumbar  nerve.     It  undergoes  descending  degeneration. 

The  antero-lateral  ground-bundle  (root-bundle  of  the  anterior 
column)  occupies  the  territory  between  the  preceding  and  the  antero- 
lateral groove.     It  is  formed   in  ]-)art  by  the  anterior  roots  which 


ax 


<f:cn 


Fig.  237. — Transverse  Section  of  the  Spinal  Cord. 

T.  D.,  Burdach's  tract.  T.  G.,  GoH's  tract.  T.  P.  C,  Crossed  pyramidal 
tract.  T.  C.  D.,  Direct  cerebeHar  tract.  G..  T..  Gower's  tract.  T.  P.  D.,  Direct 
pyramidal  tract,  or  Tiirck's.  T.  L.  P.,  Deep  lateral  tract.  Straight  lines  are 
motor  tracts.  Little  crosses  are  sensory  tracts.  Dotted  spaces  are  cerebellar 
tracts.     T.  I.,  T.  R.,  Root  tracts. 

descend  in  a  certain  course  within  its  interior;  but  especially  by  the 
more  or  less  long,  longitudinal  fibers.  The  latter  unite  between 
themselves  the  successive  levels  of  the  anterior  horns.  It  is  thus  in 
part  a  system  of  longitudinal  commissural  fibers. 

The  anterior  ground-l)undle  is  continued  beneath  the  floor  of  the 
fourth  ventricle  in  the  superior  longitudinal  bundle,  and  ends  in 
the  gray  matter  of  the  third  ventricle,  giving  off  collaterals  to  the 
nuclei  of  the  oculo-motor,  pathetic,  and  abducent. 

Lateral  Column. — The  lateral  column  is  bounded  between  the 
line  of  implantation  of  the  anterior  roots  and  the  line  of  insertion 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.  547 

of  the  posterior  roots.     It  is  formed  of  fibers  which  are  larger  on  the 
surface  and  much  finer  in  the  depths. 

\  This  column  comprises  -jive  different  systems  of  bundles.  They 
are:  (1)  the  direct  cerebellar;  (2)  the  bundle  of  Gowers,  or  ascend- 
ing antero-hiteral-ccreheUar  tract;  (3)  the  crossed  pyramidal  tract; 
(4)  veslihulo-spinal  tract;  (5)  deep  lateral,  or  lateral  marginal,  zone. 
The  direct  cerebellar  bundle,  or  tract,  is  situated  at  the  posterior 
and  superficial  part  of  the  lateral  column  in  the  form  of  a  very  thin 
band.  It  extends  from  the  second  lumbar  upward  to  the  restiform 
bodies,  into  the  vermis  of  the  cerel^ellum.  It  is  formed  of  a  collec- 
tion of  centripetal  fibers  which  unite  the  cerebellum  to  different 
levels  of  the  vesicular  column  of  Clarke.  It  develops  ascending  de- 
generation. About  the  cells  of  Clarke  arl)orize  the  collaterals  of  the 
posterior  root  so  that  there  is  an  indirect  communication  between  the 
posterior  roots  and  the  cerebellum. 

The  bundle  of  Gowers,  or  ascending  antero-lateral  tract,  occupies 
the  anterior  superficial  zone  of  the  lateral  column.  This  bundle  com- 
mences at  its  inferior  part  in  the  lumbar  swelling,  increasing  in  size 
as  it  ascends  l)y  two  orders  of  roots,  some  fine,  others  large.  It  termi- 
nates by  its  fine  fibers  in  the  lateral  nucleus  of  the  medulla;  by  its 
larger  fibers  in  the  cerebellum  by  way  of  the  superior  peduncle.  This 
tract  undergoes  ascending  degeneration. 

The  crossed  pyramidal  tract  (motor  tract  or  cereljral  crossed 
tract)  is  situated  inside  the  cerebellar  tract.  The  term  has  been 
applied  to  that  which  is  contained  within  the  pyramids  of  the 
medulla,  and  which  decussates  at  this  level  with  the  opposite  tract. 
It  decreases  in  volume  from  above  downward  to  terminate  in  from 
the  second  to  the  fourth  luml)ar  pair. 

It  is  composed  of  long,  centrifugal  fillers  which  unite  the  motor 
regions  of  the  cortex  of  the  brain  with  the  motor  cells  of  the  anterior 
horns  of  the  cord.  It  undergoes  descending  degeneration  as  the  re- 
sult of  lesi(ms  which  seize  the  cortex,  internal  capsule,  or  cerebral 
peduncle. 

A  lesion  of  the  pyramidal  tract  in  the  cord  produces  monoplegia 
below  the  lesion  and  on  the  same  side.  Its  degeneration,  as  a  result 
of  lesion  of  the  brain,  gives  place  to  a  crossed  hemiplegia,  whose 
clinical  mark  is  a  spasmodic  contracture. 

It  is  well  to  remember  that  there  is  a  double  decussation  of  the 
motor  fibers :  one  at  the  level  of  the  neck  of  the  medulla  oblongata, 
the  other  much  lower — the  length  of  the  white  commissure.  From 
this  the  student  can  comprehend  why  in  the  majority  of  hemiplegias 


548  PHYSIOLOGY. 

the  non-paralyzed  member  has,  nevertheless,  lot^t  its  muscular  energy; 
also  why  a  unilateral  cerebral  lesion  is  al)le  to  cause  })ermanent  con- 
tracture of  the  two  inferior  members  or  an  exaggeration  of  the  re- 
flexes of  tile  side  not  paralyzed. 

The  vestibulo-spmal  tract  runs  from  the  vestibuhir  nucleus, 
which  contains  Deiters's  nucleus,  and  descends  in  the  antero-lateral 
columns,  arborizing  about  the  anterior  horns.  This  tract  is  connected 
with  the  nucleus   fastigii  of  the   cerebellum. 

The  deep  lateral  tracts,  lateral  mixed  tract,  or  lateral  marginal 
zone,  is  molded  upon  the  lateral  concavity  of  the  gray  matter.  It 
incloses  at  the  same  time  the  fibers  coming  from  the  anterior  motor 
horns,  the  gray  column  of  Clarke,  and  the  gray  intermedio-lateral 
column. 

The  lateral  ground-bundle  is  continued  in  the  posterior  longi- 
tudinal bundle  and  ends  in  the  posterior  corpora  quadrigemina. 
The  posterior  longitudinal  bundle  puts  the  sensory  bulbar  nuclei  and 
the  tubercula  quadrigemina  in  communication  with  the  nuclei  of  the 
motor  nerves  of  the  eyes  and  the  motor  nerves  of  the  trunk. 

Posterior  Columns. — The  posterior  columns  comprise  that  area 
of  the  spinal  cord  lying  between  the  postero-lateral  groove  and  the 
posterior  median  groove.  It  is  composed  of  fine  fibers  in  that  por- 
tion nearest  the  median  groove,  and  is  remarkable  for  its  abundance 
of  neuroglia. 

This  large  tract  is  divided  into  two  tracts:  one  internal,  the 
other  external. 

The  internal  one,  or  column  of  Goll,  is  especially  apparent  in 
the  upper  part  of  the  cord.  Here  it  occurs  in  the  form  of  a  trian- 
gular pyramid  whose  base  is  turned  toward  the  central  gray  com- 
missure. It  is  formed  by  long  commissural  fibers  which  arch  so  as 
to  unite  the  posterior  horns.  It  proceeds  from  the  level  of  one  pos- 
terior horn  to  that  of  a  higher  level.  It  incloses  the  posterior  root- 
fibers  which  compose  the  major  portion  of  it.  The  fibers  of  Goll  are 
very  long,  ascending  from  the  cauda  equina  to  Goll's  or  gracilis 
nucleus  of  this  tract  in  the  medulla.  Its  trophic  centers  are  in  the 
cells  of  the  ganglion  of  the  posterior  root. 

The  more  external  and  cuneiform  tract,  rohimri  of  Bvrdacli,  con- 
tains short,  commissural,  longitudinal  fhers  which  have  the  same  dis- 
tribution as  those  of  Goll,  and  sensory  fibers,  which  also  spring  from 
the  posterior  horns,  but  do  not  sojourn  there.  Almost  immediately 
they  pass  into  the  mixed  lateral  column  of  the  same  side,  or,  travers- 
ing the  commissure,  cross  into  the  opposite  tract.     At  the  level  of 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.  549 

the  medulla  oblongata  these  fibers  go  to  form  the  lemniscus,  or  fillet, 
which  itself  terminates  in  the  corpora  qiiadrigemina,  the  optic 
thalami,  and  the  sensory  convolutions.  In  transverse  section  of  this 
colmnn  there  is  ascending  degeneration. 

The  comma  tract  is  composed  of  a  few  fibers  in  the  column  of 
Burdach.  After  lesions  of  the  cord  they  undergo  descending  degen- 
eration. These  fibers  originate  from  the  descending  fibers  of  the 
posterior  roots. 

11 


Fig.  2.38. — Section  of  Spinal  Cord,  Showing  the  Less  Well-known  Tracts. 

1,  Comma  tract.  2,  Lissauer's  tract.  3,  Monakow's  prepyramidal  or  rubro- 
spinal tract  from  nucleus  ruber  down  lateral  column  to  anterior  horn.  4,  Ves- 
tibulo-spinal  tract  from  vestibular  nucleus  down  to  anterior  horn.  5,  Sulco- 
marginal tract  from  corpora  quad.  6,  Anterior  marginal  bundle  from  nucleus 
fastigii.  7,  Helweg's  bundle  from  olivary  body.  8,  Anterior  root.  10,  Posterior 
root.     9,   Oval  bundle.     11,   Septo-marginal. 

The  posterior  columns,  and  particularly  the  columns  of  Burdach, 
are  the  seat  of  the  sclerosis  known  as  tahes  dorsalis,  or  locomotor 
ataxia.  Clinically  this  disease  is  characterized  by  progressive  aboli- 
tion of  co-ordination,  loss  of  equilibrium,  paralysis  of  eye-muscles, 
loss  of  tendon  reflexes,  etc. 

Tracts  of  Lissauer. — About  the  entrance  of  the  posterior  roots 
into  the   postero-lateral  groove   of   the  cord  are  found   two   small. 


550  PHYSIOLOGY. 

cuneiform  columns.  They  are  ilu;  root-zones  of  Lissauer.  The  one 
is  internal,  the  other  external.  The  two  zones  are  formed  by  the 
posterior  root-fibers  at  their  entrance  into  the  cord.  They  have  the 
same  properties  as  the  posterior  roots  and  undergo  ascending  degen- 
eration under  the  same  conditions  that  produce  it  in  the  latter. 

Degeneration. 

Descending  Degeneration. — The  crossed  pyramidal,  the  direct 
pyramidal,  the  vestibulo-spinal,  the  comma  tract. 

Ascending  Degeneration. — Goll's,  Burdach's,  Gowers'  (ascending 
antero-lateral  cerebellar),  direct  cerel)ellar,  Lissauer's  tract. 

Roots  of  Nerves. 

The  spinal  nerves,  thirty-one  pairs  in  number,  exist  throughout 
the  entire  length  of  the  cord. 

The  anterior  root-fibers  are  composed  of  large  nerve-tubes  which 
lose  themselves,  for  the  most  part,  in  the  ganglionic  cells  of  the 
anterior  horns  of  the  same  or  opposite  sides. 

The  posterior  root-fihers  are  composed  of  fine  tubes.  After  hav- 
ing arisen  in  the  intervertebral  ganglia  they  go  toward  the  postero- 
lateral groove,  where  they  enter  the  cord.  There  are  here  two  groups 
of  fibers:    one  external,  the  other  internal. 

The  external  root-fibers  penetrate  into  the  gelatinous  substance 
of  Eolando,  where  they  become  ascending.  After  a  more  or  less 
lengthy  course  they  pass  into  the  ganglionic  cells  of  the  posterior 
horn. 

The  internal  root-fibers,  which  pass  into  the  posterior  column, 
become  lost  either  in  the  cells  of  the  posterior  horn  or  in  the  vesi- 
cular column  of  Clarke.  Some  very  long  fibers  ascend  to  the  nuclei 
of  Goll  and  Burdach  in  the  medulla,  where  they  terminate. 

Some  of  the  fibers  traverse  the  posterior  commissure  to  pass 
either  into  the  anterior  horn  of  the  opposite  side  (and  act  in  reflex 
motor  actions)  or  into  the  posterior  horn  or  descend  in  the  cord  as 
fibers  of  the  comma  tract. 

Commissures  of  the   Cord. 

The  white,  anterior  commissure  is  formed  by  a  body  of  fibers 
which  decussate  upon  the  median  line  to  pass  into  the  lateral  half 
of  the  cord  opposite  to  that  from  which  they  came.  It  forms  the 
major  portion  of  the  fibers  of  the  direct  pyramidal  tract.     This  tract 


AXATOMY  AND  PHYSIOLOCxY  OF  NERVOUS  SYSTEM. 


551 


in  its  long  course  in  the  cord  gives  off  fibers  in  succession  which  go 
either  into  the  cells  of  the  anterior  horn  or  into  the  crossed  pyra- 
midal tract  of  the  opposite  side.  The  commissure  also  contains 
fibers  which  unite  transversely  the  anterior  horns  of  the  two  sides. 

The  gray,  or  posterior,  commissure  is  likewise  formed  by  decussa- 
tions upon  the  median  line  both  in  front  of  and  back  of  the  central 
canal.  The  fibers  comprising  this  decussation  are:  some  of  the 
fibers  from  the  posterior  roots  on  one  side  to  terminate  in  the 
opposite  posterior  horn;  also,  fibers  of  the  posterior  horn  which  go 
into  the  deep  lateral  tract. 


Fig.    2.30. — Medulla    Oblongata,    Pons,    Cerebellum,    and    Pes    Pedunculi. 
Anterior  View,  to  Demonstrate  Exits  of  Cranial  Nerves.      (Edingeb.  1 

Medulla  Oblongata. 

The  medulla  oblongata  is  a  continuation  of  the  spinal  cord 
which  crowns  its  upper  part  in  the  form  of  a  capital.  It  reaches 
from  the  cord  to  the  pons  Varolii.  The  medulla  is  an  enlargement 
in  the  form  of  a  truncated  cone,  a  little  flattened  from  before  back- 
ward. It  measures  an  inch  in  length,  about  three-fourths  in  width, 
and  about  one-half  inch  in  thickness.  Commencing  toward  the  mid- 
dle part  of  the  odontoid  process,  it  inclines  forward,  to  recline  upon 
the  basilar  process  of  the  occipital  bone.  The  medulla  forms  with 
the  cord  an  obtuse  angle  open  in  front. 


552 


PHYSIOLOGY. 


The  back  and  sides  of  the  medulla  arc  embraced  by  the  cere- 
helluin.  In  front,  the  medulla  is  bounded  anteriorly  by  the  pons 
Varolii,  posteriorly  by  a  transverse  line  which  unites  the  lateral 
angles  of  the  fourth  ventricle  to  divide  its  floor  into  two  triangles. 

The  anterior  and  posterior  median  fissures  of  the  cord  are  con-, 
tinned  up  into  the  medulla.  The  anterior  fissure  becomes  some- 
what indistinct  at  one  point  by  reason  of  the  decussation  of  the 
bundles  forming  the  pyramids.  The  posterior  median  fissure  termi- 
nates at  the  lower  end  of  the  fourth  ventricle.  The  weight  of  the 
medulla  is  about  one  hundred  grains. 


Fig.  240. — The  Three  Pairs  of  Cerebellar  Peduncles.      (After 

HiRSCHFELD   and   LEVEILLft.) 

1,  Fossa  rhomboidalis.  2,  Striae  acusticae.  3,  Posterior  cerebellar  peduncle. 
5,  Anterior  cerebellar  peduncle.  6,  Fillet.  7,  Middle  cerebellar  peduncle,  or 
Brachium  pontis.     8,  Corpora  quadrigemina. 

From  the  front  and  sides  of  the  medulla  arise  the  sixth  to  the 
twelfth  cranial  nerves,  inclusive. 

External  Form  of  the  Medulla  Oblongata. — Inspection  of  the 
inferior  surface  of  the  medulla  first  brings  to  view  along  the  median 
line  the  anterior  median  groove.  This^  as  before  mentioned,  is  a 
continuation  of  a  similar  groove  belonging  to  the  cord.  Tn  one  area 
the  crossing  of  the  white  fibers  from  side  to  side  (decussation  of  the 
pyramids)  renders  this  more  shallow.  At  the  base  of  the  groove  is 
seen  a  continuation  of  the  white,  anterior  commissure  of  the  cord. 
This  layer  unites  the  two  pyramids  of  the  medulla  and  is  known  as 
the  raphe  of  Stilling. 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.  553 

AxTERioR  Pyramids. — On  each  side  of  the  median  groove  are 
located  two  white  columns,  which  are  slightly  swollen  at  their  upper 
ends  and  have  the  appearance  of  clubs.  These  columns  are  the 
anterior  pyramids. 

Olives. — Just  outside  of  the  upper  portion  of  the  pyramids  are 
two  prominent,  oval  masses  whose  longer  axes  are  vertical.  These 
bodies  measure  about  one-half  inch  in  length  and  one-fourth  in 
breadth.  They  are  the  inferior  olives.  They  are  prominences  added 
to  the  medulla,  and  do  not  have  any  similar  portions  in  the  spinal 
cord.  The  olives  are  separated  from  the  pyramid  in  front  by  a 
groove;  in  this  latter  is  embodied  the  continuation  of  the  false 
antero-lateral  groove.  In  it  is  found  the  apparent  origin  of  the 
hypoglossal  nerve.  Behind,  the  olives  are  separated  from  the  resti- 
f orm  bodies  by  another  groove :  a  continuation  of  the  postero-lateral 
groove  of  the  spinal  cord.  From  it  emerge  the  glosso-pharyngeal, 
the  vagus,  and  the  spinal  accessory.  At  their  lower  edge  these 
grooves  are  somewhat  effaced  by  the  white  arcuate  fibers  of  the  olive ; 
these  latter  ascend  in  the  restiform  bodies. 

Eestiform  Body. — Back  of  the  postero-lateral  groove  of  the 
medulla,  and  therefore  on  its  posterior  surface,  is  found  a  large 
column  of  white  substance :  the  restiform  body.  It  seems  to  be  con- 
tinuous below  with  the  posterior  columns  of  the  cord;  above  with 
the  inferior  peduncle  of  the  cerebellum.  These  columns  form  part 
of  the  anterior  as  well  as  lateral  aspects  of  this  organ. 

Posteriorly  it  is  seen  that  the  inferior  third  of  the  medulla  is 
very  different  from  the  upper  two-thirds.  The  inferior  third  is 
similar  to  the  cord  in  that  it  possesses  a  posterior  median  groove 
continuous  with  that  of  the  cord;  on  each  side  of  it  are  two  white 
columns.  They  are  continuations  of  the  posterior  columns  of  the 
cord. 

At  the  base  of  the  groove  is  found  the  gray  commissure. 

In  the  upper  two-thirds  of  the  medulla  this  form  is  much 
changed.  Here  the  posterior  columns  take  the  name  of  restiform 
bodies,  or  inferior  peduncles  of  the  cerebellum.  Instead  of  pursuing 
a  parallel  course,  they  diverge  from  one  another  in  such  a  manner 
as  to  leave  between  them  at  their  upper  end  a  V-shaped  surface. 
The  surface  included  within  this  angular  space  comprises  gray  mat- 
ter. It  forms  the  lower  half  of  the  floor  of  the  fourth  ventricle. 
The  upper,  angular  portion  is  formed  by  the  posterior  face  of  the 
pons. 

The  beginning  of  divergence  of  the  restiform  bodies  presents 


554 


PHYSIOLOGY. 


Fig.    241. — Metencephalon,    Mesencephalon,    and    Thalamencephalon, 
from  the  Dorsal  Surface.     (Gokdinier,  after  Obersteiner.) 

1,  Anterior  cornu  of  lateral  ventricle.  2,  Fifth  ventricle.  3,  Septum  luci- 
dum.  4,  Anterior  pillars  of  fornix.  5,  Taenia  semicircularis.  6,  Anterior  com- 
missure. 7,  Third  ventricle.  8,  Middle  commissure.  9,  Sulcus  choroideus.  10, 
Nates.  11,  Corpus  geniculatum  internum.  12,  Lateral  groove  of  mesencepha- 
lon. 13,  Pons.  14,  Conductor  sonorus.  15,  Sulcus  longitudinalis  medianus. 
16,  Trigonum  hypoglossi.  17,  Corpus  restiforme.  18,  Clava.  19,  Posterior  fis- 
sure. 20,  Sulcus  paramedianus  dorsalis.  21,  Sulcus  lateralis  dorsalis.  22,  Lateral 
column.  23,  Funiculus  cuneatus.  24,  Funiculus  gracilis.  25,  Tuberculum  cune- 
atum.  26,  Ala  cinerea.  27,  Tuberculum  acusticum.  28,  Eminentia  teres.  29, 
Lingula.  30,  Frenulum  veil.  31,  Testis.  32,  Sulcus  corp.  quad,  longitudinalis. 
33,  Pineal  body.  34,  Pedunculus  conarii.  35,  Stria  pinealis.  36,  Optic  thala- 
mus.   37,  Foramen  of  Monro.    38,  Caudate  nucleus.    39,  Corpus  Callosum. 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM. 


555 


an  appearance  analogous  to  that  of  a  writing  pen;  hence  its  name: 
calamus  scriptorius.  Tlie  space  between  the  restiforni  bodies  pre- 
sents a  median  groove.  Above  it  passes  over  tlie  posterior  face  of 
the  pons ;  below  it  is  arrested  by  the  point  of  divergence  of  the  resti- 
forni bodies.  This  is  known  as  the  groove  of  the  calamus  scriptorius. 
From  each  side  of  this  groove  there  proceed  white  transverse  fibers 
whose  direction  is  at  right  angles  to  that  of  the  groove.  They  are 
known  as  the  harhoi  of  the  calamus,  or  auditory  strice.  These  fibers 
are  the  posterior  roots  of  the  auditory  nerve. 


14 

Fig.  242. — Diagrammatic  Transverse  rSection  of  the  Spinal  Bulb  X  3, 
at  about  the  middle  of  the  olivary  body,  to  illustrate  the  principal 
nuclei  and  tracts  at  that  level.     (Waller,  after  Schwalbe.) 

1,  Nucleus  cuneatus.  2,  Nucleus  gracilis.  3,  Vagus  nuclei.  4,  Hypoglossal 
nucleus.  5,  Funiculus  teres.  6,  Funiculus  sclitarius.  7,  Funiculus  gracilis. 
S,  Funiculus  cuneatus.  9,  Restiform  tract.  10,  Substantia  gelat.  Ro.  11,  Spinal 
root  of  fifth  nerve.  12,  Antero-lateral  nucleus.  13,  Olivary  body.  14,  Anterior 
pyramid. 


The  restiform  bodies,  which  seem  to  form  the  limits  of  the  floor 
of  the  fourth  ventricle  on  each  side  of  the  calamus  scriptorius,  come 
up  from  the  posterior  columns  of  the  cord.  They  ascend  upward 
and  outward  toward  the  cerebellum. 

The  columns  of  Goll  and  Burdach  of  the  spinal  cord  as  they 
enter  the  lower  portion  of  the  posterior  aspect  of  the  medulla  seem 
to  be  divided  into  several  distinct  tracts.  Bordering  upon  the  pos- 
terior median  fissure  is  the  column  of  Goll.  As  the  tract  approaches 
the  fourth  ventricle  it  broadens  out  to  form  the  expansion  knowTi  as 
the  clava.  The  two  clavffi  diverge  to  form  the  nib  of  the  calamus 
scriptorius. 


556 


PHYSIOLOGY. 


Lying  external,  but  adjacent,  to  tlie  column  of  Goll  is  another 
tract  which  is  a  continuation  of  tlie  column  of  Burdach.  It  is  the 
funiculus  cuneaiiLs. 

As  previously  stated,  the  upper,  expanded  portion  of  the  gracilis 
nucleus  has  been  termed  the  clava ;  the  upper  portion  of  the  cuneatus 
is  known  as  the  cuneate  tubercle.  Both  prominences  are  caused  by 
underlying  masses  of  gray  matter. 

The  scriptoria!  half  of  the  floor  of  the  fourth  ventricle  is  divided 
into  two  lateral  halves  by  a  longitudinal  groove.     In  each  half  can 


Fig.   243. — Cross-section  of   the   Oblongata   through   the  Decussation   of 
the  Pyramids.      (After  Hekle. ) 

Fpy,  Pyramidal  tract.  Cga,  Anterior  horn.  Fa',  Remnant  of  anterior 
column.  Ng,  Nucleus  funiculi  gracilis,  g,  Substantia  gelatinosa.  XI,  Nervus 
accessorius. 


be  seen  three  small  prominences  whose  general  shape  is  somewhat 
triangular.  The  first  one,  a  triangle  of  white  color,  is  the  trigonum 
hypoglossi;  it  covers  the  nucleus  of  origin  of  the  hypoglossus  nerve. 
The  second  one,  trigonum  vagi  and  the  continuation  of  the  head  of 
the  anterior  horn,  corresponds  to  the  nuclei  of  the  ninth,  tenth,  and 
eleventh  cranial  nerves.  It  is  the  aJa  cinerea.  The  third  eminence, 
the  trigonum  acustici.  covers  the  nucleus  of  the  eighth  nerve. 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.  557 

Internal  Structure  of  the  Medulla. — The  medulla  oblongata,  like 
the  spinal  cord,  is  formed  of  nerve-cells,  nerve-fibers,  and  a  mesh- 
work  of  neuroglia.  As  it  is  a  continuation  of  the  cord,  one  ought 
to  find  the  white  columns  and  central  axis  common  to  the  spinal 
cord.  As  a  matter  of  fact,  the  constituent  elements  of  the  cord  ane 
found  in  the  medulla,  but  their  position  is  changed  very  much.  The 
cells  forming  the  nuclei  of  nerves  are  analogous  to  those  of  the  cord, 
but  are  more  isolated.  They  also  give  exit  to  fibrils  which  unite 
them  to  other  cells  in  the  opposite  half  of  the  medulla  and  in  the 
brain  proper,  and  to  nerves  of  which  they  are  the  seat  of  origin.  In 
the  medulla  the  grouping  of  these  nuclei  is  quite  different  to  that 
found  in  the  spinal  cord.  However,  it  is  always  the  same  central 
gray  substance,  but  modified  in  its  form  and  arrangement.  The 
gray  matter  is  cut  here  and  there  by  white  columns  and  their  frag- 
ments. 

To  understand  this  new  disposition  of  the  gray  matter  it  is 
necessary  to  recall  that  at  the  level  of  the  medulla  the  central  gray 
substance  of  the  cord  has  been  pushed  backward  by  reason  of  sev- 
eral factors.  These  are:  the  separation  of  the  restiform  bodies,  the 
passage  outward  of  the  posterior  columns,  and  the  formation  of  the 
rhomboid  sinus.  The  latter  is  so  arranged  as  to  form  the  floor  of 
the  fourth  ventricle.  The  posterior  horns  have  become  separated 
and  are  so  rotated  upon  themselves  as  to  be  thrown  outward  and 
thus  placed  at  the  external  part  of  the  fourth  ventricle.  The 
anterior  cornua  have  their  bases  placed  upon  the  floor  of  the  fourth 
ventricle  on  each  side  of  the  median  raphe. 

The  isolated  horn  of  gray  matter  is  afterward  known  as  the 
nucleus  lateralis. 

Further,  the  crossed  pyramidal  tracts  of  fibers  are  carried  for- 
ward, outward,  and  upward.  By  the  oblique  passage  of  these  numer- 
ous white  fibers  through  the  gray  matter  of  the  anterior  horn  the 
anterior  horn  is  broken  up  so  that  the  caput  is  entirely  separated 
from  the  remainder  of  the  gray  matter.  The  fibers  in  passing 
through  the  base  of  the  anterior  horns  to  decussate  upon  the  median 
line  with  those  of  the  opposite  side  give  rise  to  the  reticulated  for- 
mation of  Deiters  and  to  the  raphe  of  Stilling. 

FoRMATio  Reticularis. — The  formatio  reticularis  is  an  asso- 
ciated system  of  the  short  fibers  with  nerve-cells  and  is  met  with 
at  any  point  between  the  spinal  cord  and  the  optic  thalamus.  These 
fibers  run  at  right  angles  to  one  another.  It  is  the  result  of  the 
decussation  of  the  crossed  pyramidal  and  arciform  fibers  which,  in 


558 


PHYSIOLOUY. 


their  march  forward  and  upward,  travel  through  the  base  of  the 
anterior  horns  in  the  form  of  a  multitude  of  small  bundles.  These 
arch  and  decussate  from  side  to  side. 

►Still  hiiihcr  up  the  fillet  decapitates,  as  it  were,  the  posterior 
horns.  The  caput  comes  close  to  the  surface,  where  it  forms  the 
distinct  projection  known  as  the  gelatinous  substance  of  Kolando. 
The  cervix  of  the  cornu  becomes  broken  uj)  in  a  manner  similar  to 
that  of  the  anterior  horn. 

White  Substance  of  the  Medulla. — This  is  formed  by  the  pro- 
longation of  tlie  columns  of  the  spinal  cord  and  l)y  additional  white 
masses,  the  olives  and  arcuate  fibers. 


NP 


Fiar.  244. 


Section  of  Medulla  Oblongata 
at  the  Level  of  the  Decussation  of 
the  Pyramids — Motor  Decussation. 
(M.  Duval.) 

1,  2,  3,  Anterior,  lateral  and  posterior 
columns.  CA,  RA,  Anterior  horns  and 
roots.  CP,  RP,  Posterior  horns  and 
roots.  RA,  Part  of  anterior  horn  whose 
head  CA  has  been  detached.  X,  De- 
cussation of  lateral  columns  at  pyra- 
mids (P,  P').  XP,  Nucleus  of  poste- 
rior pyramids,  a  and  p,  Anterior  and 
posterior  median  grooves. 


Section  of  Medulla  Oblongata 
at  the  Upper  Part — Sensory  or 
Fillet  Decussation.     (M.  Duval.) 

GA,  Head  of  anterior  horn.  CA, 
Base  of  anterior  horn,  nucleus  of 
hypoglossal  nerve.  H,  Root  fiber  of 
hypoglossal.  1,  2,  3,  Anterior,  lateral, 
and  posterior  columns,  a?,  x.  Fibers 
coming  from  the  posterior  columns 
and  forming  sensory  or  fillet  decussa- 
tion in  .v.  P,  P',  Pyramids.  NR,  Nu- 
cleus of  restiform  body.  NP,  Goll's 
nucleus.      CP,    Posterior   horn. 


White  Columns. — The  direct  ^pyramidal  tract,  whose  fibers 
decussate  the  length  of  the  cord  by  traversing  the  white  commissure, 
do  not  cross  at  the  level  of  the  medulla.  They  pass  directly  into 
this  organ,  to  be  placed  in  the  anterior  pyramid  of  the  correspond- 
ing side.  At  the  level  of  the  medulla  the  two  principal  anterior 
columns,  those  of  the  right  and  left,  which  heretofore  pursued  a 
parallel  course,  now   separate   from   the   median   line.     They  carry 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.  559 

themselves  outward  and  backward  for  a  little  distance,  then  bend 
inward  to  pursue  a  parallel  course  again.  By  this  course  there  is 
formed  a  sort  of  elliptical  buttonhole  which  is  inclined  obliquely  from 
bottom  to  top.  Traversing  this  buttonhole  are  found  the  crossed 
pyramidal  bundles;  both  are  carried  toward  the  median  line,  where 
they  decussate  with  the  opposite  side  to  produce  the  pyramidal  decus- 
sation. Thus,  the  two  principal  bundles  of  the  anterior  columns 
have  become  posterior  in  the  medulla,  where  they  are  placed  in  the 
deepest  part  of  the  pyramids. 

Lateral  Columns.  —  The  crossed  pyramidal  Ijundle  in  the 
medulla  bends  toward  the  median  line.  Here  it  meets  its  fellow 
of  the  opposite  side,  with  which  it  decussates  in  the  manner  of  a 
twist  to  arrive  in  the  opposite  side  of  the  medulla.  At  this  level,  in 
the  same  pyramid  of  the  medulla,  there  exist  side  by  side  the  direct 
pyramidal  column  of  the  same  side  of  the  cord  and  the  crossed  pyra- 
midal bundle  of  the  opposite  side.  These  two  bundles  now  form  one 
and  the  same  group  of  nerve-fibers.  This  type  of  fibers  forms  the 
pyramidal,  or  cerebral  motor,  tract.  Along  this  course  descend 
motor  messages  to  the  voluntary  muscles  from  the  brain  to  the 
anterior  horns  of  the  cord,  and  then  along  axis-cylinders  to  the 
motor  plates  in  muscles. 

An  act  incited  by  an  impulse  traveling  along  this  course  is 
always  crossed,  since  the  left  hemisphere  of  the  brain,  for  example, 
carries  the  order  of  motor  power  to  the  right  half  of  the  spinal  cord 
])y  the  crossed  pyramidal  fibers  and  to  the  left  half  of  the  spinal 
cord  by  the  direct  pyramidal  tract.  The  latter  tract  decussates 
throughout  the  length  of  the  cord  with  its  fellow  of  the  opposite 
side.  Thus,  the  result  is  that  the  decussation  is  total  for  the  pyra- 
midal tract  in  its  complete  action,  and  that  all  of  the  voluntary  parts 
excited  from  some  part  of  the  cerebral  hemisphere  end  in  muscles 
of  the  opposite  side  of  the  body.  From  this  the  student  will  deduce 
that  lesions  which  affect  the  pyramidal  tract  above  the  medulla 
oblongata  have  as  their  direct  result  a  motor  paralysis  opposite  to 
the  lesion ;    in  other  words,  a  crossed  hemiplegia. 

Posterior  Columns.  —  The  columns  of  Goll  ascend  to  the 
medulla,  where  they  pass,  without  decussation,  into  the  postpyra- 
midal  nucleus,  or  nucleus  of  Goll.  By  this  nucleus  it  is  carried  into 
the  cerebellum,  following  part  of  the  restiform  body;  another  part 
is  placed  in  relation  with  the  nuclei  of  the  pons. 

The  column  of  Burdach  comprises  the  longitudinal  commissural 
fibers,  the  root-fibers  of  the  posterior  roots,  and  the  sensory  fibers 


560  PHYSIOLOGY. 

issuing  from  the  column  of  Clarke.  The  root  and  commissural  fibers 
pass,  without  decussation,  into  the  cuneate  nucleus,  or  nucleus  of 
Burdach. 

Parts  added  to  the  medulla  oblongata,  which  are  not  found  in 
the  cord,  are:   arcuate  fibers  and  olives. 

Arcuate  fibers  are  the  curved  fibers  which  are  seen  in  transverse 
section  of  the  medulla.  By  reason  of  their  position  they  have  been 
termed  superficiat  and  deep,  or  external  and  internal. 

The  superficial  arcuate  fibers  form  a  more  or  less  voluminous 
ribbon.  They  are  fibers  which  come  from  the  cells  in  GolPs  and 
Burdach's  nuclei.  They  proceed  to  the  restiform  body  of  the  same 
side  and  thence  to  the  cerebellum. 

The  intei'nal  arcuate  fibers  likewise  proceed  from  the  cells  of  the 
nuclei  of  Goll  and  Burdach.  The  hindmost  fibers  form  the  sensory 
decussation  of  the  fillet.  Other  fibers  cross  the  median  raphe  in 
the  substance  of  the  medulla,  then  to  pass  upward  into  the  brain. 

The  olivary  body  is  formed  by  a  portion  of  the  white  cortical 
substance  which  belongs  to  the  lateral  column,  and  by  the  corpus 
dentatum,  a  layer  of  intervening  gray  matter  folded  upon  itself,  in 
such  a  manner  as  to  represent  an  oblong  purse.  This  is  open  at  its 
internal  aspect,  and  is  known  as  the  hilu^  of  the  olive.  The  corpus 
dentatum  of  the  olive  is  formed  by  a  great  quantity  of  small,  multi- 
polar cells.  The  fibers  which  emanate  from  it  go  to  the  olive  of  the 
opposite  side,  traversing  the  raphe  or  mounting  toward  the  pons. 

Pons  Varolii. 

The  pons  is  a  mass  of  nervous  tissue  placed  transversely  and  in 
the  form  of  a  half-ring.  It  is  situated  between  the  medulla  oblon- 
gata and  cerebral  peduncles,  which  limit  it  below  and  above,  respec- 
tively. The  cerebellar  hemispheres  bound  it  laterally.  Its  weight 
is  sixteen  or  seventeen  grams. 

For  examination  microscopically  the  pons  presents  six  surfaces 
or  faces. 

1.  The  anterior  face  is  free,  convex,  and  rounded,  and  rests  upon 
the  basilar  gutter  of  the  occipital  bone.  It  presents  an  antero-pos- 
terior  median  depression:  the  basilar  groove.  On  each  side  of  this 
are  two  parallel  prominences  due  to  the  heaving  up  of  the  annular 
fibers  by  reason  of  the  anterior  pyramids  which  pass  through  it. 

Upon  this  face  are  seen  the  transverse  fibers  which  pass  laterally 
to  penetrate  into  the  corresponding  hemisphere  of  the  cerebellum. 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM. 


561 


They  thus  form  a  large  column  upon  each  side,  known  as  the  middle 
cerebellar  peduncles. 

2.  The  posterior  face  forms  part  of  the  floor  of  the  fourth  ven- 


Fig.  245. — The  Base  of  the  Brain.  The  Left  Lobus  Temporalis  is 
in  Part  Represented  as  Transparent  in  Order  that  the  Entire  Course  of 
the  Optic  Tract  Might  be  Seen.      (Edinger.  ) 

tricle,  and  is  continuous  with  the  corresponding  face  of  the  medulla 
oblongata.  It  forms  a  triangle  whose  apex,  turned  upward,  is  placed 
at  the  level  of  the  lower  orifice  of  the  aqueduct  of  Sylvius.  The 
sides  of  this  triangle  are  formed  by  the  superior  cerebellar  peduncles. 

36 


562  IMIVSIOLOGY. 

Upon  the  median  line  it  has  a  groove  which  follows  that  of  the 
calamus  scriptorius.  Upon  each  side  there  exist  two  slight  depres- 
sions: the  one  known  as  the  super'wr  fovea,  the  other  the  locus 
ccoruleus. 

3.  A  superior  face. 

4.  The  inferior  face  is  continuous  with  the  base  of  the  medulla 
oblongata.  The  annular  fibers  of  the  pons  embrace  as  a  half-circle 
the  anterior  pyramids  of  the  medulla  oblongat^a. 

The  two  lateral  faces  (5  and  (J)  are  mingled  with  the  origin  of 
the  middle  cerebellar  peduncles.  The  peduncles  sink  into  the  hemi- 
spheres of  the  cerebellum,  where  they  are  lost. 

Structure  of  the  Pons. — The  pons  is  composed  of  nerve-fibers 
and  scattered  nerve-cells.  It  forms  a  kind  of  knot  into  which  con- 
verge the  fibers  coming  from  the  cerebellum,  as  well  as  those  passing 
to  and  fro  from  the  medulla  into  the  cerebral  peduncles. 

The  transverse  filjers  which  form  the  cortex  of  this  organ  go  in 
great  part  to  the  middle  cerebellar  peduncles.  They  are  the  com- 
missural fibers  which  unite  one  cerebellar  hemisphere  to  the  other. 

Some  fibers  emanate  from  the  middle  cerebral  peduncles  and 
decussate  on  the  median  line  with  those  of  the  opposite  side.  They 
thus  form  the  median  raphe.  They  terminate  in  the  gray  masses  of 
the  pons. 

Other  fibers,  having  decussated,  bend  upward  and  ascend  into 
the  cerebral  peduncles.  All  of  the  various  fibers — semi-annular, 
horizontal,  and  oblique — cover  in  the  longitudinal  fibers  which  unite 
the  medulla  oblongata  to  the  cerebral  peduncles.  In  them  various 
planes  are  formed:  (1)  there  is  a  superficial  plane,  or  stratum  zonale, 
which  covers  the  two  pyramidal  columns;  (2)  the  stratum  profundum, 
which  separates  the  pyramids  from  the  fillet  and  upper  part  of  the 
pons;  (3)  the  third  plane,  stratum  complexium-,  separates  the  cerebral 
tracts.  It  is  this  separation  which  gives  rise  to  the  formatio 
reticularis  of  the  pons  and  is  continuous  with  the  formatio  reticu- 
laris of  the  medulla. 

Between  the  superior,  or  pontal,  olives  there  is  a  system  of  fibers 
which  envelops  and  covers  the  olivary  nuclei  to  decussate  upon  the 
median  line  back  of  the  pyramids.  It  is  to  this  system  of  fibers 
which  unite  the  nuclei  of  the  auditory  nerves  and  the  olives  that 
Edinger  has  given  the  name  of  trapezoid  body. 

The  longitudinal  fibers  are  in  three  groups:  1.  The  anterior 
bundle,  which  contains  the  middle  fibers  of  the  cerebral  peduncle, 
and  is  continuous  with  the  superficial  motor  fibers  of  the  anterior 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM. 


563 


pyramids  of  the  medulla;  farther  down  it  is  still  in  connection  with 
the  pyramidal  tract  of  the  opposite  side  of  the  spinal  cord. 

2.  The  middle  column,  or  fillet. 

3.  The  third  group,  the  posterior  longitudinal  column,  passes 
along  the  floor  of  the  fourth  ventricle,  from  which  it  is  separated 
by  a  plane  of  transverse  fibers.  It  is  continuous  with  the  anterior 
column  of  the  cord  in  order  to  form  the  longitudinal  commissural 
column.     Some  of  the  fibers  of  this  bundle  decussate  with  their  fel- 

^. Anc.  Corp.  quad. 

Optic  tract. 


Sup.oliVie. 


Sup.  olive. 


Post,  longitudina]  bundle. 


P-'cn 


aii.A\ 


^::., 


Fig.  246. — Diagram  to  Illustrate  Some  of  the  Connections  of  the  Nuclei 
of  the  Nerves  to  the  Ocular  Muscles.     (Starling^  after  Held.) 

lows  of  the  opposite  side  to  unite  among  themselves  the  nuclei  of 
the  motor  nerves  of  the  eye  and  the  gray  mass  of  the  aqueduct  of 
Sylvius. 

Each  bundle  is  separated  from  its  fellow  by  a  plane  of  trans- 
verse fibers:    the  strata  zonale  and  profundum. 

The  gray  substance  of  the  pons  is  found  isolated  in  small  islands 
(nuclei  of  the  pons),  which  are  located  between  the  various  white 
layers  which  have  just  been  mentioned. 

One  of  these  nuclei,  the  most  voluminous  of  all,  is  situated  near 
the  median  raphe  at  the  site  of  the  junction  of  the  inferior  and 
middle  thirds  of  the  pons.     It  bears  the  name  of  reticulated  nucleus 


56-i 


PHYSIOLOGY. 


of  the  pons.  At  a  slightly  higher  level  is  found  another,  known  as 
the  central  nucleus.  To  these  two  nuclei  are  joined,  in  part,  the  root- 
bundles  of  the  antero-lateral  column  of  the  cord. 

In  addition,  as  a  continuation  of  the  posterior  horns  of  the  cord, 
there  exists  a  nucleus  which  gives  origin  to  the  trigeminus.  Inward 
and  somewhat  to  the  front  is  found  a  gray  mass  composed  of  large 
multipolar  cells.  These  represent  the  caput  of  the  anterior  horn. 
It  forms  the  nucleus  of  origin  of  the  motor  root  of  the  trigeminus. 

Upon  each  side  of  the  raphe  and  very  close  to  the  surface  of 
the  floor  of  the  fourth  ventricle  are  found  other  gray  nuclei,  as  of 
the  facial  and  abducent;    also  a  yellow  mass  of  an  S-shape  which 

12  y  4    5  6  7 


11  10     9       8 

Fig.    247. — Diagrammatic    Transverse    Section    Through    the    Crus 
Cerebri  and  Anterior  Corpora  Quadrigemina.     (Wali.ee,  after  Ober- 

STEIKER.) 

The  letters  a  m  p  on.  the  pes  or  crusta  signify  portions  occupied  by  fibers  from 
the  anterior,  middle  or  rolandic,  and  posterior  regions  of  the  cortex. 

1,  Pulvinar.  2,  Corpus  genie,  lat.  3,  Corpus  genie,  med.  4,  Corpora  quad. 
ant.  5,  Sylvian  aqueduct.  6,  Tegmentum.  7,  Crusta.  8,  Substantia  nigra.  9, 
Red  nucleus.     10,  Third  nerve.     11,  Optic  tract  (divided). 

forms  the  superior  olive  of  the  pons.  This  latter  is  connected  with 
the  auditory  apparatus.  The  gray  substance  of  the  medulla  is  pro- 
longed into  the  pons  to  form  the  origin  of  the  cranial  nerves. 

Cerebral  Peduncles. 

The  peduncles  of  the  brain  are  two  white  cords  which  extend 
from  the  superior  face  of  the  pons  in  a  divergent  manner  up  into  the 
optic  thalami.  They  are  somewhat  flattened  from  top  to  base.  Their 
volume  is  in  direct  relation  to  that  of  the  brain.  The  peduncles 
are  much  larger  than  the  columns  of  the  cord  reunited;    they  con- 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM. 


565 


tain  fibers  coming  from  the  gray  matter  of  tlie  medulla,  pons,  cor- 
pora quadrigemina,  locus  niger,  and  masses  of  gray  matter  lying  in 
a  line  along  the  aqueduct  of  Sylvius.  In  length  the  peduncles  meas- 
ure about  three-fourths  of  an  inch. 

Immediately  after  their  emergence  from  the  pons  they  separate, 
each  one  making  its  way  toward  its  corresponding  hemisphere  of  the 
cerebrum.  Between  them  there  remains  a  triangular  space,  the 
interpeduncular  space,  filled  in  its  back  part  by  a  cribriform  white 
layer  containing  a  great  number  of  vascular  openings.  The  latter 
is  known  as  the  posterior  perforated  space.     This  space,  bounded  in 


Fig.  248. — Section  of  the  Crus   Cerebri.      (Morat.) 

The  crusta  is  separated  from  the  tegmentum  by  the  locus  niger. 

1,  Aqueduct.  2,  Corpora  quad.  3,  Vent  gray  matter.  4,  Red  nucleus.  5, 
Locus  niger.  6,  Crusta.  7,  Furrow  for  the  oculo-motor  nerve.  8,  Sub.  perforat. 
posterior. 

front  by  the  optic  chiasm,  is  occupied  by  the  mammillary  eminences 
and  tuber  cinereum. 

Texture  of  the  Peduncles. — A  transverse  section  of  the  cerebral 
peduncles  gives  an  idea  of  the  architecture  of  the  large  nerve-trunks. 
In  a  cut  of  this  kind  it  is  seen  that  the  peduncles  are  separated  into 
two  white,  superposed  layers  by  a  black  line:   the  locus  niger. 

The  inferior  level,  or  crusta,  of  the  peduncle  is  formed  in  great 
part  by  a  large,  flat,  white  bundle  which  is  a  prolongation  of  the 
motor  fibers  extending  to  the  spinal  cord.  The  crusta  extends  from 
the  internal  capsule  through  the  pons  to  the  ventral  portion  of  the 
medulla  oblongata.  From  the  internal  capsule  its  fibers  become  lost 
in  the  cortical  layer  of  the  hemisphere  of  its  own  side. 

The  crusta  is  composed  of  two  bundles,  the  internal,  or  cortico- 


566  PHYSIOLOGY. 

pontal,  and  the  external,  or  voluntary  motor,  bundle.  The  cortico- 
pontal  bundle  acts  as  a  commissure  between  the  cerebrum  and  cere- 
bellum. It  passes  from  the  anterior  region  of  the  cerebrum  through 
the  peduncles  to  the  pons  and  medulla,  to  end  in  the  cerebellum. 
The  voluntary  motor  bundle  descends  from  the  motor  regions  of  the 
cortex  to  end  in  the  nuclei  of  origin  of  the  cranial  and  the  spinal 
nerves. 

Tegmentum. — The  superior  layer  of  the  cerebral  peduncle, 
known  as  the  tegmentum,  is  chiefly  the  formatio  reticularis  and 
fillet,  which  consists  of  masses  of  gray  matter  and  fibers  which  ex- 
tend through  the  posterior  end  of  the  medulla  oblongata,  pons,  and 
crura  up  to  the  optic  thalami.  At  the  height  of  the  corpora  quad- 
rigemina  is  a  reddish  column  formed  of  multipolar  cells.  It  is  the 
red  nucleus  of  the  tegmentum. 

The  Locus  Nigee,  which  separates  the  pes,  or  crusta,  from  the 
tegmentum,  consists  of  highly  pigmented  cells.  They  are  like  the 
cells  of  the  motor  regions  of  the  cortex.  Thus,  the  locus  niger  might 
be  considered  as  a  sort  of  motor  ganglion  whose  cells  are  charged 
with  black  j^igment. 

The  Fourth  Ventricle. 

The  fourth  ventricle  is  a  rhomboid  cavity  (sinus  rhomboidalis) 
imbedded  upon  the  posterior  surface  of  the  medulla  oblongata  and 
pons.  It  is  the  space  into  which  the  central  canal  of  the  cord  opens 
out  superiorly.  It  is  flattened  from  top  to  base;  and  has  an  inferior 
wall,  or  floor;   a  superior  wall,  or  vault;   and  four  angles. 

Floor  of  the  Ventricle. — The  floor  of  the  fourth  ventricle  is 
lozenge-shaped,  being  formed  by  two  triangles  placed  in  contiguity 
at  their  bases.  It  is  lined  by  a  layer  of  gray  matter,  which  is  but  a 
continuation  of  that  of  the  cord. 

The  inferior  triangle  (calamus  scriptorius)  belongs  to  the  pos- 
terior face  of  the  medulla;  the  superior  triangle  to  the  posterior 
face  of  the  pons. 

Upon  the  median  line  of  the  floor  there  is  a  slight  groove:  the 
handle  of  the  calamus.  On  each  side  of  this  groove  the  surface  of 
the  floor  presents  small,  rounded,  and  elongated  prominences.  These 
have  been  described  at  some  length  previously,  so  that  now  they  will 
be  but  mentioned.  In  the  inferior  triangle,  from  the  handle  of  the 
calamus  to  the  restiform  body,  they  are:  (1)  trigonum  hypoglossi; 
(2)  ala  cinerea,  or  trigonum  vagi;    (3)  trigonum  acustici. 

In  the  superior  triangle,  upon  each  side  of  the  median  groove 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.  567 

and  near  the  base  of  the  triangle,  are  seen  two  rounded  eminences: 
(1)  emineniia  teres  and  (2)  the  locus  coeruleus. 

The  various  eminences  correspond  to  the  origin  of  the  cranial 
nerves.  Thus,  in  the  locus  coeruleus  is  located  the  origin  of  the 
small  root  of  the  trigeminus;  in  the  teres  eminentia  the  common 
origin  of  the  facial  and  abducent;  in  the  trigonum  hypoglossi  is 
the  origin  of  the  hypoglossal  nerve;  in  the  ala  cinerea,  or  trigonum 
vagi,  occurs  the  origin  of  the  motor  roots  of  the  glosso-pharyngeal 
nerves,  pneumogastric,  and  spinal  accessory;  in  the  trigonum  acus- 
tici  are  found  the  fibers  of  the  auditory  and  the  sensory  fibers  of 
the  mixed  nerves,  glosso-pharyngeal,  vagus,  and  spinal  accessory. 
The  trigonum  hypoglossi  corresponds  to  the  funiculus  teres;  the  ala 
cinerea  to  a  depression:   posterior  fovea. 

At  the  level  of  the  middle  of  the  floor  of  the  fourth  ventricle 
a  variable  number  of  striae  go  out  from  the  median  groove  toward 
the  lateral  angles.  Here  they  converge  somewhat  and  form,  accord- 
ing to  some  authors,  the  posterior  root  of  the  auditory  nerve.  The 
striations  constitute  the  harhce  of  the  calamus. 

The  gray  matter  of  the  spinal  cord,  when  it  penetrates  into  the 
medulla,  exposes  itself  upon  the  floor  of  the  fourth  ventricle.  The 
horns  of  the  central  gray  column  of  the  cord  are  found  broken  up 
into  many  parts  by  the  decussation  of  the  pyramids  and  flllet.  By 
reason  of  this,  the  gray  matter  in  the  floor  of  the  ventricle  repre- 
sents four  irregular,  discontinuous  longitudinal  columns;  two  are 
central,  with  a  superflcial  one  on  each  side.  These  columns  are  pro- 
duced by  the  bases  and  detached  heads  of  the  anterior  and  posterior 
horns  of  the  central  gray  column.  From  the  anterior  gray  matter 
proceed  motor  nerves;  from  the  posterior  gray  matter  spring  sen- 
sory nerves. 

The  lateral  houndaries  of  the  ventricle  are,  in  the  lower  half, 
the  clavffi  of  the  funiculi  graciles,  the  cuneati,  and  the  restiform 
bodies.  In  its  upper  half  the  superior  peduncles  of  the  cerebellum 
form  the  limits. 

Aqueduct  of  Sylvius. 

The  aqueduct  of  Sylvius  is  a  canal  a  centimeter  and  a  half  long. 
It  is  hollowed  out  beneath  the  corpora  quadrigemina.  By  means  of 
this  aqueduct  the  fourth  ventricle  communicates  with  the  third.  It 
is  derived  from  the  middle  cerebral  vesicle.  Its  walls  are  formed 
above  by  the  valve  of  Vieussens,  the  corpora  quadrigemina,  and  the 
white,  posterior  commissure.     Its  base,  or  floor,  is  formed  by  the 


568 


PHYSIOLOGY. 


tegmentum.  Its  floor  is  grooved  by  the  continuation  of  the  median 
groove  of  the  fourtli  ventricle.  Its  walls  are  composed  of  gray  mat- 
ter continued  from  the  spinal  cord. 


Fillets. 


The  chief  fillet  consists  of  the  axis-cylinders  from  Goll's  and 
Burdach's  nuclei,  which  decussate  under  the  floor  of  the  fourth  ven- 


iBurdacb 


Fig.  249. — The  Mesial  Fillet,  Ending  Chiefly  in  the  Ventral  Nucleus 
of  the  Optic  Thalamus  and  then  United  by  Xew  Neuraxons  (Upper 
Fillet)   to  Parietal  Cortex. 


tricle,  then  pass  up  through  the  tegmentum,  and  chiefly  end  in  the 
ventral  nucleus  of  the  optic  thalamus.  From  new  neuraxons  it  goes 
through  the  posterior  part  of  the  internal  capsule  to  the  ascending 
parietal  convolutions.     It  is  a  continuation  of  the  sensory  tract. 

The  lateral  fillet  also  starts  from  the  nuclei  of  Goll  and  Burdach 
and  is  chiefly  composed  of  axis  cylinders  from  the  end  nuclei  of  the 
auditory  nuclei  and  the  superior  olivary  body;    it  then  passes  into 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.  569 


Fig.  250. — View  from  the  Side  and  Slightly  from  Above  and  Behind 
of   the    Right    Hemisphere    of    a    Simply    Convoluted    European    Brain. 

(QUAIX.) 

Sulci— J?o.,  Rolandic  or  central,     o.  Its  superior  genu.     Sij.  n.   Anterior  limb 
of  Sylvian   (x,   ascending   part;     ?/,   horizontal   part).     8y.   p,    Posterior  limb  of 


570  PHY8T0L0nY. 

the  posterior  corpora  quadrigcinina,  and  thence  by  means  of  the 
brachium  posterioris  of  the  corpora  quadrigemina  through  the  pos- 
terior limb  of  the  internal  capsule  to  the  first  and  second  temporal 
convolutions.     It  is  made  up  mainly  of  auditory  fibers. 

THE  BRAIN. 

The  weight  of  the  brain  is  about  fifty  ounces.  However,  the 
weight  of  the  brain  may  be,  as  in  the  case  of  Cuvier,  sixty-five 
ounces.  It  is  greater  in  civilized  persons  than  in  savage  tribes;  it 
is  likewise  greater  in  the  male  than  in  the  female;  in  an  eminent 
man  than  in  an  ordinary  man.  But  what  really  shows  the  superiority 
of  the  brain  is  not  so  much  its  enormous  size  nor  the  exuberance  of 
its  convolutions,  but  the  well-balanced  development,  the  harmony, 
of  all  of  its  parts. 

External  Form.— The  brain  is  composed  of  two  symmetrical 
halves,  or  hemispheres.  These  are  nearly  entirely  separated  from  one 
another  by  the  great  longitu-dinal  fissure.  The  parts  which  are  intact 
are  located  at  the  center  and  base  and  comprise  the  corpus  callosum 
and  floor  of  the  fourth  ventricle.  The  surfaces  of  the  hemispheres 
are  separated  into  lobes  and  convolutions  by  various  fissures.  The 
convolutions  appear  to  be  infoldings  of  the  gray  matter  of  the  brain 
within  its  rigid  confines,  the  cranial  vault.  The  mode  of  spreading 
of  the  fibers  of  the  peduncle  may  have  something  to  do  with  their 
conformation  also.  The  end  obtained  by  their  presence  is  to  lodge 
a  much  larger  gray  mass  within  a  given  space. 

There  are  five  principal  fissures  in  the  brain :  (1)  the  great  longi- 
tudinal;   (2)  the  great  transverse  fissure  between  the  cerebrum  and 


Sylvian.  8y.  p.  asc.  Ascending  ramus  of  posterior  limb,  fi,  Superior  frontal. 
^2.  Inferior  frontal.  f:<„  Middle  frontal,  ft.  Paramesial  frontal.  (/,  Diagonal, 
placed  in  this  instance  rather  low  down,  and  communicating  with  the  Sylvian. 
p.c.  inf,  Inferior  precentral.  p.c.i.  ant.,  Its  anterior  ramus,  p.c.  sup.,  Superior 
precentral.  p. cm,  Mesial  precentral.  p.c.  ir..  Transverse  precentral.  rtc.  tr.. 
Transverse  retro-central,  i.-p.  inf,  Intra-parietal,  pars  inferior  (inferior  post- 
central), i.-p.  Slip.,  intraparietal,  pars  superior  (superior  postcentral),  i.-p. 
post.  s.  hor.,  Intraparietal,  pars  posterior  seu  horizontalis.  i.p.  post.,  Intra- 
parietal, pars  posterior  (parocaipital  of  Wilder),  i.-p.  pr.  asc.  An  ascending 
branch  of  the  intraparietal.  p.-o.,  Parieto-occipital.  occ.  ant..  Anterior  occipital. 
ocr.  lat..  Lateral  occipital,  mic.  Posterior  end  of  calcarine.  t-i.  First  temporal 
or  parallel.  <i  asc.  Its  posterior  ascending  extremity,  detached.  <2,  Second  tem- 
poral, fo  asc.  Its  posterior  ascending  extremity  joined  to  and  apparently  con- 
tinuous with  the  first  temporal. 

Gyri— Fi,  Fn,  F3,  First,  second,  and  third  (superior,  middle,  and  inferior) 
frontal,  a.  Posterior  part  of  third  frontal.  6,  Middle  part  (pars  triangularis). 
c.  Orbital  part.  AF.,  Ascending  frontal.  A. P.,  Ascending  parietal.  Ti,  T2,  Tg, 
First,  second,  and  third  temporal. 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.  571 

cerebellum;  (3)  the  fissu)-e  of  Sylrius;  (4)  fissure  of  Rolando;  (5) 
parieto-occipital  fissure. 

As  previously  stated,  the  great  longitudinal  fissure  runs  antero- 
posteriorly  to  separate  the  two  hemispheres  of  the  brain. 

At  its  posterior  end  and  at  right  angles  to  it  lies  the  great 
transverse  fissure.  By  it  the  posterior  portion  of  the  cerebrum  is 
separated  from  the  cerebellum. 

The  fissure  of  Sylvius  begins  at  the  base  of  the  brain  at  the 
anterior  perforated  space.     It  passes  outward  to  the  external  sur- 


Fig.  251. — Lateral  Aspect  of  Brain.      (Edinger.) 

The  gyrus  centralis  anterior  is  the  ascending  frontal  convolution.  The  gyrus 
centralis  posterior  is  the  ascending  parietal  convolution.  Sulcus  centralis,  fissure 
of  Rolando. 

face  of  the  hemispheres,  where  it  divides  into  two  branches.  The 
one  branch  passes  upward  (ascending  limb) ;  the  other,  a  larger  one, 
runs  nearly  horizontally  backward  (horizontal  limb). 

The  fissure  of  Rolando  commences  at  the  great  longitudinal 
fissure,  half  an  inch  behind  its  middle  point,  measuring  from  the 
glabella  to  the  external  occipital  protuberance.  It  runs  downward 
and  forward  to  terminate  a  little  above  the  horizontal  limb  of  the 
fissure  of  Sylvius. 

The  parieto-occipital  fissure  commences  about  midway  between 
the  posterior  extremity  of  the  brain  and  the  fissure  of  Eolando  and 
runs  downward  and  forward  for  a  variable  distance. 


572 


PHYSIOLOGY. 


Fig.  252. — Mesial  Aspect  of  Left  Hemisphere  of  a  European 
Brain.      (QuAiN.) 

Sulci — Ro.,    Upper    end    of    Rolandic.     p. cm..    Mesial    precentral.      f^,    Mesial 
frontal,     cm.,  Calloso-marginal.     ;»•.   1.,  Prelimbic  (anterior  end  of  calloso-mar- 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM. 


573 


The  fissures  which  have  just  been  mentioned  are  made  use  of 
to  map  out  the  surface  of  the  hemispheres  into  regions  to  which  the 
term  lobes  has  been  ajjplied.  This  mapping  is  purely  artificial  and 
has  no  clinical  or  pathological  bearing;  in  many  instances  the  lines 
dividing  the  lobes  are  purely  imaginary.  However,  anatomists  are 
accustomed  to  speak  of  six  lobes:  (1)  frontal;  (2)  parietal;  (3) 
occipital;    (-t)  temporal :    (5)  limbic,  and  ((5)  island  of  Reil. 


Fig.  253. — Longitudinal  Section  Through  the  Middle  of  an  Adult 
Brain.  The  posterior  portion  of  the  thlamus,  the  crura  cerebri,  etc., 
have  been  removed,  in  order  to  expose  the  inner  surface  of  the  temporal 
lobe.      (Edixger.  ) 

The  island  of  Beil,  or  central  lobe,  is  located  at  the  bottom  of 
the  fissure  of  Sylvius.  It  is  a  portion  of  the  cerebral  cortex  which 
is  overhung  by  the  operculum. 

The  convolution  of  Broca  is  that  portion  of  the  inferior  frontal 


ginal).  pr.  I.  asc,  An  ascending  branch  of  the  prelimbic.  parncentr..  Paracen- 
tral (posterior  end  of  calloso-marginal).  p.l.,  Post-llmbic.  ro.  Rostral,  ro.  inf.. 
Inferior  rostral,  p.-o.,  parieto-occipital.  calc.  ant..  Stem  of  calcarine.  calc. 
post..  Posterior  part  of  calcarine.  1,  2,  3,  4,  Places  where  annectent  gyri  occur 
in  calcarine  and  parieto-occipital  fissures,  ts,  Third  temporal,  coll.,  collateral 
or  fourth  temporal.  7(  (placed  on  the  fascia  dentata)  has  the  hippocampal  fissure 
just  below  it. 

Gyri — Fi,  Marginal  part  of  first  frontal.  C,  callosal  (gyrus  fornicatus).  U, 
Hippocampal.  unc.  Its  uncus.  7(,  Dentate.  7*4,  Fourth  temporal  (fusiform 
lobule).     To,   Fifth  temporal   or  infracalcarine  (lingual  lobule). 

cc.  Corpus  Callosum.  upl.,  Its  splenium.  g.  Its  genu,  r.  Its  Rostrum,  fo. 
Fornix,    fi..  Fimbria. 


Fig.  254. — Section  Through  the  Cerebral  Cortex  of  a  Mammal. 
(Edinger  and  Cajal.) 
1,    Superficial,   or  molecular,   layer.     2,   Layer  of   small   pyramidal   cells.     3, 
Layer  of  large  pyramidal  cells.     4,  Layer  of  polymorphous  cells,     a,   b,  c.   Gan- 
glionic cells,     d.  Fusiform  cells,     e.   Fibers,     f,  Pyramidal  cells,     g.  Multipolar 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM. 


575 


convolution  which  winds  around  the  ends  of  the  anterior  and  ascend- 
ing limbs  of  the  fissure  of  Sylvius.  It  is  characteristic  in  that  it  is 
the  speech-center  and  also  that  it  is  better  developed  upon  the  left 
side  in  right-handed  people. 


VentriculuS 

tertius. 


Zwisclienhirrt 


MiUeUiirn. 


Hirderhtrn  zl/'i' 


J^achJnm.  /\f^' 


Hurken-mark . 


tnaearm . 


Keissnba^ 


Fig.  255. — The  Brain-structures  from  the  Thahimus  to  the  Spinal  Cord 
(the  "Brain-stem").      (Edixger. ) 

The  cerebellum  divided,  and  removed  on  the  left.  Bindenrm,  Peduncle. 
Hinterhirn,  Hindbrain.  Hinisrhenkel,  Crus  Cerebri.  Kleiiihirn,  Cerebellum. 
Mittelhirn,  Midbrain.  Xachhini,  After-brain.  Rikkeninark,  Spinal  Cord. 
Zicisclicnhirn,  Interbrain. 

On  the  internal,  or  mesial,  aspect  of  the  hemispheres  are  the 
following  fissures  and  convolutions:  The  convolution  immediately 
bounding  the  corpus  callosum  is  termed  the  gyms  fornicatus;    the 


576 


PHYSIOLOGY. 


hij)])oe;impal  gyrus  ends  inferiorly  in  a  crochetlikc  extremity,  termed 
the  uncus.  The  gyri  f ornicatus  and  hippocampus  together  form  the 
great  limbic  lobe;  the  marginal  convolution  is  merely  the  internal 
aspect  of  the  convolutions  of  the  frontal  and  parietal  lobes.  That 
portion  which  forms  the  mesial  aspect  of  the  ascending  frontal  con- 


Fig.  250. — Thalamus  and  Corpora  Quadrigemina  Seen  from  the  Side. 

(Edinger.  ) 

The  forebrain  removed  at  the  point  where  its  coronal  fibers  pass  into  the 
capsula  interna.  The  relations  of  the  optic  radiation  to  the  posterior  part  of  the 
capsula  interna  and  to  the  point  of  origin  of  the  opticus  are  shown  diagram- 
matically.  Bindeurm,  Peduncle.  Fuss,  Pes,  or  crusta.  Uint.  Arm.,  Posterior 
brachium.  Stabkrans  zn  den  Optic  Centr.,  Coronal  fibers  to  the  optic  centers. 
V.  Arm.,  Anterior  brachium. 

volution  is  known  as  the  paracentral  lobule.  Upon  the  mesial  aspect 
of  the  postero-parietal  lobule  is  a  quadrilateral  lobule :  the  praecuneus. 

Between  the  parieto-occipital  and  calcarine  fissures  is  a  wedge- 
shaped  lobule  called  the  cuneus. 

Structure  of  the  Cerebral  Convolutions. — The  gray  matter  of  the 
cerebral  cortex  has  been  divided  into  four  layers: — 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM. 


577 


1.  The  superficial  layer. 

2.  The  layer  of  small  pyramidal  cells. 

3.  The  layer  of  large  pyramidal  cells. 

4.  The  layer  of  polymorphous  cells. 

The  first  layer  contains  the  cells  of  Cajal.  In  this  layer  termi- 
nate many  of  the  fibers  coming  from  the  spinal  cord,  medulla,  and 
cerebellum. 


_    Cenfral 


V^-^A 


Fig.  257. — Median  Sagittal  Section  Through  the  Interbrain  and  the 
Structures  Posterior  to  it.      (Edinger.  ) 

The  course  of  a  number  of  coronal  fibers  is  indicated  by  lines:  Zur  liriirke. 
To  the  pons.  PyramUlen  Fasern,  Pyramidal  fibers.  Hnuhenstrahlung,  Tegmental 
radiation.  Zu  den  Optirusccntrcn,  To  the  opticus  centers.  Haube,  Tegmentum. 
PyramMenkrcuzung,  Pyramidal  decussation. 


The  second  layer  contains  the  small  pyramidal  cells,  whose 
axons  run  into  the  superficial  layer. 

The  third  layer  contains  the  cells  of  Martinotti,  witli  tlie  large 
pyramidal  cells. 

The  fourth  layer  is  made  up  of  triangular,  small  pyramidal,  and 
spindle  cells. 

37 


578  PHYSIOLOGY. 

'The  ivhite  matter  of  llie  hemispheres  consists  of  medullated 
fihors  whose  size  is  very  various.  As  a  rule,  however,  they  are 
smaller  than  those  of  the  cord  and  bulb.  For  the  most  part,  they 
are  arranged  in  bundles  sei)arat('d  l)y  layers  of  neuroglia. 

Central  Ganglia  of  the  Brain. — At  the  level  of  the  hilus  of  the 
brain  the  cerebral  peduncles  sink  into  the  body  of  the  two  hemi- 
spheres. They  contain  fibers  which  proceed  from  the  cord,  pons, 
and  cerebellum  to  the  brain,  as  well  as  those  fibers  which  proceed 
fi'om  the  brain  to  the  cord,  pons,  and  cerebellum.  There  are  also 
direct  fibers  which  reach  from  the  peduncles  to  the  Ijrain  cortex. 
However,  there  are  other  indirect  or  ganglionic  fibers  which  com- 
municate previouvsly  in  the  nuclei  or  ganglia  of  the  gray  substance. 
The  ganglia  referred  to  are :  the  optic  thalami  and  the  corpora  striata. 
The  optic  thalami  are  two  oval  bodies  placed  upon  the  tract  of  the 
cerebral  peduncles.  At  the  posterior  part  of  the  thalamus  are  the 
external  and  internal  geniculate  bodies.  Between  the  pulvinar  and 
the  origin  of  the  pineal  gland  is  found  a  small  surface,  slightly 
depressed  and  of  triangular  form ;  it  is  the  triangle  of  the  habenula. 
Within  this  triangle  is  a  small  prominence  known  as  the  nucleus  of 
the  habenula.     The  habenula  is  the  peduncle  of  the  pineal  gland. 

The  inferior  surface  of  the  thalamus  rests  upon  the  cerebral 
peduncle,  from  which  it  receives  some  fibers.  In  the  rear  it  remains 
free,  and  presents  two  nipplelike  swellings:  the  geniculate  bodies. 
One  lies  internal;   the  other  external. 

JMonakow  divides  the  nuclei  of  the  thalamus  as  follows:  (1) 
anterior,  (2)  median,  (3)  ventral,  (4)  posterior,  and  (5)  pulvinar. 
The  posterior  root-fibers  arborize  about  the  nuclei  of  GoU  and  Bur- 
dach.  From  there  they  are  continued  by  a  second  neuraxon  to  end 
in  the  ventral  nucleus  of  the  thalamus. 

Each  thalamus  has  a  double  connection  with  all  parts  of  the 
cerebral  cortex  by  neuraxons  from  its  various  nuclei  to  the  cortex, 
and  by  neuraxons  from  the  pyramidal  cells  of  all  parts  of  the  cortex. 
The  neuraxons  of  the  ganglionic  cell-layer  of  the  retina  end  about 
the  cells  of  the  pulvinar  and  external  geniculate  body,  thus  connect- 
ing it  with  the  primary  division  of  the  optic  tract.  It  has  also  a 
dou1)le  connection  with  the  occipital  lobes  by  neuraxons  from  the 
pulvinar  cells  (optic  radiations),  which  terminate  in  the  pyramidal 
cells  of  the  occipital  cortex  and  by  neuraxons  from  the  pyramidal 
cells  of  that  lobe  which  end  in  the  cells  of  the  pulvinar. 

Corpora  Striata. — The  corpora  exist  as  two  large  ovoid  gray 
masses  lodged  within  the  thickness  of  the  frontal  lobe.     They  are 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEIM. 


579 


situated  in  front  of  and  slightly  outward  from  the  optic  thalami. 
The  outer  surfaces  of  the  corpora  are  in  relation  with  the  island  of 
Reil  and  the  centrum  ovale  of  the  hemispheres.  Internally,  they 
are  in  apposition  with  the  optic  thalami  and  the  gray  layer  of  the 
third  ventricle.  They  are  formed  of  two  large  nuclei :  the  caudate 
and  lenticular. 

The  nucleus  caudatus  is  so  named  from  its  resemblance  to  a  pear 
in  shape.     It  lies  inside  the  lateral  ventricle  upon  its  floor.     The 


for.Mon. 


fornix 


trangv.figg, 

pineal  glrxa 
post.  comm. 
lineal  hody 


in/umlil) 

pit.  hodij 

Corp.  alb. 


tuh.valv. 
■pxjramii. 
Fig.  2.58. — Median  Section  of  the  Brain.      (Quain.) 

cells  of  this  nucleus  are  of  two  types — sensory  and  motor;  the  cells 
of  the  motor  type  seem  to  be  more  abundant. 

The  nucleus  lenticularis,  a  part  of  the  corpus  striatum,  is  sepa- 
rated from  the  caudate  nucleus  by  the  internal  capsule.  By  reason 
of  its  situation  near  the  center  of  the  body  of  the  hemisphere  and 
outside  of  the  ventricle  it  is  called  the  extraventricular  nucleus  of 
the  corpus  striatum. 

The  lenticular  nucleus  is  divided  into  three  segments  by  two 
layers  of  white  matter  placed  within  its  thickness.  The  segments 
are  distinguished  from  one  another  by  their  color,  which  is  most 
pronounced  in  the  external  segment.     The  latter  has  received  the 


580 


PHYSIOLOGY. 


name  of  putamen.     The  two  other  segments  are  known  as  the  in- 
ternal and  external  segments  of  the  globus  pallidus. 

Hence  it  ensues  that  the  corpus  striatum  has  the  general  char- 
acter of  the  letter  e.  Its  upper  extremity,  or  branch,  being  repre- 
sented by  the  caudate  nucleus;    its  lower  branch  by  the  lenticular 


Fig.  259. — So-called  Ganglionic  Gray  Matter  of  the  Cerebral  Trunk. 
(After  Chaepy. )  Gray  Masses  Superadded  to  the  Sensori-niotor  Nuclei. 
( MORAT. ) 

1,  Pontal  nucleus.  2,  Arriform  nucleus.  3,  Olive.  4,  Speech.  5,  Reticulat. 
formation.  6,  Trapezoid  nucleus.  7,  Superior  olive.  8,  Substant.  cin.  9,  Lateral 
nucleus.  10,  Locus  coeruleus.  11,  Locus  niger.  12,  Red  nucleus.  13,  Corpora 
quadrigemina. 


nucleus.  The  point  of  union  of  the  two  forms  the  knee.  The  cor- 
pora striata  are  of  cortical  origin,  and  not  of  central  origin,  as  is 
the  thalamus.  That  is  to  say,  the  nerve-impulses  of  voluntary  move- 
ment ordered  by  the  cortex  descend  to  the  corpora  striata,  where 
they  undergo  transformation  before  appearing  as  muscular  move- 
ments. 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM. 


581 


The  Claustrum. — To  the  corpora  striata  is  attached  a  thin  layer 
of  gray  substance,  so  placed  that  it  occupies  the  field  between  the 
lenticular  nucleus  and  the  island  of  Eeil.  This  band,  derived  from 
the  cortex  in  a  manner  similar  to  those  fibers  of  the  corpora  striata 
just  mentioned,  is  the  claustrum.     It  is  separated  from  the  external 


Fig.  260. — Ideal  Horizontal  Section  Through  the  Riglit  Hemisphere  and 
Basal  Ganglia.     (Waller,  after  Charcot.) 

To  illustrate  the  position  of  the  internal  capsule  taken  in  transverse  section; 
HAL  indicate  the  situations  in  the  internal  capsule  of  fibers  governing  the 
movements  of  the  head,  arm,  and  leg  respectively. 

1,  Caudate  nucleus.    2,  Frontal.     3,  Genu.    4,  Temporo-occipital.    5,  Optic 
thalamus.    6,  Hippocampus.    7,  Lenticular  nucleus. 

surface  of  the  lenticular  nucleus  by  a  band  of  white  substance :    the 
external  capsule. 

The  claustrum  is  composed  of  spindle  cells,  quite  like  those 
found  in  the  deep  layer  of  the  cortex.  The  claustrum  should  be  con- 
sidered as  a  part  of  the  cortex  that  has  been  detached  by  reason  of 
the  passage  of  a  bundle  of  fibers  of  association.  These  fibers  unite 
the  various  convolutions  among  themselves. 


582 


PHYSIOLOGY. 


The  corpora  quadrigemina  are  four  small  bodies  or  rounded 
eminences.  They  are  composed,  for  the  great  part,  of  gray  matter, 
although  covered  externally  by  and  containing  in  their  interior  some 
white  fibers.     They  lie  beneath  the  pulvinar  of  the  optic  thalamus. 

The  corpora  are  arranged  in  two  pairs:  one  anterior,  the  other 
posterior. 

The  upper,  or  anterior,  pair  is  broader,  longer,  and  darker  than 
the  posterior  pair.  Laterally  the  corpora  extend  into  distinct  and 
prominent  tracts  of  white  substance. 

The  loiver,  or  posterior,  corpora  are  composed  almost  entirely  of 
gray  matter. 

Internal  Capsule. — The  name  of  internal  capsule  is  given  to  a 
thick  band  of  white  fibers  situated  between  the  optic  thalamus  and 
caudate  nucleus  on  one  side  and  the  lenticular  nucleus  on  the  other. 
In  a  frontal  section  of  the  brain  the  tract  is  seen  to  follow  a  course 


Fig.  2G1. — Internal   Capsule.      (Sherrington.) 


upward  and  outward  in  an  oblique  manner  between  the  preceding 
nuclei.     Downward  it  is  continuous  with  the  cerebral  peduncle. 

Where  the  capsule  enters  the  lenticulo-striate  defile  it  expands 
like  a  bundle  of  stalks  to  form  the  corona  radiata  of  Eeil. 

If  studied  horizontally,  the  internal  capsule  is  seen  to  present 
the  shape  of  an  angle  opening  outward  and  embracing  the  lenticular 
nucleus.  The  capsule  seems  to  be  composed  of  two  parts  or  segments 
and  a  tend,  or  genu. 

The  anterior  -segment  is  placed  between  the  lenticular  and 
caudate  nuclei ;  it  bears  the  name  of  arm,  or  lenticulo-striate  segment. 
The  posterior  segment,  situated  between  the  optic  thalamus  anfl 
lenticular  nucleus,  for  this  reason  takes  the  name  of  lenticulo-optic 
segment. 

The  point  of  union  of  the  two  segments  is  called  the  Icnee,  or 
genu.  Its  position  is  exactly  at  the  center  of  the  three  nuclei  just 
mentioned. 

Capsular  Structure. — With  the  naked  eye  or  even  a  micro- 
scope the  internal  capsule  presents  itself  as  a  homogeneous  structure, 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.  5S3 


A.U^J' 


Fig.  262.— Motor  Tract.      (Morat.) 


1,   Pyramidal   cell.     2,   Geniculate  tract.     3,   Motor  decussation.     4,   Tiirck   tract. 
5,  Cells  of  anterior  horn.    6,  Muscle  fiber.    7,  Crossed  pyramidal  tract. 


584  PHYSIOLOGY- 

composed  of  white  fibers.  There  is  nothing  in  its  appearance  to  let 
anyone  suppose  that  there  are  different  tracts  or  bundles.  However, 
pathological  anatomy,  with  its  secondary  degeneration,  and  embry- 
ology, by  reason  of  the  myelin  appearing  in  the  bundles  at  different 
stages  of  development  of  the  foetus,  reveal  a  number  of  segments  per- 
fectly separated  either  from  a  functional  or  pathological  point  of 
view. 

The  three  bundles  of  fibers  are  distributed  somewhat  as  follows 
in  the  capsule: — 

1.  The  Cortico-Pontal-Cerebellar  Tract  is  composed  of  neuraxons 
from  the  pyramidal  cells  of  the  frontal  lobes.  Then  the  neuraxons 
pass  through  the  anterior  two-thirds  of  the  anterior  segment  of  the 
internal  capsule,  then  through  the  crusta,  ending  in  some  of  the 
pontal  nuclei.  These  pontal  nuclei  are  joined  by  neuraxons  to  the 
fibers  chiefly  from  half  of  the  cerebellum  of  the  opposite  side  by 
the  middle  cerel)ellar  peduncles,  although  some  fibers  are  from  the 
cerebellar  half  of  the  same  side.  Hence  the  frontal  lobes  are  ana- 
tomically connected  with  the  opposite  cerebellar  hemisphere. 

2.  The  Motor  Tract  arises  from  the  neuraxons  of  the  large  pyra- 
midal cells  of  the  ascending  frontal  convolutions;  then  goes  through 
the  anterior  two-thirds  of  the  posterior  segment  of  the  internal 
capsule;  then  through  the  crusta  to  the  anterior  pyramids  of  the 
medulla  oblongata,  where  they  partly  decussate,  becoming  the  crossed 
pyramidal  tract  of  the  opposite  side  of  the  spinal  cord,  and  ending  in 
the  cells  of  the  anterior  horns.  Part  of  the  motor  tract  passes  down 
on  the  side  upon  which  it  originated  as  the  tract  of  Tiirck,  then 
through  the  anterior  white  commissure  into  the  cells  of  the  anterior 
horn  of  the  opposite  side  of  the  cord.  Here  we  have  a  long  neuraxon 
or  axon  from  the  motor  convolution  to  tlie  anterior  horns  of  the 
opposite  side  of  the  spinal  cord.  From  here  a  second  axon  starts  out 
to  supply  the  muscles,  making  only  two  axons  in  the  motor  tract. 

The  motor  tract  includes  a  band  of  fibers  running  from  the 
cortex  to  the  nucleus  of  the  various  motor  cranial  nerves.  Thus 
the  cortex  sends  motor  fibers  to  the  nucleus  of  the  third,  the  fourth, 
the  motor  division  of  the  fifth,  the  sixth,  the  seventh,  the  motor 
divisions  of  the  ninth  and  tenth,  and  the  eleventh  and  twelfth  pairs. 
We  only  know  the  cortical  origin  of  the  seventh,  the  motor  branch  of 
the  fifth,  and  the  hypoglossal,  and  these  originate  from  the  lowest 
third  of  the  ascending  frontal  convolution;  then  they  pass  through 
the  knee,  or  genu,  of  the  internal  capsule  and  continue  through  the 
crusta  until  they  end  in  the  nuclei  of  the  various  cranial  motor  nerves. 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTE^M.  585 


Fig.   263.— Sensory   Tract.      (Morat.) 

1  Fillet  2  Cranial  sensory  nerve.  3,  Sensory  decussation.  4,  Nucleus  of 
Goll'and  of  Burdach.  5,  Column  of  Goll.  6.  Anterior  column.  7.  Lateral  col- 
umn     8    Anterior  commissure.     9.  Posterior  cornu.     10.  Spinal  nerve. 


586  ..  PHYSIOLOGY. 

As  this  tract  passes  through  the  genu  of  the  capsule  it  is  known  as 
the  geniculate  tract:    a  })art  oT  the  main  motor  tract. 

3.  The  Sensory  Trad. — Its  axons  arise  in  the  ganglion  of  the 
posterior  root  and  extend  from  the  skin  and  muscles  to  the  spinal 
cord,  where  they  divide  into  an  ascending  and  descending  branch. 
The  descending  branches  arborize  about  the  cells  in  the  gray  matter 
of  the  cord.  The  ascending  branches  in  great  part  ascend  in  the 
columns  of  Goll  and  Burdach  and  arborize  in  the  cells  of  the  nuclei 
of  Goll  and  Burdach.  From  the  nuclei  of  Goll  and  Burdach  a  sec- 
ond series  of  axons  pass  under  the  name  of  the  fillet  or  lemniscus  or 
interolivary  tract,  decussating  under  the  floor  of  the  fourth  ventricle 
and  chiefly  arborize  about  the  cells  of  the  ventral  nucleus  of  the 
thalamus.  From  the  ventral  nucleus  a  third  set  of  neuraxons  arise 
and  go  through  the  posterior  part  of  the  posterior  segment  of  the 
internal  capsule  to  the  ascending  parietal  convolution.  This  tract 
receives  also  the  neuraxons  of  the  sensory  nuclei  of  the  cranial 
nerves  running  to  the  cortex,  excepting  the  auditory  nucleus. 
In  the  internal  capsule  the  motor  fibers  going  to  the  face  are 
in  front;  next  the  arm-  and  then  the  leg-  fibers.  Hence  lesions 
occurring  in  the  anterior  two-thirds  of  the  posterior  limb  of 
the  capsule  cause  motor  troubles ;  lesions  in  the  posterior  third  cause 
sensory  troubles.  The  sensory  tract  is  composed  of  three  neurax- 
ons: one  from  the  skin  to  Goll's  and  Burdach's  nuclei,  the  second 
from  these  nuclei  to  the  ventral  nucleus  of  the  thalamus,  and  the 
third  from  this  ventral  nucleus  to  the  cortex.  Pain  and  temperature 
sensations  travel  through  the  gray  matter.  Some  sensory  impulses 
can  travel  by  way  of  the  cerebellum  to  the  cerebrum. 

Blood-supply  of  the  Brain. — The  brain  is  freely  supplied  with 
arteries.  The  brain  with  its  enveloping  membrane  is  said  to  receive 
fully  one-fifth  of  the  entire  quantity  of  blood  within  the  body. 

The  brain  with  its  adnexa  is  supplied  by  the  hvo  vertebraU  and 
the  two  internal  carotids,  with  their  numerous  branches.  These 
principal  vessels  form  a  free  anastomosis  at  the  base  of  the  brain, 
known  as  the  circle  of  Willis.  The  circle  is  composed  of  the  tip  of 
the  basilar,  the  two  posterior  cerebrals,  the  two  posterior  communi- 
cating, the  tips  of  the  two  internal  carotids,  the  two  anterior  cere- 
brals, and  the  anterior  communicating,  which  connects  the  two 
anterior  cerebrals. 

The  nucleus  caudatus  and  the  nucleus  lenticularis  are  almost 
exclusively  supplied  by  the  middle  cerebral  artery,  whose  branches 
pass  through  the  foramina  of  the  anterior  perforated  space.     The 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS.  SYSTEM.  587 

branches  are  subdivided  into  the  lenticular,  lenticulo-striate,  and 
lenticulo-ihalamic  arteries.  These  vessels  pass  to  their  terminations 
without  anastomosing  with  one  another.  One  of  the  lenticulo-striate 
arteries  which  passes  through  the  outer  part  of  the  putamen  is  very 
frequently  the  seat  of  haemorrhage.  By  Charcot  it  has  been  named 
the  artery  of  cerebral  hemorrhage. 

The  lymph  finds  its  way  out  of  the  various  areas  of  the  brain  by 
means  of  perivascular  spaces  in  the  tunica  adventitia  of  the  blood- 
vessels. These  spaces  communicate  with  the  subarachnoid  space  at 
the  surface  of  the  brain. 

PHYSIOLOGY  OF  THE   NERVOUS   SYSTEM. 

Comparison  of  Nerve  and  Muscle. — In  the  study  of  the  general 
physiology  of  muscle  there  was  first  analyzed  its  most  apparent  phe- 
nomenon: muscular  contraction.  Then  the  forces  which  provoke 
muscular  contraction  were  considered,  with  modifications  of  muscular 
excitability. 

Practically  the  same  course  will  be  adopted  in  treating  of  the 
general  physiology  of  the  nerves.  First  there  will  be  considered  that 
property  comparable  to  the  muscular  contraction;  in  turn  will  follow 
a  study  of  the  forces  which  produce  the  nerve-wave,  with  modifi- 
cations also  of  the  nervous  excitability. 

Thus,  there  will  be  established  a  sort  of  parallel  between  nerv- 
ous and  muscular  functions;  muscular  contraction  and  nerve-wave; 
muscular  irritability  and  nervous  irritability;  muscular  excitability 
and  nervous  excitability. 

When  a  nerve  is  separated  from  its  nervous  centers  and  no  force 
intervenes  to  modify  its  state,  then  it  will  remain  inert.  There  will 
be  neither  movement  nor  sensibility,  ^'either  will  the  nerve  come 
into  action  unless  it  be  stimulated  or  excited. 

Nerve  Excitability. — When  a  stimulus  is  applied  to  a  nerve  it 
enters  into  activity.  There  are  various  ways  in  which  this  activity 
is  manifested,  as  by  modification  of  motion  or  sensation,  and  besides 
these  external  manifestations  a  latent  property  in  the  nerve  itself, 
known  as  negative  variation,  which  it  undergoes  during  activity. 
The  most  striking  exhibit  of  nerve  activity  is  the  contraction  of  the 
muscle  supplied  by  the  nerve.  If  we  would  estimate  the  irritability 
of  a  nerve  it  is  necessary  to  know  accurately  both  the  intensity  of 
the  stimulus  and  the  result  produced.  Irritability  requires  for  its 
due  manifestation  the  integrity  of  the  nerve  and  an  unimpaired  circu- 
lation and  nutrition.    But  even  in  a  normal  state  the  irritability  of  the 


588  PHYSIOLOGY. 

nerve  is  extremely  variable  and  is  in  a  constant  state  of  instability. 
Intervals  of  repose  alternating  with  activity  are  the  most  favor- 
able conditions  for  the  maintenance  of  irritability.  When  a  nerve 
remains  at  rest  for  a  long  time  the  irritability  diminishes  and  may 
even  be  abrogated,  conducing  to  degeneration  of  the  nerve.  Ex- 
cessive stimulation  has  a  similar  effect  to  destroy  the  nerve. 

For  a  proper  appreciation  of  so  delicate  a  structure  as  the 
nervous  tissue  and  the  changes  of  a  fundamental  order  occurring 
within  it,  the  student  should  picture  to  himself  the  physical  condi- 
tion of  the  nerve ;  how  it  is  composed  of  molecules  in  a  state  of  stable 
equUihrium.  With  this  conception  he  will  readily  see  how  any  ex- 
ternal stimulus  may  produce  molecular  movement  in  one  direction 
and  hold  them  in  said  position  for  any  variable  time. 

With  cessation  of  the  exciting  cause  the  molecules  will  be  re- 
leased from  their  rigid  condition  and  immediately  return  to  their 
previous  normal  state.  This  "return"  is  the  occasion  of  changes 
in  the  opposite  direction.  Thus,  any  power  that  is  capable  of  pro- 
ducing movement  in  any  one  direction  is  sure  to  be  succeeded  by 
movement  in  the  opposite  direction  as  the  molecules  of  the  nerve 
resume  their  normal,  stable  equilibrium. 

This  fundamental  principle  must  constantly  be  kept  before  the 
student's  mind,  since  many  of  the  physiological  phenomena  of  the 
nervous  system  are  dependent  upon  it,  or  their  conception  is  mate- 
rially aided  by  remembering  it. 

Irritability  of  Different  Points  of  the  Same  Nerve. — The 
farther  from  the  muscle  the  nerve  is  stimulated,  tbe  higher  will  be  the 
original  irritability.  It  was  upon  this  fact  that  Pfliiger  predicated  his 
erroneous  avalanche  hypothesis:  that  a  nerve-wave  gathers  force  as 
it  passes  along  the  nerve-fiber.  The  true  theory  about  the  fact  is  that 
the  irritability  of  the  nerve  is  elevated  in  the  neighborhood  of  the 
cross-section  by  the  passage  of  the  demarcation  current  through  that 
portion.  It  has  been  shown  by  mechanical  stimuli  that  the  uninjured 
nerve  has  an  equal  irritability  throughout  its  whole  length. 

Effect  of  Heat  on  Nerves. — Any  sudden  change  of  temperature 
acts  as  an  excitant  of  a  nerve.  A  temperature  below  24.8°  F.  or 
above  95°  F.  applied  to  a  motor  nerve  of  a  frog  calls  out  a  contrac- 
tion of  the  muscle. 

If,  however,  a  nerve  be  gradually  frozen  it  will  regain  its  excita- 
bility upon  thawing.  When  a  nerve  is  cooled,  in  the  case  of  the  frog 
the  irritability  persists  for  a  long  time.  If  a  nerve  of  a  frog  is 
heated  to  113°  F.  its  excitability  is  increased  and  then  diminished. 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.  589 

In  the  case  of  a  man  who  plunged  his  elbow  into  a  freezing  mixture, 
so  as  to  greatly  cool  the  ulnar  nerve,  there  was  no  contraction,  but 
])ain  in  the  parts  innervated  by  the  nerve. 

Can  a  Nerve-fiber  be  Fatigued  ? — It  has  been  shown  by  Bow- 
ditch  that  if  you  curarize  an  animal  and  irritate  the  nerve  for 
hours,  when  the  curare  paralysis  of  the  motor  nerve  ends  and  has 
been  removed  a  muscular  contraction  of  undiminished  force  ensues. 


Fig.     2()4. — D,    Uubois-Reymond's    Spring    Myograph     to    Measurt-     the 
Rapidity  of  the  Nerve  Current  in  Motor  Nerves.      (Lahousse.  ) 

P,  Cell.  W,  Pohl's  commutator.  M,  Muscle,  n.  Nerve  irritated  by  an  induc- 
tion nearest  to  muscle.  F,  Writing  pen  attached  to  muscle,  n'.  Nerve  irritated 
by  an  induction  current  farttiest  from  muscle.  B,  Smoked  plate  on  which  are 
recorded  the  movements  of  the  writing  pen  F. 

Inability   to   fatigue   a    nerve-fiber   occurs   in    both   medullated   and 
unmedullated  nerves. 

Tlie  Transmission  of  the  Nerve-ivave. — This  demands  that  the 
nerve-fiber  stimulated  be  entirely  sound.  It  has  the  following  phe- 
nomena :  The  nerve-wave  passes  in  both  directions  in  both  sensory 
and  motor  nerves.  When  a  nerve  is  irritated  by  an  electrical  current 
the  electromotive  phenomenon  of  negative  variation  is  seen  in  both 


590 


PHYSIOLOGY. 


ends  of  the  nerve.  Bert's  experiment  of  fixing  the  end  of  a  rat's 
tail  in  a  wound  in  the  back  and  dividing  the  tail  at  its  root  after 
union  has  ensued  shows  that  the  stiniuhis  is  transmitted  both  ways 
in  the  case  of  sensory  nerves.  When  the  root  of  the  divided  tail  was 
irritated  there  followed  symptoms  of  pain,  showing  that  the  nerve 
impulse  of  sensation  was  transmitted  in  a  direction  op^^osite  to  the 
normal  one. 

This  fact  is  somewhat  difficult  of  explanation,  but  in  support  of 
it  comes  Kiiline's  classical  experiment.  This  investigator  takes  the 
sartorius  muscle  of  a  frog  and  separates  it  lengthwise,  beginning  at 


ct   ih 


/^^/^/^•\/^/\/\/^^/^^ 


Fig.   2()5. — Curves   Illustrating   the  Measurement   of   the   Velocity   of   a 
Nervous  Impulse    ( Diagrammatic ) .      (  Foster.  ) 

To  be  read  from  left  to  right. 

The  same  muscle-nerve  preparation  is  stimulated  (1)  as  far  as  possible  from 
the  muscle  and  (2)  as  near  as  possible  to  the  muscle;  both  contractions  are 
registered  by  the  pendulum  myograph  exactly  in  the  same  way. 

In  1  the  stimulus  enters  the  nerve  at  the  time  indicated  by  the  line  a,  the 
contraction,  shown  by  the  dotted  line,  begins  at  V ,  the  whole  latent  period 
therefore  is  indicated  by  the  distance  from  a  to  V. 

In  2  the  stimulus  enters  the  nerve  at  exactly  the  same  time  (a) ;  the  con- 
traction, shown  by  the  unbroken  line,  begins  at  h\  the  latent  period  therefor  is 
indicated  by  the  distance  between  a  and  h. 

The  time  taken  up  by  the  nervous  impulse  in  passing  along  the  length  of 
nerve  between  1  and  2  is  therefore  indicated  by  the  distance  between  6  and  6', 
which  may  be  measured  by  the  tuning-fork  curve  below. 

N.  B.— No  value  is  given  in  the  figure  for  the  vibrations  of  the  tuning-fork, 
since  the  figure  is  diagrammatic  the  distance  between  the  two  curves,  as  com- 
pared with  the  length  of  either,  having  been  purposely  exaggerated  for  the  sake 
of  simplicity. 


its  extremity,  so  that  two  small  tongues  are  formed.  Each  tongue 
receives  nervous  filaments  from  the  same  peripheral  branch.  If  one 
of  these  small  tongues  be  mechanically  stimulated  the  exciting  state 
of  the  motor  nervous  fiber  is  found  to  be  communicated  to  the  other 
small  tongue.  Since  the  second  small  tongue  was  excited  by  a  motor 
stimulus  to  the  first  one.  it  follows  that  the  conduction  occurred  in  a 
centripetal  direction  along  the  course  of  a  motor  nerve.  This  direc- 
tion is  different  from  that  of  normal  conduction,  for  the  nerve  which 
has  been  thus  excited  is  a  centrifugal  motor  nerve.  Therefore,  since 
the  motor  nerve  has  played  the  role  of  a  centripetal  conductor  in  this 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.  591 

experiment,  it  follows  that  a  motor  nerve  can  conduct  an  excitation 
in  both  directions. 

Swiftness  of  the  Nerve-wave. — Compared  with  the  rapidity  of 
an  electrical  current,  the  nerve-current  is  immeasurably  slow.  In 
the  motor  nerves  of  a  frog  Helmholtz  made  it  about  88  feet  per  second. 
In  the  horse  Chanvean  found  it  to  be  about  227  feet  per  second  in  the 
motor  nerves  of  the  larynx  and  only  2i  feet  in  the  motor  nerves  of  the 
oesophagus.  In  sensory  nerves  the  velocity  of  the  nerve-wave  is 
variable,  but  may  be  put  down  as  150  feet  per  second.  Cold  dimin- 
ishes the  swiftness  of  the  nerve-wave.  If  the  intensity  of  the  elec- 
trical stimulus  is  increased  the  swiftness  is  increased.  The  part  of 
a  nerve  in  a  state  of  an  electrotonus  slows  the  rapidity  of  the  nerve- 
current,  and  this  is  more  perceptible  as  the  duration  and  intensity 
of  the  polarizing  current  increases.  I  have  found  that  stretching  a 
nerve  lowers  the  rate  of  transmission  of  nerve-force.  The  method  of 
Helmholtz  to  measure  the  velocity  of  the  nerve-wave  is  as  follows : — 
He  stimulated  a  motor  nerve  of  a  muscle  and  registered  the  time 
of  its  contraction  after  excitation.  After  a  while  the  same  nerve  was 
stimulated  at  a  point  nearer  its  distribution  with  the  muscle.  Its 
time  was  also  registered.  The  second  time  was  found  to  be  shorter 
than  the  first,  so  that  the  difference  between  it  and  the  preceding  must 
represent  the  time  required  between  the  tw^o  excitation  points  for  the 
transmission  of  the  nerve-wave.  The  distance  between  the  two  stimu- 
lated areas  being  known,  one  can  very  readily  calculate  the  swiftness 
of  the  nervous  action. 

Excitability  and  Conductivity. — Excitability  of  a  nerve  is  its 
ability  to  react  to  the  irritations  received  by  it.  not  only  at  one  spot, 
but  through  its  whole  length.  Conductivity  is  the  property  of  trans- 
mitting through  its  whole  length,  up  to  its  terminal  extremity,  a 
nerve-wave  wdiich  has  been  called  out  l\v  an  irritant.  When  a  part  of 
a  trunk  of  a  sciatic  nerve  of  a  frog  is  submitted  to  the  action  of  carl)on 
dioxide  and  you  stimulate  that  part,  no  contraction  ensues.  But  when 
you  stimulate  the  nerve  above  this  point  a  tetanus  ensues.  Here  the 
nerve-wave  must  travel  through  the  part  affected  by  the  carbon 
dioxide.  Hence  it  is  inferred  that  conductivity  and  irritability  are 
separate  properties  in  a  nerve. 

Excitants  of  the  Nerve. — I^erve-excitants  are  all  those  forces 
which  modify  its  state.  There  are  electrical,  thernuil.  mechanical, 
and  chemical  excitants.  From  the  fact  that  they  may  act  u]ion  a 
nerve  in  any  part  of  its  course,  they  are  frequently  designated  as 
general  stimuli. 


592  PHYSIOLOGY. 

The  above  are  the  excitants  of  the  sensory  and  motor  nerve. 
However,  it  must  not  be  forgotten  that  in  the  normal  being  it  is  not 
these  forces  which  come  into  play  to  stimulate  to  activity  the  motor 


Fig.  266. — Method  of  Studying  Physiological  Electrotonus. 
(Lajiousse.  ) 

P,  Five  Daniell  cells.  R,  Rheocord.  D,  Pohl's  commutator  to  make  either 
ascending  or  descending  current,  e,  e,  Unpolarizable  electrodes.  iV,  Motor 
nerves.  M,  Muscle,  to  be  attached  to  a  myographic  lever.  C,  Induction  current 
which  can  be  sent  to  A  or  B  by  the  commutator  W  with  the  cross  bars  removed. 

Supposing  we  have  a  descending  constant  current  passing  through  the  nerve, 
then  an  Induced  current  will  not  make  the  muscle  contract  when  it  is  applied 
at  A  in  the  extra  polar  anelectrotonic  region  of  the  nerve.  Before  the  passage 
of  the  constant  current  the  induction  current  of  the  same  strength  as  before 
caused  a  minima!  contraction.  On  the  contrary,  an  induced  current  when  sent 
to  B,  that  is.  in  the  katelectrotonic  region  of  the  nerve,  causes  a  maximal  con- 
traction instead  of  the  minimal  contraction  previous  to  the  pas.sage  of  the  con- 
stant current. 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.  593 

nerve.  The  normal  excitant  is  the  physiological  stimulus;  it  is  the 
will.  It  originates  within  the  nerve-centers,  from  where  it  is  trans- 
mitted to  the  motor  nerve.  Any  stimulus  when  applied  to  a  nerve 
causes  the  molecules  in  that  localized  area  to  vibrate  and  so  produce 
certain  electromotive  changes.     By  the  changes  set  up  in  this  par- 


Fig.  267.— Schema  of  Apparatus  for  the  Study  of  the  Law  of  Con- 
tractions in  the  Frog.      (Lahousse.  ) 

P,   Daniell  cells.     C,  Pohl's  commutator.     E  and  E,  unpolarizable  electrodes 
applied  to  sciatic  nerve.     R,  Rheocord. 

ticular  area  of  nerve,  the  contiguous  parts  are  also  necessarily 
brought  into  activity  by  reason  of  nerve-conduction.  By  many 
authors  this  transmission  of  changes  along  the  course  of  the  nerve  so 
as  to  act  as  excitants  is  known  as  the  true  physiological  stimulus. 
Thus,  the  vibrations  in  each  segment  perform  the  function  of  exci- 
tant for  each  succeeding  segment. 


594 


PHYSIOLOGY. 


Electrical  Excitants. — Tliis  form  of  stimulus  is  surely  the 
most  important  to  study  and  is,  perhaps,  the  one  that  is  most  com- 
plex. The  electrical  stimulus  may  consist  of  either  the  constant  or 
interrupted  current.  The  stimulation  of  the  nerve  may  be  direct, 
as  when  the  electrodes  are  applied  to  the  nerve.  There  are  two 
kinds  of  currents  used :  the  induction  current  and  the  galvanic  cur- 
rent.    I  shall  take  up  the  constant  current. 

Electrotonus. — "When  a  constant  current  traverses  a  nerve  it 
alters  its  excitability,  conductivity,  and  electromotivity.  This  is 
called  electrotonus.  The  part  of  the  nerve  affected  by  the  positive 
pole  is  said  to  be  in  a  state  of  aneleetrotonus,  the  part  altered  by 
the  negative  pole  to  be  in  a  state  of  kateleetrotonus.     Intrapolar 


Fig.  268. — Scheme  of  Electrotonic  Excitability. 

The  nerve  (N-n)  is  traversed  by  a  constant  current  in  the  direction  of  the 
arrow.  The  curve  shows  the  degree  of  increased  excitability  in  the  neighbor- 
hood of  the  cathcde  (B)  as  an  elevation  above  the  nerve;  diminution  at  the 
anode  (A)  as  a  depression.  The  curve  i-h-ff  shows  the  degree  of  excitability 
with  a  strong  current;  the  curve  f-e-d  with  a  medium  current,  and  the  curve 
c-b-a  with  a  weak  current.    A,  is  anode.    B,  is  cathode. 


means  between  the  electrodes  or  poles;  extrapolar  is  outside  the 
poles.  Descending  current  is  down  the  nerve  to  the  muscle ;  ascend- 
ing current  is  from  the  muscle  up  the  nerve.  By  the  action  of  the 
constant  current  on  the  nerve-muscle  preparation  at  the  time  of 
making  and  breaking  of  the  same  we  have  the  contraction  law  of 
Pfliiger.  As  an  aid  to  memory  we  shall  call  the  contraction  "yes;" 
no  contraction,  "no." 

Descending  current.  Ascending  current. 

Strength  of  current.  Make.  Break.  Make.  Break. 

Weak Yes  No  Yes  No 

Moderate Yes  Yes  Yes  Yes 

Strong Yes  No  No  Yes 

Explanation  of  PflItger's  Contraction  Laws. — These  laws 
are  explained  by  the  fact  that  a  sudden  increase  of  excitability  at 
the  kathode  at  the  make  of  a  current,  or  a  sudden  change  of  excita- 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.  595 

bility  from  below  normal  to  normal,  or  above,  at  the  break  of  the 
current  at  the  anode,  acts  as  stimuli  to  the  muscular  contraction.  The 
constant  current,  independent  of  the  changes  in  excitability,  lowers 
the  conductivity  of  the  nerve.  With  the  exception  of  the  weakest 
current,  the  conductivity  at  the  kathode  and  the  anode  is  diminished, 
and  with  currents  moderately  strong  the  conductivity  is  blocked. 


^WM^w    - 


(^^1^3-y^ 


-i'V-<^^^yh^ 


^es 


y^i    r^s 


M/'^i/vvvij 


A/  / 


Fig.  269. — Pfliiger's  Law  of  Contraction  or  Nerve-muscle  Preparation. 
Bcs,  Descending  current.    Asc,  Ascending  current. 

The  conductivity  at  the  anode  is  but  little  affected  and  is  much 
higher  than  at  the  kathode,  so  that  at  the  time  of  full  kathodic  block 
the  nerve-impulse  still  freely  travels  through  the  region  around  the 
positive  pole.  With  stronger  currents,  conductivity  at  the  anode 
diminishes  so  much  in  the  intrapolar  region  that  it  blocks  the  nerve- 
impulse,  but  this  is  to  be  looked  upon  as  a  stretching  of  the  diminu- 
tion of  conductivity  which  has  crept  along  the  intrapolar  area  from 
the  kathode. 


596  PHYSIOLOGY. 

With  ascending  current:  1.  If  tlie  current  is  strong,  the  intra- 
polar  anelectrotonic  part  of  the  nerve  loses  its  conductivity,  the 
stimulus  at  the  kathode  at  the  make  is  not  transmitted  to  the  nerve, 
and  no  contraction"  follows.  Loeb  explains  electrotonus  by  an  in- 
creased and  diminished  concentration  of  the  ions  of  calcium  and 
magnesium  at  the  kathode  and  anode.  At  the  breaking  of  the  cur- 
rent the  anelectrotonus  disappears,  stimulation  is  produced  at  the 
anode,  and  the  muscle  contracts. 

3.  If  the  current  is  moderate,  the  conductivity  of  the  anelectro- 
tonic part  of  the  nerve  is  not  much  affected  and  the  stimukis  pro- 
duced at  the  opening  and  closing  of  the  current  is  transmitted  to 
the  muscle,  which  contracts. 

3.  With  weak  currents,  the  stimulation  is  only  active  at  the 
point  farthest  from  the  muscle  and  the  closing  produces  contraction. 

With  descending  current:  1.  With  strong  currents  the  stim- 
ulus at  the  kathode  at  the  make  produces  a  contraction,  as  kathode 
is  nearest  the  muscle,  but  the  stimulation  of  break  at  anode  is  not 
conducted  on  account  of  the  lowered  conductivity  of  the  intrapolar 
anelectrotonic  part  and  the  kathodic  part  is  not  immediately  passable 
after  a  strong  current. 

2.  With  moderate  current,  contraction  ensues  on  the  opening 
and  closing  of  the  current  for  the  same  reasons  as  in  the  case  of  the 
ascending  current. 

3.  AVith  weak  current,  the  onset  of  katelectrotonus  is  a  more 
powerful  stimulant  than  the  disappearance  of  the  anelectrotonus; 
the  eft'ect  of  the  latter  is  too  slight  to  manifest  any  action. 

The  same  law  is  applicaljle  in  the  electrotonus  of  muscle. 

Katelectrotonus  diminishes  eleetromotivity,  while  anelectrotonus 
increases  it. 

Contraction  Laws  in  Man  (Waller). — A  pair  of  electrodes 
cannot  be  applied  to  a  nerve  in  man  so  as  to  send  a  current  in  at 
one  and  out  at  another  point;  so  you  cannot  have  ascending  and 
descending  currents.  One  electrode  must  be  applied  to  a  nerve,  the 
second,  where  convenient,  to  some  other  part  of  the  body.  If  the 
electrode  be  the  anode  of  a  current,  the  latter  enters  the  nerve  by 
a  series  of  points  and  leaves  it  by  a  second  series  of  points;  the 
former  series  of  points  forms  the  polar  zone  or  region,  the  latter  or 
distal  series  of  points  the  peripolar  zone  or  region.  In  such  case  the 
polar  region  is  the  seat  of  entrance  of  current  into  the  nerve,  that 
is,  the  anode ;  the  peripolar  region  is  the  seat  of  exit  of  current  from 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.  597 

the  nerve,  that  is,  kathode.     Practically,  a  kathode  and  anode  exist 
about  each  jjole  in  the  tissues. 

If,  on  the  contrary,  the  electrode  under  observation  is  the 
kathode,  the  current  enters  the  nerve  by  a  series  of  points  which 
collectively  constitute  a  jjcripolar  region  and  it  leaves  the  nerve  by 
a  series  of  points  which  collectively  constitute  a  polar  region.  The 
current  at  its  entrance  into  the  body  diffuses  widely,  and  at  its  exit 
it  concentrates;  its  density  is  greater  close  to  the  electrode,  and  the 
greater  the  distance  of  any  point  from  the  electrodes  the  less  the 
current  density  at  that  point.  Hence  it  is  obvious  that  current  den- 
sity is  greater  in  the  polar  than  in  the  peripolar  region.  Waller 
makes  the  formula  for  man  as  follows: — 

Weak  currejit K.  C.  C.         

Medium  current K.  C.  C.         A   C.  C.         A.  O.  C 

Strong  current K.  C.  C.         A.  C.  C.         A.  O.  C.         K.  O.  C. 

K.  C.  C.  =  Kathodic  closure  contraction. 

A.   C.  C.  =  Anodic  closure  contraction. 

A.    0.  C.  =  Anodic  opening  contraction. 

K.  0.  C.  =  Kathodic  opening  contraction. 

j\Iaking  "yes"  for  contraction  and  "no"  for  rest  we  have : — 

Kathode.  Anode. 

Make.  Break.  Make.  Break. 

Weak  current Yes  No  No  No 

Medium  current Yes  No  Yes  Yes 

Strong  current Yes  Yes  Yes  Yes 

Eeaction  of  degeneration  denotes  the  reaction  of  diseased  nerve 
and  muscle  on  man.  As  regards  the  nerve,  the  reaction  of  degen- 
eration consists  in  the  abolition  of  excitability  to  the  induced  cur- 
rent, while  the  excitability  to  the  constant  current  is  exaggerated; 
the  muscular  contraction  is  also  greatly  prolonged  and  galvano-tonus 
(tonic  contraction)  is  easily  produced.  The  normal  contraction 
formula  just  given  is  departed  from,  the  most  characteristic  feature 
of  this  departure  being  a  reversal  of  the  normal  order  of  appear- 
ance of  K.  C.  C.  and  A.  C.  C.  Xormally,  K.  C.  C.  appears  with  a 
weaker  current  than  A.  C.  C.  In  a  well-marked  reaction  of  degen- 
eration A.  C.  C.  appears  with  a  weaker  current  than  K.  C.  C.  There 
is  no  satisfactory  explanation  of  this  reversal  (Waller). 

The  musical  symbols  <>  (crescendo  and  diminuendo)  indicate 
increase  and  decrease.  They  are  used  in  electrical  formula  to  show 
the  relationship  of  one  reaction  of  muscle  becoming  greater  than 
another.     Thus:   A.  C.  C.  >  K.  C.  C.  ==  the  anodic  closure  contrac- 


598 


PHYSIOLOGY. 


tion  becoming  greater  than  the  kathodic  closure  contraction.  In 
neuralgias  the  anode  is  placed  upon  the  painful  nerve. 

The  Faradic  current  is  a  more  effective  stimulus  to  nerves  than 
a  galvanic  current,  for  the  effectiveness  of  a  current  as  a  stimulus 
depends  not  only  upon  the  total  variations  in  intensity,  but  also 
upon  the  amount  of  such  variation  in  the  unit  of  time;  that  is,  the 
greater  the  rapidity  of  the  total  variation,  the  more  effective  is  the 
current  as  a  stimulus. 

In  the  Faradic  current  the  kathode  is  always  more  active  in  pro- 
ducing contractions.  The  short  duration  of  the  opening  and  closing 
of  the  induction  currents  makes  them  fused  in  eff'ects. 

Electrotonic  Variation  of  Electromotivity. — Electrotonus 
not  only  changes  the  irritability  and  conductivity,  but  also  the  elec- 


TTSTfVe 


Anelecirotonic 
current 


Polarisim 
current 


Ka-telectro  tonic 
current. 


Fig.  270.      (Waixer.) 

tromotivity  of  a  nerve.  If  a  nerve  is  connected  with  nonpolarizable 
electrodes  in  such  a  way  that  its  transverse  section  is  laid  on  one  and 
its  surface  on  the  other,  then  the  galvanometer  will  show  the  pres- 
ence of  a  strong  nerve-current.  If,  now,  a  galvanic  current  is  passed 
through  the  extremity  of  the  nerve  outside  the  unpolarizable  elec- 
trodes, the  polarizing  current  is  established.  The  electrotonic  cur- 
rent in  the  nerve  always  has  the  same  direction  as  the  polarizing 
current. 

In  the  extrapolar  kathodic  region  an  electrotonic  current  is  gen- 
erated when  the  polarizing  current  is  closed.  In  the  anodic  region 
the  electrotonic  current  is  stronger  than  the  kathodic  current. 

These  electrotonic  currents  are  only  found  in  medullated  nerves, 
and  are  only  produced  by  an  electrical  polarizing  current.  ISTon- 
medullated  nerves,  muscles,  and  tendons  do  not  show  them.  The 
electrotonic  currents  are  not  the  action-currents  of  a  nerve,  and 
must  not  be  confounded  with  them. 

The  experiment  of  paradoxical  contraction  depends  upon  elec- 
trotonic currents. 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.  599 

Reflex  Action. — A  motor  reflex  act  is  the  transmission  of  an 
irritation  by  tlie  neuraxon  of  a  sensory  neuron  to  the  dendrons  of  a 
motor  neuron  and  by  its  neuraxon  in  turn  to  the  muscle. 

The  functions  of  the  gray  substance  of  the  nervous  centers  can 
be  known  only  through  reflex  movements;  so  that,  to  study  reflex 
action  is  to  study  the  nervous  centers. 

From  a  knowledge  of  the  principles  of  a  reflex  action  it  will  be 
seen  that  three  stages  must  be  considered :     1.  The  external  excita- 


3 


Fig.  271. — Elementary  Reflex  Arc.  Course  of  Sensory  Impressions 
and  a  Motor  Impulse,  Passing  Through  the  same  Level  of  the  Spinal 
Cord.      ( MoRAT. ) 

1,  Skin.     2,  Sensory  nerve.     3,  Posterior  root  ganglion.     4,  Anterior  root. 
5,  Motor  nerve.     G,   Muscle. 


tion  which  goes  to  excite  the  nervous  centers  through  the  sensitive 
nerves  as  a  medium.  2.  The  excitation  of  the  nervous  centers  which 
receive  the  irritation  and  then  transform  and  modify  it;  through 
the  medium  of  the  motor  nerves  it  is  communicated  to  the  muscles. 
3.  The  contraction  of  the  muscle  thus  innervated. 

Other  Seats. — It  is  not  only  in  the  spinal  cord  properly  so 
called  that  there  are  reflex  acts.  There  are  some  in  the  medulla 
oblongata,  in  the  pons,  and  in  the  gray  parts  of  the  brain. 

The  physiological  study  of  strychnine  shows  what  intimate  con- 


GOO  Piivsi()L(x;v. 

nections  exist  between  the  different  parts  of  the  spinal  cord.  The 
irritation  of  the  periphery  at  any  point  whatever,  being  transmitted 
to  the  spinal  cord  by  a  sensitive  nerve,  goes  to  provoke  at  once  the 
activity  of  the  whole  organ. 

The  initial  stimulation  for  a  reflex  action  may  arise  from  any 
sensory  nerve,  whether  of  special  sense,  touch,  or  visceral  supply. 
But  there  are  some  which  generate  a  more  active  reflex  movement, 
among  which  may  be  mentioned  those  of  the  j)alm  of  the  hand  and 
the  sole  of  the  foot.  The  quality  and  nature  of  the  stimulus  used 
has  an  influence  on  the  reflex.  Thus,  tickling  the  auditory  meatus 
produces  cough;  excessive  sunlight  acting  on  the  retina  cause* 
sneezing.  Stimulation  of  a  sensory  nerve-trunk  in  any  part  of  its 
course  calls  out  a  reflex  action,  but  the  movement  in  this  case  is  much 
less  energetic  and  its  character  altered.  In  such  a  case  the  stim- 
ulation causes  movement  in  one  or  more  muscles,  while  stimulation 
of  the  skin  surface  innervated  by  the  same  nerve  produces  movements 
which  have  a  peculiar  character  of  co-ordination.  To  produce  a 
reflex  action  the  application  of  the  stimulus  must  be  sufficiently 
rapid. 

Any  agent  which  produces  a  slow  and  gradual  change  in  the 
nerve  is  without  effect.  Some  experimentalists  have  found  a  differ- 
ence between  the  reflex  of  chemical  and  of  mechanical  stimulation. 
When  the  reflex  center  has  a  greater  or  less  excitability,  then  the 
stimulation  produces  greater  or  less  results.  Every  center  which 
gives  origin  to  a  motor  nerve  may  be  looked  upon  as  a  reflex  center. 
The  excitability  of  the  reflex  centers  is  increased  when  their  con- 
nection with  the  cerebrum  is  cut  off  or  when  the  latter  centers  are 
inactive.  Hence  after  decapitation,  removal  of  the  brain,  section  of 
the  oblong  medulla,  or  section  of  the  spinal  cord,  the  centers  below 
the  section  have  greatly  increased  activity  in  their  reflexes.  Set- 
schenow  has  shown  that  mainly  in  the  optic  thalami  and  corpora 
quadrigemina  are  seated  centers  inhibiting  the  activity  of  the  spinal 
reflex  centers. 

Eeflex  excitability  is  much  greater  in  young  animals  than  in 
adults.  This  explains  the  quickness  with  which  slight  causes  pro- 
duce convulsions  in  the  infant.  Eeflex  activity  is  greater  in  the 
summer  than  in  the  winter.  Certain  toxic  agents  have  an  effect  on 
the  reflexes.  Thus,  atropine,  bromides,  chloral,  chloroform,  and 
ether  reduce  reflex  activity,  while  strychnine  greatly  excites  it. 
Chloroform  is  poisonous  to  every  living  cell,  whether  of  plant  or  of 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.  601 

animal  life.  Strychnine  is  only  poisonous  to  the  nerve-cell,  not  to 
the  plant-cell. 

Every  time  that  intellectual  action  is  suppressed  then  are  the 
reflexes  more  manifest.  A  person  asleep  has  more  energetic  reflex 
actions  than  a  person  awake.  In  somnambulism  the  action  of  the 
will  is  nearly  suppressed,  while  the  reflex  excitability  of  the  cord  is 
enormously  increased. 

On  the  other  hand,  a  person  by  exercising  a  strong  will  can 
arrest  certain  reflexes.  Thus,  the  conjunctival  reflex  can  be  pre- 
vented by  the  will  of  a  courageous  person.  Up  to  a  certain  point  a 
person  is  able  to  resist  sneezing  or  coughing,  which  are  certainly 
typical  reflex  movements. 

Swiftness  of  Reflex  Actions. — Helmholtz  succeeded  in  meas- 
uring by  the  graphic  method  the  swiftness  of  the  spinal  actions.  B}' 
him  it  was  ascertained  that  the  excitation  travels  in  the  spinal  cord 
at  the  rate  of  about  twenty-four  feet  per  second. 

Laws  of  Reflex  Actions. — They  are  the  law  of  localizatioti 
and  that  of  irradiation.  One  other  accessory  law  will  be  added:  the 
law  of  co-ordination. 

Lair  of  Localization. — If  any  sensitive  region  be  excited,  the 
first  reflex  movement  which  will  be  produced  will  bear  upon  the 
muscles  near  the  sensitive  region  excited. 

Thus,  if  the  foot  of  a  frog  be  very  lightly  touched,  the  muscles 
of  that  foot  will  respond  reflexly.  If  the  conjunctiva  be  touched, 
the  reflex  movement  will  be  in  the  orbicular  muscles. 

Laiv  of  Irradiation. — When  an  excitation  has  produced  a  reflex 
movement  in  the  muscles  of  one  side  by  a  first  degree  of  irradiation, 
there  will  be  reflex  movements  in  the  corresponding  muscles  of  the 
opposite  side.  Cutaneous  constriction  by  cold  applied  to  the  right 
hand  determines  constriction  by  the  vasomotors  of  the  left  liaud  as 
well.     These  are  examples  of  the  type  known  as  transverse  irradiation. 

If  the  excitation  be  more  intense,  the  movement  is  spread  into 
the  muscles  situated  above  and  l)elow  the  point  of  excitation.  This 
represents  the  longitudinal  irradiation. 

Laiv  of  Co-ordination. — The  law  of  co-ordination  or  adaptation 
of  the  reflex  actions  in  decapitated  animals  is  very  striking.  If  a 
drop  of  acetic  acid  be  placed  upon  the  back  of  a  decapitated  frog  the 
animal  will  make  such  movements  with  the  feet  that  it  seems  to 
want  to  free  itself  from  the  substance  which  irritates  it.  They  are 
not  blind  movements,  but  such  as  seem  to  be  adapted  to  an  end  and 
are  co-ordinated. 


602  piiysi()T.()(;y. 

Reflex  Tonus  of  Spinal  Cord. — li  cannot  be  denied  that,  in  the 
nornial  stale,  there  ii^  always  a  certain  spinal  tonus.  That  is  to  say, 
an  active  state  of  the  cord  which  is  provoked  by  sensory  excitations. 
All  of  the  muscles  of  the  organism,  striated  as  well  as  smooth,  are 
always  in  a  state  intermediate  between  relaxation  and  contraction. 
This  state  of  semiconstriction,  of  semiactivity,  is  governed  by  the 
spinal  cord.  When  the  spinal  cord  is  destroyed,  immediately  all  of 
the  muscles  of  the  body  relax  and  their  tonus  ceases. 

Influence  of  the  Blood. — If  a  limb  be  separated  from  the  rest  of 
the  organism,  and,  consequently,  receives  no  nutritive  blood-current, 
the  function  of  the  n-erve  nevertlietess  persists. 

By  making  Stenson's  experiment  (tying  the  abdominal  aorta), 
at  the  end  of  twenty  minutes,  or  an  hour  at  the  most,  it  will  l)e 
found  that  sensibility  and  motility  disappear  in  the  abdominal  mem- 
bers. Though  the  deprivation  of  blood  be  complete,  still  there  is 
preservation  of  the  nervous  activity  for  some  time. 

By  using  on  man  the  ligature  and  then  compressing  the  limb  by 
an  Esmarch  bandage  interesting  observations  upon  the  influence  of 
anaemia  are  made.  During  the  first  twenty  minutes  the  arm  is  sen- 
sitive and  the  cutaneous  excitations  are  plainly  perceived.  Like- 
wise the  motor  nerves  can  still  command  the  movements  of  the 
muscles. 

Soon,  however,  the  sensibility  becomes  obtuse;  the  voluntary 
movements  take  place  only  incompletely,  without  force,  and  slowly. 
Next  the  sensibility  disappears  so  completely  that  the  strongest  elec- 
trical excitations  are  not  felt.  Because  of  the  powerlessness  of  the 
motor  nerves,  the  limb  feels  limp  and  inert  as  if  it  were  completely 
paralyzed. 

This  state  of  death  of  the  nerves,  from  ana-mia,  contrasts  with 
the  survival  of  the  muscles.  The  nerve  dies  before  the  muscle,  but 
much  later  than  the  nervous  centers. 

Exciting  Effects  of  Anaemia. — However  it  may  be,  ansemia, 
which  makes  the  functions  of  the  nerve  finally  disappear,  begins  at 
first  by  overexciting  it.  Thus,  the  first  effects  of  anaemia  are  marked 
by  an  increase  of  excitability.  If  it  be  a  sensory  member,  anaemia 
of  it  provokes  extremely  lively  pains. 

Physicians  have  long  been  acquainted  with  painful  anaemise.  It 
is  anaemia,  not  absolute,  but  relative,  which  is  often  the  cause  of 
intense  peripheral  pains.  Thus,  in  symmetrical  gangrene  of  the 
extremities  (Raynaud's  disease),  which  is  characterized  by  nearly 
complete  cessation  of  the  circulation  in  the  affected  areas,  the  pain 


ANATO:\IY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.  G03 

is   very   acute.      There   is   extreme   liyperaistliesia,    prol)al)ly    due    to 
nervous  anaemia. 


Physiology  of  the  Spinal  Cord  and  its  Nerves. 

The  spinal  cord  represents:  1.  A  great  conductor  whose  extent 
lies  between  the  brain  and  periphery  of  the  body.  Along  it  are 
transmitted  centrifugal  as  well  as  centripetal  actions;  the  former 
carry  volitional  impulses  to  the  muscles,  the  latter  impressions  from 
the  sensitive  surfaces  to  the  brain.  By  reason  of  the  spinal  cord 
having  in  its  composition  innumerable  nervous  cells,  it  becomes  a  co- 
ordinator of  the  actions  which  pass  over  it. 

2.  The  spinal  cord  represents  a  true  iwrvoiis  center.  It  may  be 
either  an  important  center  of  reflex  phenomena  in  that  its  cells  unite 
centripetal  fibers  with  centrifugal  ones,  or  it  may  possess  the  role  of 
acting  as  a  special  center  of  the  special  functions. 

Cord  as  a  Conductor. — The  law  of  Bell  is  enunciated  as  follows : 
"Of  the  roots  which  issue  from  the  spinal  cord,  the  anterior  are  those 
of  motion  and  the  posterior  those  of  sensation." 

This  law  is  very  clearly  demonstrated  by  the  so-called  Miiller 
frog.  If  the  last  four  anterior  spinal  roots  in  the  cauda  equina  of  a 
frog  are  cut  off  at  the  right,  and  the  last  four  posterior  roots  are  cut 
off  at  the  left,  the  animal  after  recovering  from  the  operation  will 
present  interesting  conditions.  The  right  lower  leg  will  be  para- 
lyzed; that  is,  deprived  of  voluntary  motion.  The  left  lower  leg  will 
be  ancBsthetic:  that  is,  deprived  of  sensation,  but  still  possess  motion. 
Therefore,  the  anterior  spinal  roots  are  motor  and  the  posterior  ones 
sensory. 

Irritation  of  the  posterior  roots,  or  of  their  central  stumps, 
determines  sensations.  These  sensations  are  sharp  pains  in  the 
regions  innervated  by  the  particular  nerve.  Excitation  of  the  peri- 
pheral stump  is  without  any  effect. 

Irritation  of  the  anterior  roots,  or  of  their  peripheral  stumps, 
determines  movements.  These  movements  are  of  the  nature  of  con- 
vulsive cramps  in  the  particular  muscles  innervated.  Excitation  of 
the  central  stumps  is  not  followed  b}'  any  effect. 

Cutting  off,  or  the  complete  destruction,  of  the  posterior  roots 
causes  the  loss  of  tactile,  thermic,  and  painful  sensibilities;  also  of 
muscular  sensation  in  the  parts  where  they  are  distributed.  Sec- 
tion of  the  anterior  roots  wholly  paralyzes  the  muscles  innervated  by 
them. 


604 


PHYSIOLOGY. 


Apparent  Contradiction. — In  demonstrating  Bell's  law  there 
occasionally  are  seen  results  which  seem  to  contradict  that  law,  but 
instead  they  really  confirm  it.  It  is  found  that  in  stimulating  the 
anterior  (motor)  root  with  electricity  the  animal  sometimes  gives 
evidences  of  pain.  The  same  thing  may  occu^r  also  after  cutting  it 
in  the  middle  and  then  stimulating,  not  the  central,  but  the 
peripheral  stump.  Bernard  has  explained  the  sensibility  of  the 
anterior  root  by  admitting  that  the  recurrent  sensitive  fibers,  which, 
taking  their  departure  from  the  posterior  roots,  run  back  from  the 
periphery  towards  the  center  on  the  anterior  root.  If  the  posterior 
root  be  cut  near  to  the  spinal  cord,  sensibility  in  the  corresponding 
anterior  root  wholly  disappears. 


Fig.  272. — Diagram  of  the  Roots  of  a  Spinal  Nerve,  Showing  Effect 
of  Section.      (Landois.) 

The  black  represents  the  degenerated  parts.  A,  Section  of  the  nerve-trunk 
beyond  the  ganglion.  li.  Section  of  the  anterior  root.  C,  Section  of  the  poste- 
rior root.  D,  Excision  of  the  ganglion,  a,  Anterior  root,  p,  Posterior  root. 
g.  Ganglion. 

The  spinal  roots  united,  those  of  sensation  with  those  of  motion, 
constitute  the  inixed  spinal  nerves.  They  furnish  the  different  parts 
of  the  body  in  which  they  are  distributed  with  both  sensibility  and 
motion.  Consequently  the  section  of  many  spinal  nerves  leads  to 
anaesthesia  and  paralysis  of  the  parts  innervated.  In  the  recently 
cut  nerves,  the  central  as  well  as  peripheral  stumps  are  excitable  by 
stimulants,  the  former  causing  pain,  the  latter  contractions. 

Ganglion. — The  posterior  root,  before  joining  the  anterior, 
has  a  ganglion.  The  function  of  this  ganglion  is  its  trophic  infiu- 
ence,  discovered  by  Waller  and  afterward  proved  by  Bernard  and 
others.  When  an  anterior  root  is  cut  the  peripheral  stump  becomes 
atrophied,  whereas  the  central  stump  remains  entire.  The  latter 
retains  its  vitality,  since  it  is  still  in  connection  with  its  trophic 
center  in  the  cells  of  the  anterior  horn  of  the  gray  matter. 

On  the  contrary,  when  a  posterior  root  is  cut  between  the  spinal 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.  605 

cord  and  the  ganglion  the  peripheral  stump  remains  entire,  while  the 
central  stump  becomes  atrophied.  The  ganglia  of  the  posterior 
spinal  roots  have,  therefore,  the  office  of  trophic  centers  over  the 
sensory  nerves;  the  trophic  centers  for  the  motor  nerves  lie  within 
the  cord  itself  and  are  none  other  than  the  large,  multipolar  cells  of 
the  anterior  horns. 

The  anterior  roots  contain  different  centrifugal  fibers — motor 
fibers,  vasomotor  fibers,  sweat,  and  inhibitory  fibers  of  the  splanch- 
nics.  The  motor  fibers  take  their  origin  in  the  cells  of  the  anterior 
horns,  while  other  centrifugal  fibers  are  united  to  the  cereln-al  cortex. 
As  to  the  vasomotor  fibers,  they  have  their  centers  of  origin  in  the 
medulla  oblongata  and  cord  to  penetrate  the  anterior  roots.  They 
probably  do  this  without  entering  into  connnunication  with  the  cells 
of  the  anterior  horns. 

The  posterior  roots  have  centripetal  reflex  filjers.  These  leave 
the  skin,  muscles,  and  other  organs;  penetrate  the  spinal  cord;  and 
are  in  direct  connection  with  the  reflex  centers  located  partly  in  the 
cord  itself  and  partly  in  the  medulla  oblongata,  pons,  corpora  quadri- 
gemina,  cerebellum,  and  optic  thalami.  The  other  sensory  and 
sense  fibers  penetrate  the  cord  by  way  of  the  posterior  roots  to 
ascend  toward  the  cerebral  cortex.  Here  are  received  the  several 
conscious  sensations :  touch,  pressure,  temperature,  pain,  and  mus- 
cular sense. 

Path  of  Transmission  of  Voluntary  Motion. — Voluntary  luotor 
excitation  is  transmitted  from  the  cerebral  cortex  to  the  nerve-cells 
of  the  anterior  horns  by  way  of  the  anterior  and  lateral  colunms. 
These  columns,  as  a  whole,  do  not  participate  in  conduction,  but  only 
the  anterior  pyramidal  tracts  of  the  anterior  columns  and  the  crossed 
pyramidal  tracts  of  the  lateral  columns. 

As  the  student  knows,  the  crossed  pyramidal  tracts  do  not  decus- 
sate in  the  cord,  but  in  the  medulla  oblongata.  The  direct  pyramidal 
tract  does  not  decussate  in  the  medulla,  but  in  the  spinal  cord  by  way 
of  the  anterior  commissure. 

"When  the  spinal  cord  is  completely  sererrd  the  voluntary  move- 
ments for  all  of  the  muscles  below  the  point  of  section  are  ahsoJutcIy 
abolished. 

Path  of  Conscious  Sensations. — The  sensations  of  touch  and 
muscular  sense  are  transmitted  I)y  the  posterior  roots  and  traverse 
the  posterior  columns  to  the  brain. 

Muscular  sense  is  transmitted  mainly  by  the  posterior  columns. 
The  direct  cerebellar  tract,  and  probably  Gowers's,  also  contain  fibers 


606  PHYSIOLOGY. 

which  conduct  muscle-sense  to  the  cerebellum.  Tactile  and  muscular 
sensations  are  abolished  by  locomotor  ataxia. 

One-sided  section  of  the  posterior  and  lateral  columns  causes : 
(a)  suppression  of  skin  sensations,  or  ana3sthesia,  in  the  whole  half 
of  the  body  innervated  by  nerves  which  enter  the  cord  below  the  side 
of  section;  (b)  loss  of  motion  on  side  of  section.  There  is  very  fre- 
quently observed  on  the  side  of  hemisection  a  zone  of  liypera^sthesia ; 
this  is  due  either  to  removal  of  inhibition  on  that  side  or  inflamma- 
tory irritation  of  the  central  extremity  of  the  cut  curd. 

It  has  been  shown  by  WoroschilofE  in  Ludwig's  laboratory  that 
the  lateral  columns  are  a  pathway  for  sensory  impulses.  1  have 
shown  with  Dr.  Eobert  M.  Smith  similar  results  in  a  series  of  sections 
of  the  lumbar  part  of  the  spinal  cord. 

Section  of  the  posterior  and  lateral  columns  does  not  exercise 
any  influence  upon  sensibility  to  pain  and  temperature.  But  this 
is  not  the  case  when  the  gray  matter  is  cut;  so  that  it  must  be 
inferred  that  these  impulses  ascend  through  the  gray  substance  to 
the  brain. 

kSyriufjoiiri/rlia  is  the  term  applied  to  that  condition  when  there 
is  complete  abolition  of  the  conduction  of  pain  and  temperature.  It 
is  due  to  vacuolation  of  the  gray  matter  of  the  cord. 

Fibers  from  the  Centers  of  the  Medulla  Oblongata. — The 
vasomotor  nerves,  which  come  from  a  center  seated  in  the  medulla 
oblongata,  run  down  the  lateral  colnnm  to  penetrate  the  gray  sub- 
stance and  anterior  roots.  Hence,  section  of  the  lateral  columns 
produces  a  dilatation  of  the  arterioles  innervated  by  vasoconstrictors, 
which  leave  the  cord  below  the  point  of  section. 

The  nerves  leaving  the  respiratory  center  also  run  through  the 
lateral  columns  and  enter  the  gray  substance,  to  communicate  with 
it  and  leave  by  the  anterior  roots. 

In  the  middle  third  of  the  lateral  columns  I  have  found  running 
both  sweat  and  inhibitory  fibers.  Both  sets  of  fibers,  I  have  discovered, 
decussate :    the  former  in  the  spinal  cord,  the  latter  in  the  medulla. 

Skin  Reflexes. — The  most  important  slin  reflexes  in  man  are : — 

1.  The  Plantar  Eeflex,  wliich  is  caused  by  tickling  the  sole 
of  the  foot.    The  involved  center  lies  in  the  lumbar  cord. 

2.  The  Cremasteric  Eeflex. — If  the  skin  of  the  upper  and 
inner  surface  of  the  thigh  in  man  be  excited,  the  corresponding 
testicle  will  be  seen  suddenly  to  rise  by  contraction  of  the  cremaster 
muscle.     Its  center  lies  between  the  first  and  second  lumbar  nerves. 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.  607 

3.  The  Abdominal  Reflex  is  a  contraction  of  the  abdominal 
muscles  caused  by  a  t^harp  push  of  the  finger.  Its  center  lies  between 
the  eighth  and  twelfth  dorsal, 

4.  The  Epigastric  Keflex. — If  the  skin  between  the  fourth, 
fifth,  and  sixth  intercostal  spaces  be  irritated,  contractions  of  the 
rectus  alxlominis  of  the  same  side  will  follow.  The  center  is  between 
the  fourth  and  eighth  dorsal. 

5.  Scapular  Keflex. — xA.n  irritation  of  the  skin  covering  the 
scapulge  may  cause  contraction  of  the  shoulder-muscles.  Its  center 
is  between  the  seventh  cervical  and  second  dorsal  nerves. 

Tendon  Reflexes. — 1.  Ankle-clonus. — When  the  sole  of  the 
foot  is  pressed  upon  by  the  hand,  then  the  gastrocnemius  contracts, 
and  if  the  pressure  is  continued  there  may  be  several  clonic  contrac- 
tions.   Ankle-clonus  is  never  found  in  health. 

3.  Patellar  Reflex. — AYhen  a  tap  is  made  on  the  tendon  of 
the  quadriceps  just  below  the  patella,  the  foot  jumps  upward. 

Jendrassik  found  tliat  the  patellar  reflex  could  be  increased  if, 
at  the  time  of  tapping  the  tendon,  the  patient  squeezed  his  hands 
together  or  clenched  his  jaws.  This  augmentation  has  been  called, 
by  Mitchell  and  Lewis,  reinforcement  of  the  knee-jerk.  Bowditch 
and  Warren  found  that  if  the  reinforcing  act  preceded  the  blow  on 
the  patellar  tendon  by  0.6  second,  the  knee-jerk  was  inhibited  instead 
of  being  increased.  Both  reinforcement  and  inhil)ition  of  the  reflex 
are  supposed  to  be  due  to  "overflow"  in  the  central  nervous  system. 
When  the  cortical  motor-center  for  the  foot  of  a  rabbit  was  irritated, 
then  the  patellar  reflex  caused  by  stimulation  of  the  paw  was  in- 
creased, as  shown  by  Exner. 

The  knee-jerk  is  absent  in  locomotor  ataxia,  and  exaggerated  in 
lesions  of  the  brain  and  of  the  lateral  columns  of  the  cord.  This 
exaggeration  is  due  to  removal  of  inhibitory  impulses  from  the  brain 
travelling  down  the  middle  third  of  the  lateral  columns,  as  I  have 
shown  in  the  case  of  the  ano-spinal  reflex. 

Antagonistic  Muscles. — Sherrington  has  shown  a  relation  to 
exist  between  the  tonic  condition  of  antagonistic  muscles;  for  ex- 
ample, between  the  hamstrings  and  the  vastus  internus  of  the  quadri- 
ceps extensor.  Division  of  the  hamstring  muscles,  or  even  section 
of  their  nerv^e,  causes  a  great  increase  in  the  knee-jerk,  elicited  by 
tapping  the  patellar  tendon.  Stretching  the  liamstring  muscles  or 
•weak  stimulation  of  the  central  end  of  the  cut  nerve  to  the  ham- 
string, abolishes  the  knee-jerk.     Every  sensory  irritation  which  calls 


608  PHYSIOLOGY. 

out  a  contraction  of  one  set  of  muscles  will  inhibit  the  antagonistic 
muscles. 

Sherrington  has  shown  that  the  reflex  arc  in  the  knee-jerk  is 
due  to  nerve-fibers  passing  to  and  from  the  quadriceps  extensor  by 
the  anterior  crural  nerve,  and  to  those  passing  to  and  from  the  ham- 
string muscles  by  the  sciatic. 

The  tendon  reflexes  are  not  true  reflexes,  but  are  due  to  a  direct 
stimulant  action  on  the  muscle  itself.  But  a  reflex  arc  is  necessary 
to  keep  the  muscles  in  a  state  of  tonus  that  the  t-endon  reflexes  may 
take  place. 

Centers  in  the  Spinal  Cord. — The  spinal  cord  presides  over  the 
movements  of  the  anus,  the  bladder,  and  the  genital  apparatus  by 
means  of  three  centers  located  one  above  the  other. 

The  ano-spinal  center  is  found  in  the  dog  near  the  fifth  lumbar 
vertebra.  From  this  center  emanate  fibers  which,  with  the  sacral 
nerves,  go  to  animate  the  sphincter  of  the  anus.  Irritation  of  this 
center,  especially  by  disease,  brings  on  spasm  of  the  sphincter,  with 
difficulty  in  passing  faeces.  Destruction  of  the  center  causes  paralysis 
of  the  sphincter  and  incontinence  of  faeces. 

In  paraplegics  (those  afi^ected  with  paralysis  of  the  lower  limbs 
from  cord  lesion),  spinal  incontinence  or  the  involuntary  passage  of 
the  fgeces  may  be  observed.  Or  there  is  a  protracted  and  invincible 
constipation.  The  former  condition  depends  upon  the  destruction 
of  the  spinal  center,  while  the  latter  comes  from  paresis  of  the  intes- 
tine in  the  region  of  the  colon  and  rectum. 

The  vesicospinal  center  in  dogs  is  found  between  the  third  and 
fifth  lumbar  vertebra.  When  it  is  stimulated  or  the  nerves  which 
take  their  departure  from  it,  there  are  energetic  and  painful  contrac- 
tions of  the  body  and  neck  of  the  bladder. 

In  apoplectics  there  is  often,  first,  ischuria  (retention  of  urine), 
which  seldom  comes  from  irritative  or  nervous  spasm  of  the  sphincter, 
but  more  frequently  from  paralysis  limited  to  the  detrusor  nerves 
only.  Afterward  there  is  enuresis  (incontinence  of  urine),  from 
paralysis  also  of  the  nerves  of  the  sphincter. 

The  genito-spinal  center  is  to  be  found  in  the  spinal  cord  at  the 
level  of  the  fourth  lumbar  vertebra.  If  excited  by  stimuli  it  pro- 
duces contractions  of  the  lower  part  of  the  rectum,  bladder,  and,  if 
the  animal  be  a  female,  the  uterus.  In  addition,  if  the  spinal  cord 
be  cut  between  the  dorsal  and  lumbar  parts,  tickling  of  the  mucous 
membrane  of  the  glans  penis  of  the  dog  determines  by  reflex  action 
an  erection.     Erection  is  no  longer  obtained  if  the  lumbar  cord  be 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.  609 

destroyed.  Goltz  and  Freusburg  have  observed  in  a  bitch,  wliose 
spinal  cord  was  cut  at  the  level  of  the  last  lumbar  vertebra,  the  mani- 
festations of  desire,  conception,  gestation,  delivery,  and  lactation  to 
take  place  just  as  in  a  sound  bitch. 

In  obstetrical  wards  women  are  delivered  while  in  the  anaes- 
thetic sleep  produced  by  ether,  chloroform,  or  other  anaesthetics. 

These  various  facts  show  that  the  center  of  the  movements  of 
the  uterus  is  found  in  the  spinal  cord,  and  not  in  the  hrain. 

The  sudorific  centers  are  seated  in  the  spinal  cord.  The  spinal 
cord  has  minor  vasomotor  centers  for  the  vessels  of  the  parts  it  inner- 
vates. In  fact,  cutting  the  cord  produces  hyperipmia  and  eleva- 
tion of  temperature  in  the  paralyzed  parts.  This  is  due  to  the 
paralysis  of  the  vessels  there.     The  constrictors  are  paralyzed. 

Electrical  excitation  of  the  peripheral  stump  lowers  the  tem- 
perature in  the  parts  innervated,  by  constricting  the  lumen  of  the 
corresponding  arterioles.  The  vasomotor  fibers,  emanating  from  the 
spinal  column,  rejoin  the  vessels  either  directly,  or,  more  commonly, 
by  means  of  branches  of  the  SA'mpathetic. 

The  cilio-spinal  center  is  seated  in  the  medulla  oblongata  and 
sends  fibers  down  the  dorsal  cord  to  the  third  dorsal  vertebra.  These 
fibers  emerge  by  the  anterior  root  of  the  two  lower  cervical  and  the 
two  upper  dorsal  nerves  and  go  into  tlie  cervical  sympathetic  to  the 
dilating  fibers  of  the  iris.  Pinching  the  skin  of  tlie  neck  will  dilate 
the  pupils :    another  skin  reflex. 

Physiology  of  the  Medulla  and  its  Nerves. 

The  medulla  oblongata,  or  huJh,  like  the  spinal  cord,  is  an  organ 
of  transmission,  or  conduction-,  but  at  the  same  time  it  is  a  center  of 
particular  and  very  important  functions. 

Double  Conduction. — Like  the  spinal  cord,  the  medulla  carries 
centripetal,  or  sensory  actions,  and  centrifugal,  or  motor  actions. 
The  former  are  conveyed  by  means  of  its  posterior  part;  the  latter 
by  the  anterior  part. 

The  centripetal,  sensory  conduction  is  crossed  or  decussated 
along  the  floor  of  the  fourth  ventricle.  The  centrifugal,  motor 
conduction  accomplishes,  instead,  its  decussation  in  the  pyramids  of 
the  medulla,  where  the  right,  lateral  fibers  pass  to  the  left,  and  vice 
versa.  This  decussation  of  the  fibers  is  much  more  complete  in 
man  than  in  animals.  So  much  is  this  so  that  in  man  a  lesion 
which  destroys  one-half  of  the  medulla  brings  on  complete  hemi- 
plegia of  the  opposite  side ;    in  animals  a  similar  lesion  never  pro- 


010  PHYSIOLOGY. 

duces  hemiplegia,  but  only  paresis.  Equally,  in  animals  this  same 
lesion  does  not  entirely  abolish  sensibility  in  the  opposite  side  of  the 
body.  The  gray  substance  of  the  opposite  side  connects  the  parts 
lying  over  and  under  the  lesion,  and  so  conducts  the  sensory  im- 
pressions. 

Bulbar  Nerves. — From  the  medulla  oblongata  many  pairs  of 
nerves,  the  bulbar  nerves,  take  their  origin  and  departure.  Each  nerve 
has  a  gray  nucleus.  The  nuclei  on  the  right  side  are  connected  with 
those  on  the  left  and  all  have  their  location  along  the  gray  substance 
of  the  floor  of  the  fourth  ventricle.  The  fibers  which  connect  these 
nuclei  of  origin  with  the  superior  cranial  centers  are  also  crossed  on 
the  way. 

Centers. — The  medulla,  with  its  gray  substance  and  especially 
with  the  gray  nuclei  of  the  nerves  which  issue  from  it,  becomes  a 
center  of  very  important  functions. 

First,  it  is  a  respiratory  center.  This  center  is  found  toward  the 
inferior  angle  of  the  fourth  ventricle,  a  little  back  of  and  lateral  to 
the  source  of  the  vagi  nerves.  It  is  composed  of  two  lateral  halves, 
each  of  which,  in  function,  can  take  the  place  of  the  other.  This 
center  is  about  two  and  one-half  millimeters  in  size. 

A  lesion  affecting  both  respiratory  centers  causes  the  sudden 
death  of  a  warm-blooded  animal.  Therefore,  this  region  of  the 
fourth  ventricle  has  l)een  called  the  vital  Tcnot.  In  fact,  a  blow  from 
a  stick  upon  the  back  part  of  the  head  or  upon  the  nape  of  the  neck, 
also  a  thrust  from  a  sharp  stilleto  between  the  back  of  the  head  and 
the  first  vertebra,  suffices  to  cause  even  a  large  mammal  to  fall  to  the 
ground  instantly.  Butchers  do  this  because  they  injure  the  vital 
knot. 

Components  of  the  Center. — The  center  of  respiration  in  the 
medulla  is  composed  of  an  inspiratory  center  and  an  expiratory  center. 

From  the  inspiratory  center  the  excitation  for  the  nerves,  and 
therefore  for  the  muscles  of  inspiration,  takes  its  departure  rhyth- 
mically. These  motor  excitations  always  decussate  in  the  cervical 
cord.  The  inspiratory  excitation  reaches  the  center  by  means  of  the 
pneumogastric  nerves,  having  been  carried  along  their  sensory  pulmon- 
ary fibers.  The  excitation  is  originated  cither  by  reason  of  an  accumu- 
lation of  CO2  in  the  blood  or  the  absence  of  0.  On  the  contrary, 
an  excess  of  oxygen  in  the  blood  abolishes  excitation  of  the  inspira- 
tory center. 

The  expiratory  center,  on  the  other  hand,  gives  excitation  to  the 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.  gH 

nerves  and  muscles  of  forced  expiration  (normal  expiration  is  accom- 
plished by  reason  of  the  elasticity  of  the  thoracic  case). 

Experimentally  it  is  observed  that  exciting  the  vagus  nerves  or 
their  central  stumps  provokes  very  deep  inspirations  until  tlie  thorax 
stops  in  the  inspiratory  movement. 

Stimulating  the  superior  laryngeal  nerves  or  their  central 
stumps  provokes  violent  and  forced  expirations  until  the  thorax  stops 
in  the  expiratory  movement. 

It  is  said  that  when  a  lesion  affects  the  bilateral  respiratory  cen- 
ter there  follows  immediate  suspension  of  breathing,  and,  therefore, 
death. 


Fig.   273. — Floor   of   Fourth    N'entricle  of  Rabbit.      (Hedon.) 

Puncture  at  «,   a  little  above  the  nib  of  the  calamus,   produces  diabetes. 
Punoture  at  h  produces  polyuria  without  glycosuria. 

The  medulla  oblongata  is  a  moderating  center  of  the  movements 
of  the  heart.  By  irritating  the  medulla  near  the  originating  nucleus 
of  the  vagus  nerve  there  is  caused  a  stoppage  of  the  cardiac  move- 
ments. The  heart  first  slackens  its  systole  and  afterward  stops  in 
diastole.  The  medulla  exercises  this  moderating  action  upon  the 
heart  through  the  vagus  nerve  as  a  medium.  Some  of  its  centrifugal 
fibers  put  themselves  in  relation  with  its  inhibitory  ganglia.  Hence, 
moderation  and  suspension  of  the  heart  movements  is  obtained  by 
irritating  the  peripheral  stump  of  the  vagus  in  the  neck.  According 
to  Traube,  the  normal  stimulus,  capable  of  exciting  this  moderating 
action,  is  the  accumulation  of  CO,  in  the  blood. 

In  the  medulla  is  found  tliis  moderating  center,  whicli  is  antago- 
nistic to  that  other  center  seated  in  the  medulla  oblongata :  the 
accelerator  center  of  the  heart. 

The  medulla  contains  the  principal  vasomotor  center,  which  is  of 


612  PHYSIOLOGY. 

tliG  utmost  importance  to  the  economy.  This  general  vasomotor 
center  in  the  medulla  may  become  stimulated  directly  from  the  hrain. 
In  short,  an  emotion  or  irritation  to  the  cerebral  cortex  readily 
brings  on  ischemia  or  hypensmia  either  in  the  skin  or  in  the  internal 
organs.  Thus,  there  may  be  pallor  from  fear  or  diarrhoea  from 
fright. 

This  organ  of  the  nervous  system  is  a  secretory  center  for  the 
saliva.  In  the  floor  of  the  fourth  ventricle  at  the  level  of  the  origin 
of  the  facial  nerve,  and  somewhat  posterior  to  it,  is  found  the 
originating  nucleus  of  the  fibers  of  the  intermediary  nerve  of  Wris- 
berg.  This,  through  the  chorda  tympani  of  the  facial  nerve,  is  car- 
ried to  the  submaxillary  gland.  Pricking  the  center  or  stimulating 
it  electrically  provokes  a  copious  secretion  of  saliva.  Certain  patho- 
logical lesions  may  produce  the  same  thing. 

Glucose  Secretion. — The  puncture  in  tlie  fourth  ventricle 
should  be  limited  superiorly  by  a  line  joining  the  origin  of  the  audi- 
tory nerves,  and  inferiorly  by  one  Joining  the  origins  of  the  vagi. 
This  will  determine  within  an  hour  the  condition  known  as  diabetes 
mellitus — glucose  in  the  urine. 

The  diabetes  ceases  if  the  liver  be  extirpated,  and  is  not  pro- 
duced if  the  liver  has  been  previously  taken  away,  or  its  vessels  have 
been  previously  tied.  In  the  liver  of  animals  rendered  diabetic  in 
such  a  manner  there  is  found  an  intense  vasomotor  paralysis.  This 
appears  to  be  the  cause  of  the  increased  production  of  glucose. 

The  action  of  the  medulla  upon  the  liver  is  exercised  by  means 
of  the  spinal  cord  through  the  intervention  of  the  great  sympathetic. 

The  oblongata  centers  are :  (1)  respiratory,  (3)  vasoconstrictor 
and  vasodilator,  (3)  cardio-inhibitory ,  (4)  cnrdio-accelerator,  (5) 
diabetic  center,  (6)  vomiting  center.  (7)  deglutition,  (8)  salivation, 
(9)  mastication,  and  (10)  cilio-spinal. 

ANATOMY  OF  THE  CEREBELLUM. 

The  cerebellum  is  situated  at  the  posterior  and  inferior  portion 
of  the  brain. 

It  is  bounded  anteriorly  by  the  cerebrum,  which  is  separated 
from  it  by  the  tentorium  of  the  cerebellum.  At  the  posterior  face 
of  the  cerebellum  are  the  pons  and  medulla  oblongata,  from  which 
structures  it  is  separated  by  the  fourth  ventricle.  The  cerebellum  is 
entirely  covered  by  the  occipital  lobes  of  the  cerebrum  in  man,  but 
only  incompletely  so  in  monkeys.  It  is  united  by  the  cerebellar 
peduncles  to  the  cerebrum,  pons,  and  uiodulla. 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM. 


613 


The  peduncles  are  six  in  number — three  on  each  side.  •  They  are 
known  as  the  superior,  middle,  and  inferior  cerebellar  peduncles. 

Surface  Form. — Tlie  cerebellum  consists  of  a  median  lobe  (the 
vermis)  and  two  lateral  lobes  (the  cerebellar  hemispheres) .  The  supe- 
rior vermiform  process  extends  from  the  notch  on  the  anterior  to  the 
one  on  the  posterior  border. 

The  under  surface  of  the  cerebellum  is  subdivided  into  two 
lateral  hemispheres  by  a  depression  (the  valleij).  It  extends  from 
before  backward  in  the  median  line.  On  the  floor  of  the  median  lobe 
is  the  inferior  vermiform,  process. 


Fig.  274. — Horizontal  Section  Through  the  Cerebellum. 
B.  Stilling.) 


(After 


The  section  passes  through  the  region  under  the  corpora  quadrigemina  (T), 
then  through  the  anterior  cerebellar  peduncle  (/?),  and  between  these  through 
the  lingula  (1).  Above  this  lies  the  nucleus  tegmenti,  nucleus  fastigii  (m),  to  the 
left  of  the  nucleus  globosus  (Xf/),  the  embolus  (Emb),  and  still  farther  to  the  side 
within  the  hemisphere  the  corpus  deutatum  {Vdc). 

Internal  Structure  of  the  Cerebellum. — The  cerebellum,  like  the 
spinal  cord,  is  composed  of  botli  wliito  and  gray  substances.  The  gray 
is  the  most  abundant,  and  occupies  the  periphery  of  the  organ  in 
the  form  of  a  thin  layer  which  is  from  two  to  three  millimeters  in 
thickness. 

The  white  substance  is  placed  in  the  center  of  the  organ  and  is 
enveloped  in  all  of  its  parts  liy  the  gray  matter.    The  white  represents 


614  PHYSIOLOGY. 

nearly  one-third  of  the  whole  cerebellar  mass.  Its  consistency  is 
greater  than  that  of  the  gray  matter. 

The  central  nucleus  of  the  white  matter  sends  out  an  affinity 
of  arborescent  prolongations  which  terminate  in  the  cells  of  the  gray 
substance  of  the  lamella?.  It  is  this  formation  which  the  student  knows 
under  the  name  of  arbor  vitce. 

Each  one  of  the  leaflike  divisions  of  the  white  arbor  vitge  forma- 
tion is  enveloped  by  a  very  thin  plate  of  yellowish  substance,  while 
above  this  is  the  cortical  gray  substance.  The  latter  sinks  into  the 
white  substance  at  the  level  of  the  grooves  which  separate  the  plates 
from  one  another. 

A  horizontal  section  of  the  cerebellum  shows  in  the  center  of 
each  half  of  the  organ  an  ovoid  body.  It  is  very  similar  to  the  olive  of 
the  bulb  in  size  and  structure.    This  is  the  corpus  dentatum. 

Corpus  Dentatum. — The  corpus  dentatum  is  formed  by  a  yellow 
layer  folded  upon  itself  in  the  form  of  a  purse  which  opens  in  front. 
Within  the  interior  of  this  purse  is  found  the  tissue  proper  of  the 
corpus  dentatum.  It  is  formed  of  a  matter  which  seems  to  be  a 
mixture  of  the  white  and  gray  substances. 

Under  the  name  of  accessory  nucleus  dentatus  Meynert  has  de- 
scribed two  small  leaves  of  gray  substance  located  in  front  and  inward 
from  the  corpus  dentatum.  Tliey  are  the  nucleus  globosus  and  nucleus 
fastigii.  Stilling  has  discovered  two  clear  gray  nuclei  at  the  lower 
border  of  the  vermis  near  the  median  line  and  the  roof  of  the  fourth 
ventricle.  He  calls  them  the  nuclei  eniholiformes.  Part  of  the  fibers 
of  the  inferior  cerebellar  peduncles  end  within  these  nuclei. 

Hence,  there  are  here  four  gray  nuclei:  dentate^  globosus,  fas- 
tigii, and  emboliforrnis.  The  last  three  are  in  pairs,  but  the  dentate 
is  single. 

The  central  white  substance  passes  toward  the  lateral  angles  of  the 
sinus  rhomboideus  in  three  prolongations  on  each  side.  They  are  the 
cerebellar  peduncles. 

The  superior  cerebellar  peduncles  go  forward,  and  pass  under 
the  corpora  quadrigemina,  where  they  decussate  with  one  another  in 
the  upper  level  of  the  cereliral  peduncles.  They  end  in  the  optic 
thalamus  and  cortex  of  the  brain. 

The  middle  cerebral  peduncles  pass  forward  and  inward  to  form 
the  superficial  annular  fibers  of  the  ])ons.  These  fibers  form  a  true 
commissure  between  the  two  hemisplieres  of  the  cerebellum;  other 
fibers  decussate  in  the  pons  to  terminate  in  the  islands  of  gray  sub- 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.  615 

stance ;  a  last  category  ascends  into  the  brain  after  decussating  in  the 
pons  Varolii. 

The  inferior  cereheUar  peduncles  (corpus  restiformis)  pass  down- 
ward and  inward  to  the  level  of  the  medulla,  where  the  fibers  which 
form  them  separate  into  three  groups:    the  frst  form  the  external 


Fig.  275. — Section  of  Cerebellum  of  Man  Treated  by  Golgi  Method. 

{ SOBOTTA. ) 

gl,  Glia  cells  of  stratum  cinereum.     A'c,  Basket  cells,     kk::,  Small  granular  cells. 
Rz,  Small  cortical  cells,    sic,  Stratum  cinereum.    stg)-,  Stratum  granulosum. 


arcuaie  fibers  of  the  medulhi ;  the  second  are  thrown  in  to  the  post- 
pyramidal  bodies  (nuclei  of  Coll  and  Burdach)  ;  the  third  are  pro- 
longed directly  into  the  cord  under  the  name  of  direct  cerebellar  tract. 
The  cortex  of  the  cerebellum  is  divided  into  two  layers:  the 
external,  or  molecular  layer;  and  the  interual  granular,  rust-colored, 
or  nuclear  layer.  The  external  layer  is  made  up  of  two  kinds  of  cells: 
star-shaped  and  l)asket  cells.    The  neuraxons  of  tbe  stellate  cells  enter 


616 


PHYSIOLOGY. 


Fig.  276.— Schema  Showing  the  Origin  and  Course  of  the  Fibers  of 
the  Peduncles  of  the  Cerebellum.     (Edixger.) 


ANATO:\IY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.  617 

the  upper  part  of  the  molecular,  or  external,  layer,  forming  a  net- 
work of  fibers.  The  basket  cells  have  their  dendrons  extending  into 
the  inner  part  of  the  molecular  layer,  while  their  neuraxons  arborize 
in  a  tuftlike  manner,  forming  a  '^basket-work"  about  the  cells  of 
Purkinje.  The  internal  layer  is  made  up  of  multipolar  cells  whose 
neuraxons  form  the  horizontal  fibers  in  the  external,  or  molecular, 
layer.  These  horizontal  fibers  divide  in  a  T-shaped  manner,  arbor- 
izing about  the  dendrons  of  the  cells  of  Purkinje. 

In  the  granular  layer  there  are  relatively  large  cells  known  as  the 
cells  of  Golgi;  their  neuraxons  end  in  the  nuclear  layer,  while  their 
dendrons  lie  in  the  molecular  laypr. 

Between  the  external  and  the  internal  layers  we  have  the  cells 
of  Purkinje.  which  are  supposed  to  be  the  cells  concerned  in  the  pres- 
ervation of  equilibrium.  The  dendrons  of  the  Purkinje  cells  occupy 
the  chief  part  of  the  external  layer,  and  have  little,  clublike  projec- 
tions on  them.  The  neuraxons  of  the  Purkinje  cells  go  into  the  in- 
ternal layer,  enter  the  external  layer,  and  arborize  al)out  the  dendrons 
of  the  cells  of  the  latter  layer. 

From  the  white  nuitter  come  fibers,  perhaps  from  the  spinal  cord, 
which  on  entering  the  granular  and  molecular  layers  have  at  their 
terminations  irregular  thickenings;  hence  called  moss- fibers  by  Cajal, 
who  believes  that  they  conduct  impulses  to  the  granular  cells. 

Another  kind  of  fiber  from  the  white  matter,  perhaps  from  the 
spinal  cord,  goes  through  the  granular  layer  into  the  molecular  layer, 
and,  like  a  climbing  plant,  clings  around  the  dendrons  of  the  cells 
of  Purkinje.  and  is  called  the  tendril  fiber. 

Foster  ho'ds  that  impulses  from  the  spinal  cord  or  other  parts 
pass  along  the  tendril  fibers  to  the  dendrons  of  the  Purkinje  cells  and 
by  their  neuraxons  away  from  the  cerebellum  to  other  parts.  But 
other  impulses  may  be  carried  by  the  moss-fibers  to  the  cells  of  the 
nuclear  layer.  From  here  the  impulse  would  be  carried  to  the  mole- 
cular layer  and  spread  along  the  bifurcating  fibrils  a  long  distance, 
which  would  carry  them  to  the  dendrons  of  the  Purkinje  cells.  At  the 
same  time  the  arborizations  of  the  just-mentioned  bifurcating  fibrils 
running  in  a  longitudinal  direction  about  the  basket  cells  would  affect 
the  Purkinje  cells  in  an  indirect  manner,  and.  since  the  neuraxon  of 
each  basket  cell  bears  baskets  for  several  Purkinje  cells,  a  number 
of  these  Purkinje  cells  would  be  "associated"  in  the  same  event. 

The  cerebellum  has  a  threefold  grasp  on  the  cerebro-spinal  axis: 
1.  By  the  direct  cerebellar  tract  and  the  vestibulo-spinal  tract;  by  the 
restiform  bodies  and  inferior  cerebellar  peduncles.     2.  By  the  middle 


618 


PHYSIOLOGY. 


cerebellar  peduncles  connecting  the  nuclei  of  the  pons  and  indirectly 
by  these  nuclei  with  the  frontal  lobes.  3.  By  the  superior  cerebellar 
peduncles  where  the  corpus  dentatum  is  connected  with  the  red 
nucleus  and  where  the  cerebellum  is  connected  with  the  nuclei  of 


y^: 


Fig.  277. — Connections  of  the  Cerebellum  with  Cerebrinn,  Pons,  and 
8pinal  Cord.      (Schema  of  Charpy. )      (Mokat. ) 

1,  Red  nucleus.  2,  Superior  peduncle.  3,  Path  from  cortex  to  pons.  4, 
Middle  peduncle.  5,  Pontal  nucleus.  6,  Inferior  peduncle.  7,  Olive.  8,  Goll 
and  Burdach.     9,  Column  of  Clarke.     10,  Anterior  horn. 


the  optic  thalamus,  and  through  new  neuraxons  of  the  optic  thalamus 
to  the  parietal,  ascending  frontal,  and  ascending  parietal  of  the 
opposite  side.  In  the  red  nucleus  we  have  a  point  of  union  for  im- 
pulses from  the  cerebellum  on  one  side,  and  from  the  cerebrum  on 
the  other  side. 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM. 


619 


PHYSIOLOGY  OF  THE  CEREBELLUM   AND   MESENCEPHALON. 

Cerebellum. — Mechanical  irritation  applied  to  the  cortical  sub- 
stance of  the  cerebellum  does  not  cause  the  animal  to  cry  out  nor  are 
contractions  of  his  members  provoked.  Even  a  prick  or  a  wound  that 
IS  not  very  deep  in  the  cerebellar  cortex  does  not  cause  any  noticeable 
or  constant  disturbances,  particularly  in  movements.  More  often  the 
only  movements  are  those  of  the  ocular  globes. 

However,  a  deep  lesion  of  the  cerebellum — a  large  compression, 
a  tumor,  haemorrhage,  the  removal  of  all  or  a  large  portion  of  the 
cerebellum — determines  a  peculiar  ataxia  which  shows  the  loss  of 
equilibration.  The  animal,  desiring  to  move,  shows  great  uncertainty, 
irregularity,  and  want  of  coordination  of  movement.  Often  when  it 
wishes  to  take  some  steps,  it  falls  backward,  slipping  with  the  feet 
foremost. 


Fig.  278. — Effects  of  Ri'iuoval  of  Cerebellum.      (Daltox.) 

The  experiment  succeeds  best  in  birds.  After  removal  of  the 
cerebellum  they  can  no  longer  keep  their  balance.  This  is  known  as 
cerebellar  tottering.  Sometimes  after  several  efforts  they  succeed  in 
remaining  upon  their  feet  for  a  little  while,  but  they  soon  fall  and 
always  in  a  particular  manner.  They  slip  either  with  the  feet  spread 
wide  apart  laterally,  so  as  to  touch  the  ground  with  the  breast,  or  else, 
slipping  with  the  legs  extended  forward,  they  support  themselves  with 
the  wings  behind.  The  head  is  folded  with  more  or  less  twisting  upon 
the  back.  When  these  animals  continue  to  live  for  some  time  with 
such  a  lesion  they  end  by  presenting  characteristic  obstructions  with 
the  feet,  especially  in  the  disposal  of  the  toes. 

A  man  with  deep  lesions  of  the  cerebellum  has  very  noticeably 
disordered  movements  in  walking  and  standing  erect.  He  cannot  bal- 
lance  himself  well.    While  walking  he  appears  like  one  who  is  drunk. 


620  PHYSIOLOGY. 

He  suffers  intense  vertigo,  with  loss  of  balance,  which  renders  all  wfliis 
movements  ataxic.     This  is  especially  so  of  motions  of  locoir«otion. 

From  this  it  would  seem  that  the  cerebellum  is  the  center  of  the 
coordination  of  movements.  With  the  cerebellum  destroyed,  the  ani- 
mal can  no  longer  balance  itself.  Atrophy  of  one  cereljellar  hemi- 
sphere follows  atrophy  of  the  opposite  cerebral  hemisphere,  showing 
a  close   relation   between   them. 

The  function  of  equilil)ration  is  regulated  by  the  cerebellum, 
which  receives  afferent  impulses  as  follows: — 

1.  Tactile  impressions  by  the  posterior  columns  to  the  nuclei  of 
Goll  and  Burdach  and  from  them  by  the  restiform  body  to  the  cere- 
bellum. To  prove  that  tactile  impressions  are  necessary  to  coordina- 
tion it  is  simply  necessary  to  remove  the  skin  from  a  frog,  when  it 
will  not  be  able  to  leap,  swim,  or  resume  its  natural  position  when 
placed  on  its  back.  Jn  locomotor  ataxia,  where  we  have  a  sclerosis 
of  the  posterior  colunms,  there  is  great  difficulty  in  walking. 

2.  Visual  impressions  by  optic  nerve  conveyed  by  the  superior 
cerebellar  peduncle.  Ataxics  are  able  to  walk  much  better  when  they 
fix  their  eyes  on  the  ground,  and  when  they  close  their  eyes  walking 
becomes  impossible. 

3.  Muscular-sense  impulse  through  the  direct  cerebellar  tract  by 
the  restiform  body  to  the  vermis. 

4.  Impressions  from  the  semicircular  canals,  which  will  be  con- 
sidered under  the  "Semicircular  Canals."  Here  the  vestibular  nerve 
carries  impressions  from  the  semicircular  canals  by  the  restiform  body 
to  the  nucleus  fastigii  and  nucleus  globosus  of  the  cerebellum. 

Horsley  has  shown  that  the  cortex  cerebelli  is  the  afferent 
recipient  organ,  and  that  the  cerebellar  nuclei  and  the  paracerebellar 
or  bulbar  nuclei  are  the  efferent  mechanisms  of  the  cerebellum.  The 
cortex  cerebelli  sends  no  direct  axons  via  the  cerebellar  peduncles 
to  the  brain  or  spinal  cord.  The  cortical  efferent  axons  terminate 
in  the  intrinsic  nuclei  of  the  cerebellum,  that  is,  the  nucleus  den- 
tatus,  nucleus  fastigii,  and  nucleus  emboliformis  vel  globosus.  These 
intrinsic  nuclei  send  efferent  axons  to  the  cerebral,  spinal,  and 
paracerel)ellar,  that  is,  bulbar  nuclei. 

Efferent  Tracts  of  the  Cerebellum. — An  efferent  tract  from 
the  cerebellum  may  be  as  follows:  the  fibers  of  the  superior  pedun- 
cles end  in  the  red  nucleus ;  the  rubro-spinal  tract  runs  from  the  red 
nucleus,  decussates,  passes  through  the  medulla  and  pons,  enters  the 
lateral  column,  and  terminates  around  the  cells  of  the  anterior  horns. 
It  is  also  known  as  Monakow's  bundle.     Another  efferent  tract  may 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.  621 

be  tlie  vestibulo-spinal  tract.  The  nucleus  fastigii  of  the  cerebellum 
has  neuraxons  passing  down  to  the  vestibular  nucleus,  which  is  con- 
nected with  Deiters,  and  these  nuclei  send  neuraxons  down  the  antero- 
lateral columns  to  end  in  the  anterior  horns. 

In  addition  to  the  tottering  walk  and  vertigo,  deep  lesions  of  the 
cerebellum  in  man  produce  a  tendency  to  vomiting.  This  is  probably 
due  to  the  irritation  which  spreads  to  the  center  of  the  origin  of  the 
vagus  nerve  in  the  underlying  medulla  oblongata.  Sometimes  there 
is  found  a  disposition  to  dyspnoea  and  syncope  for  the  same  reason. 
Frequently  there  are  changes  in  the  organ  of  sight,  as  amaurosis, 
strabismus,  and  astigmatism. 

Middle  Peduncles. — Deep  lesion  of  the  middle  peduncles  of 
the  cerebellum  (those  which  pass  to  the  pons  Varolii),  if  made  upon 
one  side  only,  produces  in  the  animal  a  tendency  to  turn  or  rotate 
upon  the  principal  axis  of  its  body.  If  the  lesion  occur  in  the  pos- 
terior part  of  the  peduncle  the  rotation  is  toward  the  side  where  the 
peduncle  is  cut.  The  animal  may  make  as  many  as  sixty  or  more 
revolutions  per  minute.  The  rotation  will  be  toward  the  opposite  side 
when  the  anterior  portion  of  the  peduncle  has  been  injured.  This 
rotation  is  explained  by  Schiff,  who  admits  paralysis  of  the  rotary 
muscles  of  the  head  and  one  side  of  the  spinal  colum. 

Cutting  the  middle  cerebral  peduncle  brings  on  internal  strabis- 
mus in  the  eye  on  the  side  operated  upon,  but  external  superior  stra- 
bismus in  the  eye  upon  the  opposite  side. 

Lesion  of  the  inferior  peduncle  of  the  cerebellum  or  of  the  bulb 
becomes  painful.  Also  the  animal  falls  upon  the  opposite  side  and  is 
unable  to  keep  itself  erect.  The  animal's  body  is  curved  in  the  form 
of  an  arch  toward  the  side  of  the  lesion. 

Lesion  of  the  superior  peduncle  does  not  give  characteristic  and 
precise  phenomena. 

The  Pons. — The  pons  represents  a  crossed  way  of  conductibility 
between  the  periphery  of  the  body  and  the  brain,  and  vice  versa. 
Besides  it  is  a  coordinating  center  of  the  actions  that  pass  through. 
The  pons  Varolii,  at  its  anterior  surface,  shows  itself  to  be  but  very 
little  or  not  at  all  irritable.  Posteriorly,  there  are  signs  of  great 
pain  and  agitation  in  the  animal  under  stimulation.  Deep  irritation 
causes  convulsions  and  pains  according  to  the  kind  of  fibers  irritated. 
The  facial  nerve  is  often  found  paralyzed  upon  the  same  side  as  the 
lesion  and  so  opposite  to  the  paralysis  of  the  members  and  trunk. 
This  condition  is  spoken  of  as  alternate  hemiplegia. 

The  pons  Varolii  is  the  center  of  epileptiform  convulsions.    Deep 


622  PHYSIOLOGY. 

irritation  with  electricity  to  the  suhstance  of  the  pons  causes  general 
cpilej)tiform  movements  in  the  animal,  Nothnagcl,  by  irritating  with 
the  needle,  has  defined  the  limits  of  the  spasmodic  territory,  or  region 
of  cravips.  This  convulsive  center  is  irritated  by  excess  of  CO2  in 
the  blood,  or  else  by  absence  of  the  proper  proportion  of  oxygen.  Oil 
of  absinthe  is  cajiahle  of  irritating  this  center. 

Cerebral  Peduncles. — The  cerebral  'peduncles  contain  all  of  the 
fibers  of  sensation  and  motion  in  the  body  and  direct  them  (except 
a  few)  toward  the  large  ganglia  at  the  base  of  the  brain.  Stimulation 
of  a  peduncle  produces  pain  and  contractions  in  the  opposite  half  of 
the  body;  section  or  deep  lesion  from  disease  produces  paralysis  and 
anaesthesia  in  the  opposite  half  of  the  body. 

The  cerebral  peduncles,  therefore,  carry:  (1)  the  voluntary  exci- 
tations to  the  nerves  of  motion  and  so  to  the  muscles;  and  (2)  the 
sensitive  impressions  made  upon  the  peripheral  extremities  of  the 
centripetal  nerves  up  to  the  brain. 

I  have  found  in  the  cat  that  mechanical  irritation  of  the  locus 
niger  will  cause  the  bladder  to  contract,  indicating  a  high  detrusor 
center.  Mechanical  irritation  of  any  part  of  the  brain  in  front  of  this 
point  has  no  effect  on  the  bladder. 

In  the  greater  number  of  unilateral  lesions  of  the  cerebral  pe- 
duncle the  so-called  movement  in  a  circle  is  oljserved.  That  is,  the 
animal  walks  or  flies,  but  always  follows  the  curve  of  circumference. 
This  is  usually  to  the  side  opposite  the  lesion. 

Corpora  Quadrigemina. — In  man  atrophy  of  the  opposite  anterior 
quadrigeminal  body  follows  removal  of  an  eye.  The  anterior  quad- 
rigemina  are  also  centers  for  the  reflex  movements  of  the  iris.  As  the 
student  already  knows,  the  pupil  contracts  in  the  presence  of  strong 
light,  but  enlarges  in  a  faint  light  or  darkness.  If  the  anterior  quad- 
rigeminal bodies  be  destroyed,  the  pupil  remains  immovable  and 
dilated  even  in  the  presence  of  a  strong  light. 

Besides  these  functions  for  the  eye,  the  quadrigeminal  bodies  are 
believed  to  serve  other  reflex  actions.  The  posterior  quadrigeminal 
bodies  are  pathways  of  auditory  fibers.  They  are  also  regarded  as 
centers  of  coordination  of  movements;  their  destruction  is  accom- 
panied by  disturbances  of  motility. 

Physiology   of  the   Optic  Thalami   and   Striated   Bodies. 

The  optic  thalami,  if  deeply  stimulated  or  injured,  appear  to  be 
but  slightly  irritable  and  little  or  not  at  all  sensitive.  The  animal 
has  shocks  or  shrinkings.  but  does  not  cry  out.     A  deep  lesion,  made 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM.  623 

in  the  posterior  third  of  the  optic  thalamus,  determines  in  the  animal 
movements  in  a  circle  from  the  injured  side  toward  the  sound  side. 
If,  however,  the  lesion  be  made  in  the  anterior  part  of  the  thalamus, 
the  circular  movement  is  reversed. 

Opinion  seems  to  be  divided  as  to  the  effect  produced  by  lesion 
of  the  optic  thalamus  upon  the  visual  function.  It  is  eonchuled,  how- 
ever, that  the  surface  of  the  thalamus  (in  conjunction  witli  the  cor- 
pora quadrigemina)   presides  over  sight. 

In  addition  to  the  functions  just  mentioned,  the  optic  thalami 
have  an  influence  upon  the  sensibility  of  the  opposite  side  of  the  body. 
That  is,  not  conscious  sensibility,  but  that  tactile  and  muscular  sensi- 
bility necessary  for  the  execution  of  extended  and  coordinate  move- 
ments. This  is  especially  so  for  locomotion  without  the  aid  of  the 
will.  These  movements,  then,  are  none  else  than  reflex.  They  re- 
spond to  the  impressions  nuide  upon  the  sensory  surface  of  the  body 
and  reflected  in  the  large,  excitomotor  centers,  viz.,  the  thalami.  The 
thalami  are  relay  centers  for  the  sensory  tract. 

Thus,  while  a  normal  individual  walks  along  a  clear  street,  per- 
haps he  thinks  of  his  movements  but  once.  During  that  short  time 
his  ivUl  directs  his  volitional  impulses;  the  rest  of  his  walk,  on  the 
contrary,  is  executed  almost  automatically.  In  this  case  the  excita- 
tions take  their  departure  from  impressions  upon  the  body  by  the 
ground,  space,  weight  of  the  body,  etc.  These  impressions  are  all 
summed  up  in  the  optic  thalami,  from  which  they  return,  coordinated, 
along  the  nerves  of  motion. 

When  the  striated  bodies  are  irritated  they  do  not  provoke  any 
signs  of  pain.  Though  the  animal  remains  relatively  quiet  under 
ablation  of  the  hemispheres,  yet  it  is  seized  with  violent  and  con- 
vulsive contractions  in  the  opposite  half  of  the  body  when  the  striated 
body  is  hardly  reached.  This  response  is  especially  marked  in  the 
lenticulo-striate  part  of  the  internal  capsule.  By  stimulating  a  striated 
body  with  electricity,  tetanus  in  the  opposite  half  of  the  body  has 
been  obtained.  The  corpora  striata  are  motor  relay  centers.  They  also 
contain  a  thermogenic  center. 

Experimental    Physiology    of    Cerebral    Hemispheres. 

There  are  two  great  means  that  experimental  physiology  has  at 
its  disposal,  viz.:  stimulation  (electrical,  mechanical,  chemical,  and 
thermal)  and  removal.  These  are  likewise  applied  to  the  most  im- 
portant and  noble  part  of  the  nervous  apparatus:  the  cerebral  hemi- 
spheres.    The   experimental  results  are   then  compared  with  those 


624 


PHYSIOLOGY. 


observed  in  clinics  from  pathological  lesions  located  and  circumscribed 
in  various  points  of  tlie  same  hemis])lieres. 

Some  years  ago  all  physiologists  admitted  the  complete  inexcita- 
bility  of  the  cortical  substance  of  the  cerebral  hemispheres.  Accord- 
ing to  the  view  then  held,  mechanical,  thermal,  chemical,  and  elec- 
trical irritation  of  the  convolutions  did  not  determine  phenomena  of 
any  kind. 


Abdomen 
..CheoC 


6  thumbs 


Cidaure 

of  jam.  rt  ■'  ■  , 
Opening 
afj&M 


Voc&L  \ 

corata.    MaAbiceZion 


Fig.  279. — The  Motor  Area  and  its  Subdivisions  on  the  Lateral 
Aspect  of  the  Hemicerebrum  of  the  Chimpanzee.  (GRxmBAUM  and 
Sherrington.  ) 

Later,  however,  it  was  demonstrated  that  very  slight  electrical 
currents  applied  to  the  cerebral  convolutions  in  dogs  determined  vari- 
ous movements  in  the  head,  limbs,  eyes,  etc.  By  this  means  the 
operator  can  cause  the  execution  of  various  movements  to  suit  his 
will,  as,  for  example,  closing  the  fist,  extending  the  arm,  moving  the 
leg,  eyes,  face-muscles,  etc.  These  results  were  best  demonstrated  in 
experiments  upon  apes.  By  experiments  along  this  line  it  has  become 
feasible  to  fix  the  seat  of  various  cortical  motor  centers  of  the  brain. 
In  man  himself  experiments  with  electricity  have  been  made  upon  the 
convolutions  exposed  for  various  causes. 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM. 


625 


Motor  and  Sensory  Centers. 

By  observations  upon  the  chimpanzee,  Sherrington  and  Gruen- 
baum  have  shown  that  the  motor  area  is  in  the  ascending  frontal 
(precentral)  convolution  and  spread  over  its  whole  length.  The  motor 
area  did  not,  at  any  point,  extend  behind  the  fissure  of  Eolando  (cen- 
tral fissure)  ;  on  the  inner  side  of  the  brain  they  found  the  motor  area 
extended  only  a  short  distance  downward,  and  not  to  the  calloso-mar- 
ginal  fissure.    In  the  motor  area  they  also  localized  movements  of  the 

StilcCsnCral.     '^"'^s  St  Vkgina, 
SuZccaUoso  ^^.^-^^        Sa,to.precentr.7tuarg. 

SuLcparieto 


C?  8.  dd. 


Fig.  280. — The  IMotor  Areas  and  Centers  on  the  Mesial   Aspect  of  the 
Hemicerebrum  of  the  Chimpanzee.     (Gruxbaum  and  Sherrington.)    . 

ear,  nostril,  palate,  movements  of  sucking,  mastication,  of  the  vocal 
cords,  of  the  thorax,  abdomen,  and  the  sphincters.  The  arrangement 
of  the  representation  of  various  regions  of  the  muscles  follows  the 
exact  segmental  sequence  of  the  cranio-spinal  nerve  series;  thus,  in 
front  of  the  central  fissure  from  below  upward  are,  first,  the  center 
of  the  face ;  next,  centers  for  the  upper  extremity ;  next,  those  from 
the  trunk ;  and  last,  for  the  lower  extremities.  Extirpation  of  these 
areas  gave  positive  paralysis.  Sherrington  and  Gruenbaum  also 
found  in  the  middle  and  inferior  frontal  convolutions  a  center  which, 
when  irritated,  caused  conjugate  deviation  of  the  eye  of  the  oppo- 
site side. 

In  accordance  with  these  facts  of  Sherrington,  and  from  his 

40 


626 


PHYSIOLOGY. 


clinical  experience,  Dr.  Mills  has  located  the  motor  centers  for  man 
mainly  in  the  ascending  frontal  and  the  paracentral  convolutions. 
The  posterior  central  (ascending  parietal)  is  for  tactile  sensation. 
Muscle-sensibility  is  in  the  superior  and  inferior  parietal  convolu- 
tions. Stereognostic  perception  is  located  in  the  superior  parieta.. 
On  the  mesial  surface  of  the  hemisphere  he  locates  stereognostic  per- 
ception in  the  precuneus.  The  center  of  speech  is  in  the  posterior 
part  of  inferior  left  frontal  gyrus. 


CONCRtTE    CONCEPT 


Fig.  281. — Areas  and  Centers  of  the  I^ateral  Aspect  of  tlie  Human 
Hemicerebrum.      {  Mills.  ) 


In  stereognosis  the  form  of  an  object  is  recognized  l)y  tactile 
sensibility,  although  the  eyes  are  closed.  The  cortical  motor  center 
for  writing  is  seated  in  the  base  of  the  left  frontal  gyrus.  There  is 
clinical  evidence  to  substantiate  the  fact  that  disease  of  the  left  angu- 
lar gyrus  may  cause  agraphia;  for  it  must  be  remembered  that,  in 
order  to  write,  it  is  absolutely  essential  to  call  to  the  mind  memories 
of  the  words  previously  written.  The  center  of  taste  and  smell  is  in 
the  uncus. 

Auditory  Center. — This  center  is  seated  in  the  first  temporal 
convolution  and  in  part  of  the  second.  Complete  deafness  is  not 
produced  in  man  when  there  is  total  destruction  of  one  center,  which 
proves  that  there  is  only  a  partial  decussation  of  the  auditory  jjath- 


ANATOMY  AND  PHYSIOLOGY  OF  NERVOUS  SYSTEM. 


627 


way.     Irritation  of  the  auditory  centers  produces  movements  of  the 
ears,  rotation  and  inclination  of  the  head  as  in  hearing  sounds. 

Visual  Center. — In  man,  the  visual  center  is  in  relation  with  the 
corresponding  half  of  each  retina.  The  destruction  of  one  of  these 
centers  produces  a  bilateral  hemianopsia,  and  not  a  total  loss  of 
vision  in  the  opposite  half  of  the  eye.  The  seat  of  the  visual  center 
is  in  the  cuneus.  The  anterior  part  of  the  visual  center  is  in  rela- 
tion with  the  superior  part  of  the  retina;  the  posterior  portion  of  the 
same  center  is  in  relation  with  the  inferior  part  of  the  retina. 


Fig.  282. — Areas  and  Centers  of  the  Mesial  Aspect  of  the  ±iuman 
Hemicerebrum.      (  Mills.  ) 


Irritation  of  the  occipital  lobes  produces  extensive  movements 
of  the  eyes.  Excitation  of  the  occipital  lobe  always  produces  move- 
ments of  the  eyes,  which  are  directed  to  the  opposite  side :  to  the 
left  when  the  right  occipital  lobe  is  irritated.  It  is  evident  that  the 
occipital  lobes,  whilst  concerned  in  vision,  also  have  efferent  fibers 
to  centers  beneath  the  cortex.  The  center  for  the  memories  of 
objects  seen  is  located  in  the  right  gyrus  angularis.  Ablation  of 
this  area  produces  in  man  mind-blindness;  that  is,  the  person  fails 
to  recall  to  m.ind  the  visual  image  of  the  appearance  of  an  object, 
although  fully  seen.  This  condition  must  not  be  confounded  with 
word-blindness,  which  is  located  in  the  left  angular  gyrus. 


628  PHYSIOLOGY. 

Cortical  Epilepsy.* — Fritsch  and  Hitzig  observed  that,  through 
continued  irritation  of  the  cortex  of  the  cerebrum,  the  animal 
became  convulsed  not  only  in  the  muscles  whose  centers  were 
irritated,  but  in  all  the  muscles  of  the  body.  The  convulsive  move- 
jiient  always  began  in  the  muscles  which  were  innervated  by  the  cen- 
ter irritated,  and  then  spread  from  this  in  a  regular  and  systematic 
manner  to  the  remaining  muscles.  For  exam})le:  when  an  animal 
had  the  left  cortical  center  for  the  eyelids  irritated,  the  convulsive 
movement  began  in  the  muscles  of  the  eyelid  of  the  opposite  side, 
and  then  spread  to  the  other  facial  muscles ;  next,  the  head  was  bent 
to  the  right;  then,  first  the  right  anterior  and  next  the  right  pos- 
terior extremities  were  seized  with  convulsions;  after  this  the  con- 
vulsive movement  began  in  the  muscles  of  the  left  side  and  from 
below  upwards,  first  the  left  posterior  extremity,  then  the  left 
anterior,  and  last  the  muscles  of  the  left  eyelid.  The  convulsive 
movements  are  first  tonic,  and  then  they  become  clonic  aiul  the  ani- 
mal becomes  sleepy. 

If  an  injury  is  produced  in  the  motor  area  and  the  animal  lives, 
then  a  spontaneous  epilepsy  can  ensue  with  cortical  irritation. 

In  the  cortex  of  man  similar  results  ensue  from  an  irritation 
of  the  motor  centers,  except  that  the  man  usually  feels  conscious  of 
the  attacks  in  the  beginning  of  the  fit  and  takes  care  that  he  shall 
not  be  injured  by  the  attack. 

Cortical  epilepsy  can  ensue  from  irritation  of  other  convolutions 
than  the  motor,  but  these  convolutions  must  be  in  a  physiological 
association  with  the  motor  centers.  The  spread  of  the  convulsive 
movements  to  different  muscles  can  take  place  even  after  extirpation 
of  the  opposite  motor  area.  If  the  motor  area  of  a  defined  group 
of  muscles  is  extirpated,  and  on  an  adjacent  motor  area  another 
group  of  muscles  are  convulsed  by  an  irritation,  then  these  convul- 
sions spread  to  the  muscles  whose  motor  area  has  been  extirpated. 
Hence  the  irritation  can  spread  to  the  subcortical  centers  and  cause 
general  convulsions,  even  when  the  original  motor  center  which  has 
caused  the  convulsions  is  extirpated. 

Extirpation  of  the  Motor  Area.* — When  in  a  dog  the  motor  area 
of  one  hemisphere  has  been  extirpated  completely  or  in  part,  then 
shortly  after  the  operation  there  are  considerable  disturbances  of 
the  movements  of  the  opposite  side.  But  soon  the  animal  is  able  to 
move  the  muscles  of  the  opposite  side,  and  after  a  time  the  mus- 


^  Tigei'sted's  "Physiolog\'"  has  been  drawn  upon  for  the  data. 


ANATOMY    AXU    PHVSlOi.OGY    OF    NERVOUS    SYSTEM.         (509 

cular  disturbance  near!}*  entirely  disappears,  except  the  regulation 
of  the  finer  muscular  movements.  Quite  otherwise  is  the  result  when 
you  extirpate  the  motor  area  in  apes.  If  you  remove  the  whole 
motor  area  in  a  monkey  there  is  a  nearly  complete  paralysis  of  the 
muscles  of  arm  and  face,  and  a  weakness  of  the  muscles  of  the  pos- 
terior extremity.  There  is  also  difficulty  in  moving  the  head  to  the 
opposite  side.  The  weakness  of  the  posterior  extremity  is  not  so 
great  but  that  the  animal  can  use  it  in  walking  or  climbing. 

If  in  an  ape  only  the  motor  area  of  the  finger  is  extirpated,  then 
a  permanent  weakness  in  these  muscles  innervated  by  this  area  re- 
mains, whilst  the  other  muscles  are  not  affected.  The  result  of 
irritation  and  extirpation  of  the  cortex  in  the  ape  confirms  the  fact 
that  irritation  of  a  certain  motor  area  always  calls  out  movements 
of  certain  muscles,  Avhilst  extirpation  of  the  same  motor  center  is 
followed  by  a  paralysis  or  weakness  of  the  same  muscles.  The  motor 
area  in  the  ape  is  much  more  important  in  the  muscular  movements 
of  the  body  than  the  motor  area  in  the  dog.  The  subcortical  cen- 
ters in  the  dog  are  not  so  much  under  the  domination  of  the  activity 
of  the  motor  centers  of  the  cortex  as  the  subcortical  centers  in  the 
monkey.  The  motor  centers  in  man  have  been  established  (1)  by 
irritation  of  the  cortex,  (2)  by  anatomical  investigations,  and  (3)  by 
clinical  studies  and  pathological  anatomy.  The  motor  area  in  man 
has  about  the  same  extent  as  in  the  ape. 

Flechsig's  Association  Areas. 

Flechsig,  from  a  study  of  sections  of  56  human  brains,  has 
divided  the  cerebral  cortex  into  36  areas,  of  which  13  are  myelinated 
before  birth.  He  was  able  to  determine  these  areas  by  the  fact  that 
in  the  cerebral  cortex  the  fibers  take  on  myelin  at  different  periods, 
and  thus  he  is  enabled  to  track  the  fibers.  The  sensory  tracts  of  the 
central  nervous  system  take  on  myelin  before  birth.  The  motor 
tract  receives  its  myelin  after  birth,  but  in  the  spinal  nerve  roots  the 
anterior  are  myelinated  before  the  posterior.  The  first  areas  to 
become  myelinated  are  the  sense  areas — smell,  touch,  muscle-sense, 
sight,  hearing,  and  taste.  The  next  series  of  centers  to  become 
medullated  have  at  first  only  fibers  within  themselves — that  is, 
neither  projection  fibers  nor  association  fibers — and  Flechsig  denom- 
inates them  automatic  centers  whose  function  is  unknown.  The 
rest  of  the  areas  have  association  bands,  and  it  is  most  interesting 
to  note  that  the  earlier  areas  of  this  group  develop  as  marginal  zones 
around  the  primary  sensory  areas  and  first  receive  short  fibers  from 


630 


PHYSIOLOGY. 


them.  They  are  without  doubt  connected  with  sensory  areas  in 
function.  The  six  sense  areas  in  the  cortex,  namely,  those  of  smell, 
touch,  muscle-sense,  sight,  taste,  and  hearing,  are  proportional  in 
size  to  the  nerve  or  nerves  supplying  them.  For  example,  the  tactile 
and  muscle  sense  area  is  greatest,  while  the  visual  area  is  larger  than 
the  auditory.  The  structure  of  each  area  corresponds  to  the  struc- 
ture of  the  sense  organ.  Thus  the  visual  area  has  many  layers  of 
cells,  thus  corresponding  to  the  many  layers  in  the  retina.  The 
olfactory  area  has  the  fewest  layers,  thus  being  in  agreement  with 


Fig.  283. — Lateral  View  of  a  Human  Hemisphere,  Showing  the  Bundles 
of  Association   Fibers.      (Starr.) 

A,  A,  Between  adjacent  gyri.  B,  Between  frontal  and  occipital  areas.  0, 
Between  frontal  and  tempora,l  areas,  cingulum.  D,  Between  frontal  and  temporal 
areas,  fasciculus  uncinatus.  E,  Between  occipital  and  temporal  areas,  fasciculus 
longitudinalis  inferior.    C,  N,  Caudate  nucleus.     O,  T,  Optic  thalamus. 


the  cells  of  the  olfactory  mucous  membrane.  The  area  for  hearing 
in  the  cortex  is  twice  as  thick  there  as  in  the  rest  of  the  temporal 
convolution.  Hence  each  area  is  to  be  considered  as  a  repetition,  in 
the  cortex,  of  a  peripheral  sense  organ.  Flechsig  suggests  the  name 
of  projection  fields  for  the  seven  primary  sense  areas. 

As  to  the  great  sense  area  for  touch  and  muscle  sense,  it  is  found 
that  the  sensory  paths  for  the  legs  are  the  first  to  reach  the  cortex, 
and  end  in  the  paracentral  lobule  at  the  upper  third  of  the  ascend- 
ing parietal  convolution,  extending  on  to  the  posterior  surface  of 


ANATOMY   AND   PHYSIOLOGY    OF   NERVOUS    SYSTEM.         631 

the  ascending  frontal  convolution.  The  corresponding  motor  tract 
develops  from  the  area  of  large  pyramidal  cells  in  the  ascending 
frontal  convolution.  Thus  the  sensory  and  motor  areas  in  the  brain 
are  not  mixed,  except  in  the  fissure  of  Rolando. 

The  experiments  of  Sherrington  and  Grlinbaum  on  the  chim- 
panzee are  in  accord  with  the  results  of  Flechsig.  They  found  the 
motor  centers  to  be  in  the  ascending  frontal  convolution,  separate 
from  the  sensory  centers  of  touch  and  muscle-sense  in  the  ascend- 
ing parietal  convolution.  Around  each  primary  sense  area  develops 
a  border  zone  of  association  centers. 

Only  about  one-third  of  the  brain  is  composed  of  sensory  and 
motor  areas;  the  question  arises,  '"What  is  the  function  of  the  other 
two-thirds?"  The  fibers  going  to  the  latent,  inexcitable  area  of  the 
brain  take  on  myelin  much  later  than  those  of  the  excitable  area. 
The  fibers  in  this  latent  area  do  not  run  downward  like  the  projec- 
tion fibers,  but  run  in  a  more  or  less  longitudinal  direction,  and  are 
known  as  internuncial  or  association  fibers;  they  are  of  both  a  cen- 
trifugal and  centripetal  nature.  These  internuncial  fibers  connect 
the  latent  cortex  with  the  excitable  cortex.  According  to  Flechsig 
there  are  three  association  centers:  (1)  the  frontal,  (2)  the  parieto- 
occipito-tcmporal,  and  (3)  the  insular.  These  centers  are  centers  to 
receive  impressions,  and  are  the  seat  of  memory.  The  internuncial 
fibers  are:  (1)  the  superior  longitudinal  bundle  uniting  the  Eolandic 
and  parieto-occip'tal  region;  {2)  the  perpendicular  bundle  passing 
between  the  parietal  lobule  and  the  temporo-occipital  region;  (3) 
the  anterior  association  bundle  connecting  the  frontal  and  temporal 
lobes  and  traversing  the  bottom  of  the  sylvian  fissure;  and  (4)  the 
inferior  association  bundle  uniting  the  temporal  and  occipital  lobes. 
The  frontal  association  center  is  in  front  of  the  ascending  frontal 
convolution ;  the  insular,  or  middle,  association  center  is  the  cortex 
of  the  island  of  Eeil ;  whilst  the  parieto-occipito-temporal  associa- 
tion center  is  situated  back  of  the  ascending  parietal  convolution. 

The  anterior  association  center,  or  frontal,  is  made  up  of  the 
anterior  half  of  the  first  and  a  great  part  of  the  second  frontal  con- 
volution. The  middle  association  center  or  insular  is  covered  by  the 
insula,  whilst  the  posterior  or  parieto-occipito-temporal  is  made  up 
of  the  pra^cuneus,  the  parietal  convolution,  the  second  and  third 
temporal,  and  the  anterior  part  of  all  three  occipital s.  Disease  of 
the  anterior  association  center,  as  in  idiocy  and  dementia,  changes 
the  character;  a  man  of  good  and  orderly  habits  becomes  irritable 
and  disorderly,  and  loses  his  sense  of  morality;    there  is  a  loss  of 


632  niYsiOLOGY. 

ideas  regarding  his  own  personality,  and  his  relations  to  what  is  tak- 
ing place  inside  and  outside  his  body.  He  considers  himself  enor- 
mously wealthy,  or  a  genius,  or  he  iiuiy  fail  to  I'eeognize  liis  own  sur- 
roundings, and  perform  acts  not  reconcilable;  in  other  words,  he  is 
like  one  with  paresis.  When  disease  attacks  the  posterior  associa- 
tion centers  he  is  unahle  to  name  correctly  objects  which  he  can 
touch  and  see,  or,  if  both  centers  are  affected,  he  may  not  at  all 
recognize  the  nature  of  these  objects,  so  that  he  loses  the  power  of 
forming  intelligent  conceptions  of  the  world  around  him.  He  is 
bankrupt  in  ideas,  although  his  affections  may  not  be  altered.  In 
other  words,  he  has  what  is  called  mind-blindness.  The  posterior 
association  center  is  highly  developed  in  musicians. 

PHENOMENA   FOLLOWING  THE   DESTRUCTION   OF   ONE  OR 
BOTH  OF  THE  CEREBRAL  HEMISPHERES. 

Ablation  of  the  cerebral  hemispheres  is  generally  performed  in 
frogs  or  fowls,  who  seem  to  endure  the  operation  sufficiently  well. 
Mammals  easily  succumb. 

The  skin  of  the  head  being  cut  and  the  thin  cap  of  the  skull 
removed,  the  brain  is  reached.  The  incision  of  the  meninges  is  pain- 
ful, but,  after  gradually  removing  the  mass  of  the  hemispheres  from 
above  downward,  the  bird  shows  itself  indifferent.  In  fact,  it  be- 
comes more  stupid  and  apathetic  as  more  of  the  cerebral  tissue  is 
removed.  When  the  removal  of  the  hemispheres  is  completed  without 
injuring  the  peduncular  system,  with  its  ganglia,  and  the  haemorrhage 
stopped  as  well  as  possible,  the  bird  remains  in  a  sleepy  state.  It 
has  a  tendency  to  bury  its  head  and  close  its  eyes ;  it  breathes  slowly, 
but  does  not  walk  away. 

Under  stimulation  the  bird  reopens  its  eyes,  raises  its  head,  takes 
a  few  steps,  then  suddenly  returns  to  its  former  position. 

The  bird,  having  recovered  from  its  traumatism,  the  following 
phenomena  are  observed  within  a  few  days :  The  bird  has  become 
an  automaton.  It  does  not  eat,  so  that  it  becomes  necessary  to  put  the 
food  into  its  mouth.  It  moves  not  at  all  of  its  own  volition;  if  pur- 
sued it  takes  some  steps;  its  pupils  contract  under  the  influence  of 
the  light;  it  cries  or  tries  to  flee  when  the  skin  is  irritated.  It  is 
startled  by  loud  noises.  For  the  rest  there  are  no  longer  voluntary 
movements,  and  the  few  movements  observed  are  aroused  by  external 
excitement,  or  some  internal  need.  The  movements  are  rubbing  the 
skin  with  the  beak,  scratching  the  head  with  the  foot,  etc. 


ANATOMY   AND    PHYSIOLOGY   OF   NERVOUS   SYSTEM.         (533 

The  vegetative  functions  (once  that  eare  is  taken  to  nourish  the 
birds  and  clean  them)  are  performed  without  disturbances.  If  the 
bird  lives  for  some  time  it  shows  a  general  deposit  of  fat.  The  skin 
and  musck's  in  particular  are  seen  to  be  infiltrated  with  adipose 
tissue. 

In  these  birds  there  are  only  movements  of  a  reflex  nature. 

Sensibility  is  blunted  since  the  stimuli  arc  not  able  to  reach  the 
cortical  centers.  Hence,  they  cannot  provoke  volitional  acts  in  them. 
As  Kiiss  says,  these  birds  live,  but  do  not  perceive;  they  hear,  but 
do  not  listen;  they  are  aware  of  stimuli  upon  the  tongue,  but  do  not 
taste  them.  They  are  just  as  a  human  being  who  is  asleep  or  absorbed 
in  contemplation.  He  may  drive  a  fly  from  the  face  without  being 
conscious  of  it. 


Fig.  284. — Effects  of  Ablation  of  Cerebrum.      (Dalton.) 

When  hut  one  cerebral  hemisphere  is  removed  without  in  the 
least  injuring  the  other  and  the  animal  recovers,  it  does  not  show 
positive  disturbances  of  intelligence  or  of  conscious  sensibility  or  of 
voluntary  motion.  However,  the  opposite  side  shows  weakness. 
Should  the  lesion  extend  to  the  underlying  basal  ganglia  or  to  the 
peduncular  system,  there  will  be  complete  hemiplegia  in  the  opposite 
side  of  the  body. 

The  same  manifestations  are  observed  in  a  man  who  has  lost  an 
entire  hemisphere  from  a  wound  or  from  disease.  There  is  no  posi- 
tive lesion  of  intelligence,  but  there  is  manifested  very  marked  fatigue 
from  intellectual  labors.  If  the  lesion  has  extended  toward  the 
peduncular  base  of  the  hemisphere,  there  is  hemiplegia  in  the  oppo- 
site side  of  the  body. 

The  crowbar  case  is  a  much-cited  instance.  A  workman  twenty- 
five  years  of  age  was  engaged  in  charging  a  blast  in  a  rock.  The 
instrument  he  used  was  a  sharp-pointed  bar,  forty  inches  long,  one  and 
one-quarter  inches  in  diameter  and  weighing  twelve  pounds.     The 


g34  PHYSIOLOGY. 

charge  was  suddenly  exploded,  driving  the  bar  so  that  it  entered  the 
man's  lower  jaw  and  came  out  at  the  top  of  the  head  close  to  the 
sagittal  suture  in  the  frontal  region.  It  fell  at  some  distance,  covered 
with  blood  and  brains.  For  the  moment  the  victim  remained  uncon- 
scious. An  hour  after  the  accident  he  walked  to  the  house  of  a  sur- 
geon, where  he  gave  an  intelligent  account  of  the  accident.  For  a 
long  time  his  life  was  despaired  of,  but  he  finally  recovered  to  live 
twelve  and  one-half  years  longer. 

It  may  be  concluded,  therefore,  that  one  cerebral  hemisphere  only 
is  sufficient  for  the  mobility  and  sensibility  of  the  two  sides  of  the 
body,  as  well  as  the  performance  of  psychical  functions.  The  indi- 
vidual with  one  hemisphere  destroyed  remains  like  one  who  has  lost  an 
eye.  That  is  to  say,  the  brain  continues  to  perform  its  functions,  ani- 
mal as  well  as  psychical,  but  with  noticeahle  weahness.  greater  effort, 
and  fatigue.  The  frontal  lobes  are  the  chief  seat  of  the  will,  of  the 
memory,  and  intellectual  functions. 

The  irritahility  of  the  cerebral  cortex  may  be  diminished  or  ex- 
aggerated by  various  circumstances.  Thus,  opium,  ether,  chloroform, 
chloral,  the  bromides,  cold,  asphyxia,  etc.,  diminish  it.  Inflamma- 
tion, urea,  uric  acid,  atropine,  strychnine,  etc.,  increase  its  excita- 
bility. 

Action  of  Brain  Extracts. — In  1898  I  found  that  infusions  of 
dried  brain  reduced  the  heart's  frequency  and  the  arterial  tension. 
Section  of  the  vagus  or  its  paralysis  by  atropine  did  not  prevent  this 
action.  Halliburton  did  not  obtain  the  same  results  after  the  use  of 
atropine,  but  my  experiments  have  been  confirmed  by  Swale  Vincent 
and  Sheen.  Quite  recently  Swale  Vincent  and  Cramer  have  found  two 
substances  in  brain,  both  depressing  the  heart  even  after  the  previous 
use  of  atropine.  They  also  obtained  another  substance  depressing  the 
circulation,  but  its  effects  are  abolished  by  atropine. 

SLEEP. 

Sleep  is  characterized  by  a  suspension  of  consciousness,  a  dim- 
inution of  reflex  activity  of  the  nerve-centers,  a  decrease  of  the 
excitability  of  the  nerves,  and  a  lessening  in  all  the  chief  functions 
of  the  body.  The  activity  of  the  cerebral  motor  centers  is  nearly  sus- 
pended in  the  majority  of  animals  as  they  seek  a  reclining  position. 

In  extreme  fatigue  sleep  is  preceded  by  yawns,  a  want  of  atten- 
tion, a  decrease  of  sensibility  in  the  special  senses,  a  progressive  loss 
of  movement,  and  a  dropping  of  the  upper  eyelids.  The  eyes  are 
closed,  vision  is  necessarily  then  abolished.     The  pupil  is  contracted. 


ANATOMY   AND   PHYWIOLOGY    OF   NERVOUS   SYSTEM.         635 

the  eyeball  is  turned  upward  and  inward ;  at  the  same  time  hearing 
disappears  and  consciousness  vanishes.  During  sleep  the  metabolic 
processes  of  nutrition  are  slowed,  and  there  is  a  diminution  of  the 
heart-beats,  of  the  arterial  tension,  and  of  the  movements  of  respira- 
tion. Sleep  is  deepest  during  the  first  one  and  one-half  hours;  after 
that  its  depth  greatly  diminishes.  Durham  was  the  first  to  show  that 
during  sleep  the  brain  is  anemic,  but  it  is  only  an  epiphenomenon, 
and  not  the  cause  of  sleep.  Plethysmographic  tests  of  the  arm  in 
a  sleeping  person  show  a  decrease  of  volume  whenever  the  subject 
is  disturbed,  although  the  noise  may  not  be  sufficient  to  wake  him. 


Fig.   285. — Curve  of  the   Depth  of   Sleep.      (Piesbergen.)       (From 

Tigerstedt's    "Human    Pliysiology,"  copyright,  1906,  by  D.  Appleton  and 

Company. ) 

Read  from  left  to  right. 

This  means  that  the  brain  is  anemic  during  sleep,  and  that  the 
blood-supply  of  the  brain  is  increased  upon  waking. 

The  histological  theory  of  Demoor  is  that  during  sleep  the  den- 
drons  are  retracted  and  break  the  connections  between  the  dendrons 
and  arborizations  which  are  necessary  for  the  action  of  the  nerve- 
centers,  Demoor  found  that  in  deep  anesthesia  there  were  moniliform 
varicosities  on  the  dendrons.  The  chemical  theory  is  that  during 
wakefulness  certain  fatigue-products  (lactic  acid,  etc.)  are  generated, 
which  have  a  somnolent  effect  upon  the  brain.  If  the  blood  of  an 
exhausted  dog  is  transfused  into  a  dog  awake,  it  will  cause  him  to 
be  fatigued.  It  is  probable  that  the  fatigue  of  the  brain-cells,  the 
law  of  periodicity  of  the  action  of  the  nerve  centers,  and  a  decrease  of 
external  stimuli  are  the  main  causes  of  sleep.  The  intimate  cause 
is  not  known. 


636 


PHYSIOLOCY. 


That  the  absence  of  sensory  impulse  has  an  important  action  in 
promoting  sleep  is  shown  by  the  case  of  a  boy  who  had  only  one  eye 
and  one  ear  to  keep  him  in  touch  with  the  external  world.  All  other 
avenues  of  sensory  impulses  were  abolished.  If  now,  these  avenues  of 
impulse  were  abolished  by  bandaging  the  ear  and  eye,  the  boy  would 
fall  asleep.    If  a  dog  is  kept  awake  five  days  he  will  die.    This  wake- 


-k.--i-:i> 


Fig.  286. — Pyramidal  Cells  of  the  Marmot  in  Two  Difl'erent  Conditions. 
(After  QuERTON.) 

On  the  left,  pyramidal  cell  of  the  marmot  asleep;    on  the  right,  that 
of   the  marmot  awake. 


fulness  is  attended  with  a  lowering  of  temperature  (8°  C).  dimin- 
ished reflex  activity,  and  changes  in  the  brain.  In  man,  loss  of  sleep 
causes  a  slight  increase  in  weight.  The  excretion  of  nitrogen,  and 
especially  that  of  phosphoric  acid,  is  increased  by  the  want  of  sleep ; 
acuteness  of  vision  is  also  increased.  But  when  the  man  is  permitted 
to  make  up  for  this  loss  of  sleep,  there  is  a  complete  disappearance 
of  the  just-mentioned  conditions  and  a  normal  state  ensues. 


ANATOMY    AND   PHYSIOLOGY    OF   NERVOUS    SYSTEM.         637 

NARCOTICS. 

Meyer  and  Overton  have  arrived  at  the  conchision  that  anggsthesia 
is  caused  by  the  solution  of  the  lipoid  (fatty)  constitiients  of  the 
cells  by  the  absorbed  anaesthetic.  All  the .  substances  which  dissolve 
fats  are  anesthetics  if  they  enter  the  cell,  and  anaesthetic  power  is 
proportional  to  this  factor.  The  quick  recovery  which  ensues  when 
the  anesthetic  substances  are  removed  shows  that  the  lipoids  are  not 
taken  out  of  the  cell,  but'  merely  dissolved  within  the  cell.  Wright 
finds  that  anaesthetics  produce  a  disappearance  of  Nissl  corpuscles  and 
a  shrinkage  of  the  nerve-cells  after  prolonged  anesthesia  by  either 
chloroform  or  ether. 

Bromides  and  opium  produce  sleep  by  depressing  the  excitability 
01  the  cortex  cells  of  the  cerebrum. 

CEREBRO=SPINAL  FLUID. 

The  cerebro-spinal  fluid  is  like  a  lymph-fluid.  It  is  only  in  the 
smallest  part  a  transudate,  and  as  such  is  modified  through  the  specific 
secretion  of  the  capillaries  of  the  brain.  It  is  chiefly  a  specific  pro- 
duct of  the  braiu.  It  has  been  shown  that  this  fluid  contains  20  to 
30  per  cent,  of  potash  salts  and  only  15  per  cent,  of  soda  salts,  and 
the  brain  has  also  an  excess  of  potash  compared  with  sodium.  Spina 
believes  that  the  cerebro-spinal  fluid  comes  either  from  its  blood- 
vessels or  the  brain-substance,  and  not  only  from  its  choroid  plexus. 
It  differs  from  the  blood-plasma  in  containing  only  0.2  per  cent,  of 
albumin,  whilst  blood  contains  7  per  cent,  and  Ij'mph  4.5  per  cent,  of 
albumin.  Cerebro-spinal  fluid  does  not  contain,  like  the  blood,  an 
agglutinin  (it  has  no  globucidal  action  on  foreign  blood),  nor  an 
alexin. 

According  to  Allihin,  it  contains  0.0461  per  cent,  of  glucose, 
0.221  per  cent,  of  proteid,  0.2794  per  cent,  of  organic  material, 
0.813  per  cent,  of  inorganic,  98.886  per  cent,  of  water;  peptones  and 
albumoses  were  not  present,  and  the  proteid  seemed  to  be  a  globulin. 

The  cerebro-spinal  fluid  of  diseased  brains  contains  poisonous 
material,  which  results  from  a  disintegration  of  nervous  tissues.  In 
general  paralysis  of  the  insane,  Halliburton  and  IMott  found  a  nucleo- 
proteid  in  the  cerebro-spinal  fluid.  It  is  a  nucleo-proteid,  which, 
when  injected  into  the  circulation,  can  cause  intravascular  clotting. 
The  cerebro-spinal  fluid  and  the  blood  also  contain  choline,  which 
depresses  the  heart.  Ponath  injected  choline  into  the  sensori-motor 
convolution  and  produced  convulsive  attacks.  Choline  is  also  found 
in  other  diseases  of  the  central  nervous  svstem. 


638  PHYSIOLOGY. 

Ether  and  pilocarpin  increase  flow  of  cerebro-spinal  fluid,  whilst 
atropine  slows  it,  and  aniyl  nitrite  has  no  particular  effect.  Medi- 
cines, as  a  rule,  and  the  toxins  of  bacteria,  do  not  appear  in  the 
cerebro-spinal  fluid  when  given  by  the  mouth  or  subcutaneously. 
Strychnia  injected  into  the  cerebro-spinal  fluid  has  a  very  intense 
action,  as  much  as  when  ten  times  that  quantity  is  injected  into  the 
blood.  Cocaine  injected  into  the  cerebro-spinal  fluid  causes  an  anaes- 
thesia in  the  lower  extremities,  lasting  forty-five  minutes.  Whilst 
chemical  substances  with  difficulty  appear  in  the  lymph  when  in- 
jected into  the  blood,  they  appear  quite  readily  in  the  blood  when 
injected  into  the  lymph-tracts. 

REACTION=TIME. 

When  a  terminal  organ  of  special  sense  is  irritated,  the  time 
between  this  stimulation  and  the  moment  when  motion  ensues  as  the 
result  of  conscious  perception  of  the  irritation  is  called  reaction-time. 
Midler's  law  of  specific  energy  of  sensory  nerves  is  that  irritation  of 
nerves  of  special  sense  always  causes  sensations  of  the  same  kind. 
Thus,  when  the  nerve  of  hearing  is  irritated  by  different  agents,  it 
always  gives  rise  to  a  sensation  of  sound.  Perception-time  is  the 
time  required,  for  example,  in  colors,  to  decide  what  color  it  is  and 
in  what  part  of  the  visual  field  it  is  located.  The  organs  of  special 
sense  dift'er  from  each  other  as  to  the  number  of  separate  excitations 
that  they  can  receive  in  a  second.  In  reaction-time  by  the  auditory 
nerve  the  following  things  are  involved:  (1)  the  time  consumed  in 
sound  reaching  the  ear;  (2)  the  time  taken  for  the  reception  of  the 
stimulus  by  the  sensory  terminals  of  the  auditory  nerve  and  the 
transmission  to  the  higher  centers,  so  that  volitional  impulse  may  be 
started  in  the  cerebral  motor  centers;  (3)  the  time  for  the  convey- 
ance of  those  motor  impulses  to  the  nerve-colls  of  tbe  spinal  cord ; 
(4)  the  time  necessary  for  the  generation  of  impulses  in  the  cells  and 
their  transit  down  the  motor  nerves  to  the  muscles  of  the  hand ;  (5) 
the  latent  period  of  the  contraction  of  those  muscles.  The  reaction- 
time  for  sound  is  about  0.150  second;  light,  0.195  second;  and  for 
touch,  0.145  second.  Perception-time  varies  from  about  .01  to  .02 
second. 

THE  GREAT  SYMPATHETIC. 

The  ganglia  lying  on  each  side  of  the  vertebral  column  may  be 
divided  into  four  parts,  viz. :  cervical,  thoracic,  abdominal,  and  pelvic. 

The  cervical  part  of  the  great  sympathetic  is  composed  of  three 
ganglia. 


ANATOMY   AND   PHYSIOLOGY   OF   NERVOUS    SYSTEM.         539 

The  thoracic  portion  is  composed  of  twelve  ganglia. 

The  abdominal,  or  lumbar,  part  consists  of  four  ganglia. 

The  pelvic  portion  consists  of  five  or  six  ganglia,  including  the 
coccygeal  ganglion. 

Two  structures  only  finally  receive  the  sympathetic  fibers;  that 
is,  involuntary  muscular  tissue  and  secretory  epithelium. 

SYMPATHETIC  NERVOUS  SYSTEM. 

The  ganglia  lying  on  each  side  of  the  vertebral  column  are 
lateral  or  vertebral  ganglia.  The  prevertebral  collateral  ganglia  are 
the  ganglia  in  advance  of  the  vertebra,  as  the  semilunar,  inferior 
mesenteric,  etc.  From  the  prevertebral  ganglia,  nerves  go  to  the 
terminal  ganglia  in  the  tissues. 

The  efferent  fibers  of  the  sympathetic  nervous  system  arise  in 
the  intermedio-lateral  column  of  gray  cells.  They  pass  out  by  the 
anterior  root  from  the  spinal  cord.  From  here  they  go  by  the  white 
ramus  to  a  sympathetic  ganglion.  From  the  sympathetic  ganglion 
they  may  pass  in  two  directions:  (1)  they  may  form  synapses 
about  these  cells,  and  from  these  cells  new  axons  (postganglionic 
fibers)  may  arise  and  pass  outwards  in  the  visceral  nerves,  or  back, 
through  the  gray  ramus  connected  to  the  ganglion,  into  the  spinal 
or  somatic  nerve  to  the  blood-vessels  as  vasomotor  nerves,  or  sweat- 
glands  as  secretory  nerves,  or  to  hairs  as  pilomotor  nerves;  (2)  or 
they  may  pass  through  the  ganglion  on  to  one  situated  more  towards 
the  periphery,  in  which  they  form  synapses  and  are  continued 
onward  by  new  axons.  These  ganglia  from  which  they  do  not  pass 
back  to  somatic  nerves  are  called  the  prevertebral  or  collateral  gan- 
glia. These  nervous  fibers,  after  their  interruption,  proceed  as  gray 
nonmedullated  fibers  to  their  termination,  where  they  break  up  into 
a  network  of  anastomosing  fibers,  with  cells  or  a  sort  of  terminal 
ganglion.  When  sympathetic  nerve-fibers  are  interrupted  in  a  gan- 
glion, the  fibers,  before  they  meet  the  ganglia,  are  preganglionic; 
after  they  leave  the  ganglion,  postganglionic.  The  number  of  nerves 
leaving  a  ganglion  is  greater  than  the  number  of  nerves  entering  it. 
If  the  sympathetic  fibers  pass  through  the  vertebral  ganglia  to  be 
interrupted  in  the  prevertebral  ganglia,  then  they  are  preganglionic, 
and  the  fibers  leaving  the  prevertebral  ganglia  are  postganglonic. 
By  nicotine  it  can  be  determined  if  fibers  end  in  a  ganglion  or  pass 
through  it,  for  nicotine  paralyzes  the  preganglionic  terminals  of  the 
nerve-cells  of  a  ganglion,  or,  according  to  Langley,  a  special  recep- 
tive substance  in  the  nerve-cell. 


640 


PIlY!SlUL(HiV. 


Langley  calls  the  sympathetic  system  an  autonomic  system, 
because  it  is  a  sort  of  independent  system  from  the  central  nervous 
system. 


Midbrain  autonomic. 


Bulbar  autonomic. 


■Sympathelic. 
ITh.  to  11  or  111  L.  of  mail 


•Sacral  autouomic. 


Fig.  287. — Diagram  of  the  Origin,  in  Man,  of  the  Efferent  Autonomic 
Fibers  from  the  Central  Nervous  System.      (Langley.) 

The  sympathetic  system  proper  arises  from  the  dorso-lumbar 
cord. 

The  cranial  and  sacral  autonomic  systems  have  more  in  common 
with  one  another  than  either  has  with  the  sympathetic,  and  on  this 
account  they  may  be  grouped  together  as  the  parasympathetic  sys- 
tem.    The  parasympathetic  system  includes  the  midbrain  autonomic 


ANATOMY    AND    PHYSIOLOGY    OF    .NERVOUS    SYSTEM.         (341 

— bulbar  autonomic — and  sacral  autonomic  systems.  The  fibers 
from  the  midbrain  arise  in  it,  and  go  out  in  the  third  nerve  and  by 
the  short  ciliary  nerves  to  the  sphincter  of  the  iris  and  the  ciliary 
muscles,  and  cause  their  contraction.  The  fibers  arising  in  the  bulb 
travel  through  the  facial,  glosso-pharyngeal,  vagus,  and  the  spinal 
accessory. 

Cranial  Ganglia. 

The  ciliary  ganglion  of  the  fifth  cranial  nerve  has  preganglionic 
sympathetic  fibers  from  the  motor  oculi  by  a  short  root  which 
arborize  about  the  ganglionic  cells  and  when  irritated  contract  the 
pupil.  The  postganglionic  fibers  of  this  ganglion  start  from  the 
superior  cervical  ganglion  through  fhe  ciliary  ganglion  to  contract 
the  blood-vessels  of  the  iris  and  retina. 

Caw'tra'l  niert^e  cell. 


Fig.  288.      (Langley.) 

The  number  of  fibers  leaving  a   ganglion  is  greater   than   the  number  of  fibers 
entering  it.    This  is  due  to  the  fact  that  the  preganglionic  fibers  divide. 

The  spheno-palatine  ganglion  of  the  fifth  cranial  nerve  obtains 
its  preganglionic  fibers  from  the  facial.  Its  nerve-cells  send  post- 
gansiionic  fibers  to  the  Ijlood-vessels  and  glands  of  the  mouth  and 
nose.  Stimulation  of  this  ganglion  dilates  the  blood-vessels  and  aug- 
ments secretion. 

The  otic  ganglion  of  the  fifth  cranial  nerve  obtains  its  pre- 
ganglionic fibers  from  the  ninth  nerve  by  the  pathway  of  Jacobson"s 
nerve  and  the  small  petrosal.  The  postganglionic  fibers  run  in  the 
auriculo-temporal  of  the  fifth,  to  increase  the  secretion  of  the  parotid 
gland  and  to  dilate  the  blood-vessels. 

The  submaxillary  and  the  sublingual  ganglia  acquire  their  pre- 
ganglionic fibers  from  the  chorda  tympani  of  tlie  facial.  Their  post- 
(^anglionic  fibers  dilate  the  blood-vessels  and  increase  the  secretions 
of  these  glands. 


642  PHYSIOLOGY. 

As  to  the  bulbar  origin,  tlic  autonomic  efferent  fibers  of  the 
vagus  end  in  the  cardiac  ganglia,  from  which  postganglionic  fibers 
run  to  the  cardiac  muscle.  In  its  course  the  vagus  meets  small 
groups  of  nerve-cells  in  the  lungs,  the  external  wall  of  the  ceso- 
pliagus,  and  the  stomach. 

The  vagus  sends  many  fibers  to  the  (enteric  nervous  system) 
Meissner-Auerbach  ganglia  in  the  stomach,  furnishing  secretory 
nerves  to  the  stomach  and  pancreas;  and  the  number  of  its  fibers 
in  its  downward  course  to  the  intestine  diminish,  and  are  completely 
absent  in  the  descending  colon.  The  Ijulbar  autonomic  system 
innervates  the  upper  part  of  the  digestive  tract,  from  the  mouth  to 


Mau*^  f\ 3r  ^^^^^^^''^ ^'^^onointc 


SipnpcJhetiC 


Sacral /lutoruiTm^ 


Fig.  289. — Diagram  of  the  Main  Distribution  of  the  Bulbar  and  Sacral 
Autonomic  Fibers.      (Langley.  ) 

The  bulbar  fibers  supply  the  anterior  end  of  alimentary  canal  and  the  sali- 
vary glands.  The  sacral  fibers  supply  the  posterior  end  of  the  alimentary  canal 
and  the  external  generative  organs.  The  sympathetic  supplies  the  whole  tract 
and  also  the  skin  and  the  internal  generative  organs  which  receive  no  involun- 
tary fibers  from  any  other  source. 

the  descending  colon,  and  the  cavities  and  organs  in  connection,  as 
the  salivary  glands,  the  lungs,  the  liver,  and  the  pancreas.  The 
sacral  a,utonomic  nerves  innervate  the  lower  part  of  the  digestive 
tract,  the  descending  colon,  anus,  bladder,  and,  by  their  nervi 
erigentes,  the  external  genitals.  The  sphincter  of  the  iris  and 
ciliary  muscle  receives  no  fibers  from  the  spinal  thoracic  sympathetic, 
but  only  cranial  autonomic  nerves.  The  bul])ar  and  sacral  autonomic 
systems  are  independent  of  the  spinal  thoracic  sympathetic  system 
as  regards  development,  and  are  not  a  part  of  the  spinal  sympathetic 
system. 

A  long  series  of  fibers  arise  from  the  thoracic  and  upper  lumbar 
spinal  cord.     These  are  the  fibers  of  the  sympathetic  nervous  system. 


ANATOMY    AM)    I'HYSIOLOGY    OF    ^.ERVOUS    SYSTEM. 


G43 


Fig.  290. — Diagram  of  tiie  Great  Sympathetic,  Representing  its 
Visceral    Distribution.      (MoRAT. ) 

On  the  right,  medulla  oblongata,  spinal  cord,  and  roots.  In  the  middle,  ver- 
tebral chain  and  ganglia;  on  the  left,  second  chain  (prevertebral)  formed  by 
the  pneumogastric  nerve  and  the  mesenteric  nerves,  solar  ple.xus  and  hypogastric 
plexus.  On  the  extreme  left,  terminal  ganglia  and  plexuses  of  the  viscera. 
The  break  between  the  peripheral  and  deep  neurons  is  effected  either  in  the 
catenary,  terminal  or  intermediate  ganglia.  Symmetrical  with  regard  to  a  plane, 
xy,  which  intersects  the  thorax.  Principal  condensed  origins  in  the  thoracic 
region.  Supplementary  origins  arising  from  the  medulla  oblongata  (nerve  of 
Wrisberg  and  pneumogastric)  and  from  the  sacral  spinal  cord   (erector  nerves). 


644 


PHYSIOLOCtY. 


& 


II 


as 


Fig.  291. — Diagram  of  tlie  Great  Sympathetic,  Representing  its  Cutane- 
ous Distribution  and  its  Two  Orders  of   Fibers  of  Projection. 

On   the   right   of  the   diagram,   the   medulla  oblongata,   the   spinal   cord   and 
their  roots;     on  the  left  the  cutaneous  nerves,   containing  those  roots    (chosen 


ANATOMY   AND    PHYSIOLOGY    OF    JMERVOUS    SYSTEM. 


645 


The  chief  difference  between  the  sympathetic  and  the  parasym- 
pathetic systems  is  that  the  former  sends  nerve-fibers  to  all  parts  of 
the  body,  whilst  the  latter  sends  fibers  only  to  certain  parts.  Accord- 
ing to  Langley,  when  a  tissue  has  a  double  innervation  the  effect  pro- 
duced by  one  set  of  fibers  is,  in  most  cases,  the  opposite  of  the  main 
effect  produced  by  the  other  set  of  fibers.  Thus,  if  one  set  causes 
mainly  contraction,  the  other  causes  mainly  inhibition. 


PosfRoot  (cy^^ 
Oan^/ion.  V  '  ~J 


Fig.  292. — An  Afferent  Sympathetic   Fiber. 

Adrenalin,  when  injected,  produces  all  the  effects  seen  from 
stimulating  the  sympathetic  nerves,  but  does  not  produce  any  of  the 
effect  characteristic  of  stimulation  of  the  parasympathetic  nerves. 
Hence  it  is  a  test-agent  for  the  presence  of  sympathetic  fibers. 

The  pilomotor  nerves   come   from   the   cord,   from   the   fourth 


on  account  of  their  more  regularly  metameric  distribution) ;  in  the  middle  the 
ganglia  of  the  sympathetic  chain.  These  ganglia  give  off  branches  of  distribu- 
tion in  which  join  the  cutaneous  nerve  belonging  to  the  same  metamere  as  the 
branch  itself  and  the  ganglion  which  has  given  it  off.  On  the  other  hand,  these 
ganglia  receive  branches  of  medullary  origin  which  arise  from  segments  of  the 
spinal  cord  situated  either  higher  or  lower  than  the  corresponding  metamere. 
Spinal  origins  condensed  in  the  thoracic  region,  supplementary  regions  in  the 
medulla  oblongata  and  the  sacral  spinal  cord.  Symmetrical  arrangement  with 
regard  to  a  plane  (.r;/)  cutting  across  the  middle  of  the  thoracic  region. 


64G 


PHYSIOLOCY. 


tlioracic  to  tlic  third  Iiinil)ar  nerves,  in  the  eat,  and  are  distributed 
to  the  unstri])e(l  niusele  about  the  roots  of  tlie  hairs  and  cause  erec- 
tion of  them.  The  condition  of  the  skin  known  as  "goose-skin"  is 
due  to  tliese  nerves. 

Syni])athetic    fil)ers,    according    to    their    distribution,    can    be 
divided  into  cutaneous  or  somatic,  and  visceral  or  splanchnic. 


/I  rteriole  of  He.<^cL 


nerve  and 
cfiionic  fiber 


ghoiiic  fiber 
etic  Ga  notion 


fhehc  Ganglion. 


janolioTLic 


-^ 


fi rteriole 


Fig.  293. — Efferent  Sympathetic  Filler. 


Afferent  fibers  take  their  origin  in  the  ganglion  of  the  posterior 
root.  The  efferent  fibers  arise  from  the  interniedio-lateral  column 
of  cells,  and  pass  out  by  the  anterior  roots. 

The  efferent  fibers  of  the  head  and  neck  come  from  the  upper 
five  dorsal  nerves,  and  run  up  in  the  cervical  sympathetic  to  the 
superior  cervical  ganglion,  where  they  have  their  cell  station.  From 
this  ganglion  the  following  fibers  arise: — 

1.  Vasocontrictors. 


ANATOMY    AND    PHYSIOLOGY    OF   NERVOUS    SYSTEM.         647 

2.  Pupillo-dilator  to  the  Gasserian  ganglion,  in  the  ophthahnic 
branch  and  long  ciliary  nerves  to  dilator  fibers  of  the  iris. 

3.  Motor  to  Miiller's  smooth  muscle  of  the  orbit  and  Tenon's 
capsule. 

4.  Secretory  to  sweat-glands. 

If  you  irritate  the  cervical  portion  of  the  sympathetic,  the  eye- 
ball is  projected  by  a  contraction  of  the  smooth,  muscular  fibers  of 
the  capsule  of  Tenon;  the  pupil  dilated.  The  recti  muscles  push 
the  eyeball  inward.  The  vasomotor  nerves,  constrictors,  and  dila- 
tors are  in  the  cervical  sympathetic,  and  when  it  is  irritated  the 
blood-vessels  of  the  ear,  conjunctiva,  iris,  tongue,  epiglottis,  and 
palate  are  contracted,  whilst  we  have  a  dilatation  of  the  vessels  of  the 
retina,  lips,  gums,  and  nasal  mucous  membrane. 

The  cervical  sympathetic  also  acts  upon  the  circulation  of  the 
brain  and  that  of  the  thyroid  gland. 

Thorax. — The  fibers  of  the  thoracic  organs  arise  from  the  five 
upper  dorsal  nerves,  go  out  through  the  first  thoracic  ganglion,  then 
go  through  the  annulus  of  Vieussens  to  the  inferior  cervical  ganglion. 
and  pass  to  the  heart  and  lungs,  as  the  cardio-accelerator  and  the 
vasoconstrictors   of  the  lungs. 

Abdomen. — These  fibers  come  off  from  the  lower  six  dorsal  and 
upper  three  lum])ar  nerves.  The  great  splanchnic  nerve  is  formed 
by  branches  from  the  fifth  to  the  tenth  thoracic  ganglia,  and  termi- 
nates in  the  semilunar  ganglion  of  the  solar  plexus  and  in  the 
superior  mesenteric  plexus. 

The  lesser  splanchnic  is  formed  by  filaments  from  the  tenth  to 
eleventh  thoracic  ganglia,  and  goes  to  the  solar  and  renal  plexus. 
The  splanchnic  nerves  are  the  greatest  vasoconstrictor  nerves  in  the 
body,  and  contain  inhibitory  fibers  of  the  small  intestines.  They  also 
contain  motor  fibers  to  the  intestines. 

Pelvis. — The  fibers  for  the  pelvis  emerge  from  the  cord  by  the 
lower  dorsal  and  upper  four  lumbar  nerves,  and  have  their  cell-sta- 
tion in  the  inferior  mesenteric  ganglia,  from  which  they  run  in  the 
hypogastric  nerves  to  the  pelvic  ganglia.  They  contain  vasoconstric- 
tors, inhibit  the  colon,  give  motor-power  to  the  bladder,  uterus,  and 
vagina. 

The  mesenteric  nerves  go  to  the  superior  mesenteric  ganglion, 
and  then  to  the  hypogastric  plexus.  The  coeliac,  the  superior  mesen- 
teric, and  the  hypogastric  prevertebral  ganglia  are  united  amongst 
themselves  by  connections  parallel  to  the  sympathetic  chain.  These 
ganglia  form  in  some  sort  a  second  chain  anterior  to  that  which  fol- 


648  PHYSIOLOGY. 

lows  the  lumbar  vertebral  chain.  This  prevertebral  chain  receives 
elements  of  reinforcement  by  two  remarkable  paths.  The  first  is 
that  of  the  vagus,  which  carries  bulbar  influences.  The  second  is 
that  path  formed  by  the  nervi  erigentes,  which  come  off  from  the 
second  and  third  sacral  nerves  and,  like  the  bulbar  and  midbrain 
nerves,  do  not  enter  the  sympathetic  ganglia,  but  go  to  the  hypo- 
gastric plexus  near  the  bladder,  where  the  fibers  have  their  cell-sta- 
tion. They  are  vasodilator  nerves  to  the  pelvic  organs,  inhibit  the 
retractor  penis,  and  are  motor  to  the  bladder, 'colon,  and  rectum. 

In  the  heart  and  lungs,  the  vagus  is  inhibitory  and  the  sympa- 
thetic is  accelerator.  For  the  gastric  and  intestinal  muscles  the 
pneumogastric  mainly  augments,  whilst  the  sympathetic  chiefly 
inhibits. 

Arm. — These  fibers  come  out  by  the  fourth  to  tenth  dorsal 
nerves,  and  send  fibers  to  the  stellate  ganglion  and  from  there  pass 
into  the  spinal  nerves,  and  go  to  the  blood-vessels,  sweat-glands,  and 
pilomotor  muscles  of  the  skin  and  limb. 

Leg. — These  fibers  take  origin  from  the  eleventh  dorsal  to  third 
lumbar  nerves,  and  come  out  of  the  last  two  lumbar  and  first  two 
sacral  ganglia  and  go  to  the  leg  in  the  spinal  nerves,  to  supply  the 
blood-vessels  and  pilomotor  muscles  and  secretory  nerves. 

Langley  regards  the  nerve-cells  of  Auerbach  and  Meissner's 
plexus  of  the  intestinal  tract  (the  enteric  nervous  system)  as  differ- 
ent, both  from  the  sympathetic  and  parasympathetic  system.  He 
does  not  know  if  they  are  connected  with  the  sympathetic  or  para- 
sympathetic, but  doubts  it.  Magnus  has  shown  that  the  nerve-cells 
of  Auerbach's  plexus  are  reflex  centers  for  the  rhythmic  contractions 
of  the  intestines.  Langley  believes  that  in  the  intestine  there  are 
two  sets  of  nerve-cells,  one  motor,  the  other  inhibitory,  both  acting 
on  the  muscular  tissue,  the  state  of  the  muscle  depending  on  the 
balance  of  the  two  forces. 

Afferent  Fibers. — They  have  their  cell-station  in  the  ganglion  of 
the  posterior  root.  They  enter  the  cord  largely  by  the  white  rami. 
ISTormally,  stimulation  of  their  peripheral  endings  does  not  lead  to 
modifications  of  consciousness,  and  is  therefore  not  accompanied  by 
pain.     In  abnormal  conditions  painful  sensations  are  produced. 

Head  has  shown  that  the  sensation  of  pain  from  visceral  dis- 
eases is  referred  to  certain  points  on  the  surface  of  the  body.  Thus, 
intestinal  trouble  causes  pain  in  the  skin  of  the  back,  abdomen,  and 
loins.  In  stomach  troubles,  the  pain  is  referred  to  the  ensiform 
cartilage;   in  disease  of  the  heart,  to  the  scapular  region.     Here  the 


ANATOMY   AND   PHYSIOLOGY    OF   NERVOUS   SYSTEM.         649 

pain  in  the  skin  is  due  to  the  segment  of  the  spinal  cord  from  which 
the  organ  concerned  receives  its  sensory  fibers,  there  being  a  spread 
of  it  through  the  nerve-centers,  and  tlius  causing  an  error  in  its 
localization. 

Blows  on  the  solar  plexus  reflexly  cause  arrest  of  the  heart. 
The  splanchnics  also  have  sensory  nerves  for  the  intestine,  and  in 
intestinal  cram})  may  give  rise  to  extremely  painful  sensations.  In 
the  colic  due  to  lead-poisoning,  we  have  an  affection  of  the  sympa- 
thetic ganglia. 

Reflex  Action  of  the  Sympathetic  Ganglia. — Snkownin  has  found 
that  when  in  the  cat  the  nervous  connections  of  the  inferior 
mesenteric  ganglion  are  divided,  with  the  exception  of  the  hypogas- 
tric nerves,  and  when  the  central  cut  end  of  one  hypogastric  is  stim- 
ulated, contraction  of  the  bladder  ensues  on  the  opposite  side. 
According  to  Langley,  this  is  not  a  true  reflex,  but  an  axon  reflex. 


CHAPTER  XV. 

SPECIAL  SENSES. 

TACTILE  SENSE. 

TjiK  organs  of  special  sense  constitute  the  periplicral  portion  of 
the  centripetal  part  of  the  nervous  system.  The  nervous  system  is 
open  to  receive  the  impressions  from  the  external  world  according 
to  the  nature  of  the  different  agents  which  must  impress  the  organs 
of  the  special  senses. 

The  various  kinds  of  sense-organs  have  each  a  different  con- 
struction. They  are  always  adapted  to  receive  an  impression  of  a 
given  agent.  Thus,  the  eye  is  an  organ  that  is  particularly  adapted 
to  receive  impressions  from  rays  of  light;  the  ear  receives  sound- 
waves;   the  skin  is  responsive  to  touch,  etc. 

Man  is  endowed  with  five  senses.  That  is.  he  possesses  five  kinds 
of  organs  which  are  destined  to  give  him  notice  of  the  impressions 
upon  his  nervous  system  from  five  different  agents.  To  these  agents 
man  has  assigned  special  names  which  recall  their  relations  to  the 
organs  of  sense,  and  without  which  they  could  not  he  conceived  of. 
These  agents,  with  the  corresponding  organs  of  sense,  are  (1)  contact, 
which  is  perceived  through  the  sense  of  touch,  whose  highest  devel- 
opment is  in  the  skin;  (2)  taste,  a  modification  of  touch  is  perceived 
^through  the  sense  of  taste  emhodied  in  the  tongue;  (3)  odor  is  recog- 
nized through  the  sense  of  smell  as  located  in  the  nose;  (4)  sound- 
waves are  made  known  to  the  economy  through  the  sense  of  hearing, 
whose  peripheral  organ  is  the  ear;  and  (5)  light  is  perceived  through 
sif/ht  hy  reason  of  tlie  response  produced  in  the  eye  from  the  excita- 
tion of  rays  of  light. 

Miiller's  law  of  the  specific  energy  of  sensory  nerves  is  that  irri- 
tation of  the  nerves  of  special  sense  always  causes  sensations  of  the 
same  kind.  An  induction  current  upon  the  skin  will  produce  un- 
pleasant tactile  sensations.  Upon  the  eye  it  provokes  luminous  sensa- 
tions, upon  the  ear,  noise  sensations,  and  upon  the  tongue  there  is  pro- 
duced a  sensation  of  taste.  Yet  in  each  case  the  stimulus  is  always 
the  same. 

In  order  that  the  impressions  caused  by  the  external  excitants 
may  he  able  to  reach  the  consciousness  of  the  individual,  it  becomes 
necessary  that  each  organ  of  sense  be  furnished  with  centripetal 
(650) 


TACTILE  SENSE.  651 

nerves.  These  are  in  direct  anatomical  relation  with  the  central 
nervous  system.  By  means  of  these  nerves  the  cortical  portion  of  the 
cerebrum,  endowed  with  consciousness,  perceives  the  impressions  com- 
ing from  the  external  world.  These  are  the  so-called  special,  external 
and  objective  sensations. 

Among  the  parts  furnished  with  nerves  of  general  sensibility  are 
the  mucous  membrane  of  the  digestive,  respiratory ,  and  genito-urinary 
tracts,  and  the  skeletal  muscles.  In  the  digestive  tract,  the  mouth, 
pharynx,  and  anus  are  endowed  with  tactile  nerves;  the  rest  of  the 
tract  is  furnished  with  nerves  of  general  sensibility.  The  mucous 
membrane  of  the  oesophagus  gives  us  the  sensation  of  thirst,  the 
gastric  mucous  membrane  the  sensation  of  hunger  and  satiety,  while 
the  rectal  membrane  notifies  the  individual  of  the  need  of  defecation. 

Pulmonary  tissue  in  itself  has  but  very  little  sensibility;  but  ab- 
normal irritations  cause  cough  and  painful  sensation.  The  pleura, 
when  invaded  by  disease,  produces  very  painful  sensations. 

The  genito-urinary  membrane,  besides  its  exquisite  tactile  sensi- 
bility, is  also  the  seat  of  general  sensibility  that  is  doubly  modified: 
in  the  need  of  urination  and  the  sexual  sense.  The  kidneys,  ureters, 
testes,  Fallopian  tubes,  and  the  uterus  are  endowed  only  with  nerves 
of  general  sensibility. 

The  slieletal  muscles  are  furnished  with  the  so-called  muscular 
sense. 

Muscular  Sense. — According  to  Dr.  Sherrington,  of  Liverpool, 
this  is  a  specific  sensation  obtained  from  specific  sense-organs  in 
muscles,  tendons,  joints,  and  all  the  accessory  organs  of  movement. 
In  the  muscles  of  the  skeleton  there  are  three  sets  of  sensory  organs: 
muscle-spindles,  tendon-organs,  and  Pacini  corpuscles. 

Muscle-spindles,  or  neuromuscular  spindles,  are  long,  narrow 
bodies,  with  a  thick  sheath  of  connective  tissue  enclosing  fine  striped 
muscular  fibers.  Sensory,  medullated  nerve-fibers  enter  the  spindle, 
dividing  into  branches,  and  losing  their  medulla  fonn  endings  around 
and  between  the  muscular  fibers.  The  perception  of  muscular  sense 
may  be  grouped  into:  (1)  those  of  posture;  (2)  those  of  passive 
movement;  (3)  those  of  active  movement;  and  (4)  those  of  resist- 
ance to  movement. 

To  the  organs  of  muscular  sense  is  largely  traceable  a  local 
feeling  of  fatigue. 

The  nerves  of  muscle  are  competent  to  ]n-oduce  pain ;  this  is 
proved  by  the  pain  of  muscular  cramp. 

A  proof  of  muscular  sense  is  the  employment  of  enough  force 


652 


pnYSi()i.()(iv. 


to  overcome  resistance.  Consciousness  is  a  large  factor  in  this  last 
function,  for  by  it  the  individual  Judges  the  amount  of  resistance. 
He  then  vohintarily  regulates  the  amount  of  muscular  effort. 

It  is  by  the  sum  of  all  the  sensations  from  the  nerves  of  general 
sensibility,  as  well  as  the  sensation  produced  by  muscular  movement, 
that  individuals  feel  that  they  exist.  With  these  data  the  individual 
recognizes  the  state  of  different  parts  of  his  body,  whether  in  repose 
or  activitv. 


^-i  ^. mn 


1' ig.   2SJ4. — C  loss-sectiun  of   JveuiotciKlinous    Nerve   Eiid-oigHn   of   Rabbit 
from  Tissue  Stained  in  Methylene  Blue.      (Huber  and  Dewitt.  ) 

m.  Muscle  fibers,     i.  Tendon,     r,  Capsule  of  neuro-tendinous  end-organ. 
mn,   Medullated  nerve  fiber. 


Laws  of  Sensation. — Special  sensations  are  subject  to  the  fol- 
lowing laws : — 

1.  For  every  nerve  of  sense  there  is  a  nominal  degree  or  limit  of 
stimulus  which  gives  no  sensation  whatever.  There  is  also  a  max- 
imum degree  beyond  which  an  increase  of  the  intensity  of  the  stim- 
ulus brings  on  pain  or  an  unpleasant  sensation. 


TACTILE  SENSE.  553 

2.  The  minimum  limit  varies  for  the  separate  sensations,  or. 
rather,  the  single  specific  agents.  Thus,  the  minimum  for  excitation 
of  touch  is  a  pressure  of  0.003  milligrams;  for  temperature,  Vg"  C; 
for  sensation  of  movement,  a  shortening  to  the  extent  of  0.044  milli- 
meters of  the  internal  rectus  of  the  eye ;  for  hearing,  the  noise  made 
by  a  hall  of  pith  one  milligram  in  weight  falling  one  millimeter  in 
height  upon  a  glass  plate  heard  at  a  distance  of  ninety-one  milli- 
meters from  the  ear;  for  sight,  an  intensity  of  light  ahout  three 
hundred  times  feehler  than  that  of  the  full  moon. 

3.  The  intensity  of  the  sensation  is  proportional  to  the  intensity 
of  the  stimulus  and  the  degree  of  irritability  of  the  nerve  at  the 
moment  of  excitation.  As  the  strength  of  the  stimulus  increases,  so 
do  the  sensations.  But  the  sensations  increase  equally  when  the 
strength  of  the  stimulus  increases  in  relative  proportions.  Thus, 
small  noises  will  he  distinguished  in  the  silence,  not  in  the  midst  of 
loud  noises ;  a  sliglit  difference  will  be  noticed  between  small  weights, 
not  between  heavy  ones.  A  burning  candle  in  the  daytime  makes 
little  impression. 

4.  Sensations  do  not  increase  in  the  same  proportion  as  the 
stimulus.  If  the  stimulus  increases  in  geometrical  progression,  then 
the  sensation  increases  in  simple  arithmetical  progression.  Eather, 
it  increases  as  the  logarithm  of  the  stren.gth  of  the  stimulus.  (This  is 
Fechner's  psycho-physical  law.) 

5.  For  the  single,  specific  sense  apparatuses,  whenever  a  stimulus 
takes  place,  whether  at  the  peripheral  terminations  of  a  nerve  or  in 
its  course,  or  at  its  central  point,  the  individual  always  localizes  with 
his  perception  the  stimulus  at  the  place  where  the  normal  stimulus 
operates.  That  is,  for  sight  and  hearing  he  refers  it  to  space ;  for  the 
nerves  of  taste,  smell,  or  touch,  he  refers  it  to  the  peripheral  regions 
of  his  body,  even  if  these  be  lacking.  Thus,  in  an  amputated  leg,  pain 
in  the  stump  is  referred  ■  to  the  toes.  This  is  the  law  of  eccentric 
projection  of  sensation. 

Touch. 

The  organ  of  touch  is  represented  by  the  skin  and  mucous  mem- 
branes in  proximity  to  the  natural  orifices  of  the  body. 

The  skin,  or  common  integument,  is  composed  of  the  following 
layers:  (1)  the  epidermis;  (2)  the  corium,  or  cutis  vera,  with  its 
papilla;    and  (3)  the  subcutaneous  tissue  with  the  adipose  tissue. 

1.  The  Epidermis  belongs  to  the  tissues  which  are  composed  of 
simple  cells  imited  to  each  otlu^r  by  cement-substance.  It  in  itself 
consists  of  several  1  avers. 


654 


PHYSIOLOGY. 


Fig.  295. — Histolog}^  of  the  Skin  and  the  Epidernioidal  Structures. 

(Landois.  ) 

I,  Transverse  section  through  the  skin,  with  hair  and  sebaceous  glands  (7'), 
cerium  and  epidermis  are  shown  in  reduced  size.  1,  External,  2,  Internal 
fibrous  layer  of  the  hair-follicle.  3,  Cuticula  of  the  hair-follicle.  4,  External 
root-sheath.  5,  Henle's  layer  of  the  inner  root-sheath.  6,  Huxley's  layer  of  the 
Inner  root-sheath,  p,  Hair-root  attached  to  the  vascular  hair-papilla.  .4,,  Ar- 
rector  pill  muscle.  C,  Corium.  a,  Subcutaneous  fatty  tissue.  6,  Horny  layer. 
il,  Malpighian  mucous  layer  of  the  epidermis,  g.  Vessels  of  the  cutaneous 
papilla.  V,  Lymphatics  of  the  cutaneous  papillae,  h.  Horny  substance,  i. 
Medullary  canal,  fr,  Epidermis  of  the  hair.  A',  Sudoriferous  gland.  E.  Epi- 
dermal scales  from  the  horny  layer,  viewed  partly  from  the  side,  partly  from 
the  surface.  R,  Prickle-cells  from  the  Malpighian  layer,  n.  Superficial,  deep 
nail-cells.  H,  Hair,  more  highly  magnified,  e.  Epidermis,  f.  Medullary  canal 
with  medullary  cells,  f,  f,  Fiber  cells  of  the  hair-substance,  cc.  Cells  of  Hux- 
ley's layer.  1,  Cells  of  Henle's  layer.  S,  Transverse  section  through  a  sudo- 
riferous gland  of  the  axillary  cavity,  a.  Adjacent  unstriated  muscular  fibers. 
/,  Cells  of  a  sebaceous  gland,  in  part  with  fatty  contents. 


TACTILE  SENSE.  655 

(a)  Stratum  Corneum. — This  is  the  superficial  horny  layer  and 
consists  of  several  layers  of  horny  scales,  without  any  nuclei.  The 
layers  are  separated  from  one  another  by  narrow  clefts  containing  air. 
They  are  in  a  process  of  desquamation.  The  variable  thickness  of 
the  epidermis  is  chiefly  dependent  upon  the  thickness  of  this  outer 
layer.  The  stratum  corneum  is  of  greater  thickness  on  the  palm  of 
the  hand  and  fingers,  and  sole  of  the  foot. 

(b)  The  stratum  lucidum  is  clear  and  transparent  and  consist? 
of  a  few  layers  of  clear  cells  which  contain  l)ut  the  remains  of  nuclei. 

(c)  Stratum  Granulosum. — Under  this  is  the  (d)  rete  muco- 
sum,  or  rete  Malpighii.  This  layer  consists  of  strata  of  nucleated, 
protoplasmic,  epithelial  cells.  In  the  colored  races  these  contain 
pigment.  Among  the  fair  races  this  layer  of  th*e  skin  of  the  scrotum 
and  anus  contains  pigment-granules.  The  deeper  cells  are  more  or 
less  polyhedral,  while  the  deepest  ones  are  columnar.  These  last  are 
placed  vertically  upon  the  papilla?  and  are  provided  with  spherical 
nuclei.  Granidar  leucocytes  or  wandering  cells  are  occasionally  found 
between  these  cells. 

The  superficial  layers  of  the  epidermis  are  continually  being 
thrown  off,  while  new  cells  are  just  as  rapidly  being  formed  in  the 
deep  layers.  Within  them  there  occurs  a  proliferation  of  the  cells  of 
the  rete  Malpighii.  Many  of  the  cells  exhibit  the  changes  of  karyo- 
kinesis.  No  pigment  is  formed  within  the  epidermis  itself.  But  in 
brunettes  and  colored  races  pigment  granules  of  melanin  exist  within 
the  cells  of  the  lowermost  layers  of  the  stratum  Malpighii.  The 
pigment-granules  owe  their  presence  here  to  their  having  been  car- 
ried thither  by  leucocytes  from  the  subcutaneous  tissue.  This  ex- 
plains how  a  piece  of  white  skin  transplanted  to  a  colored  person 
becomes  black. 

2.  The  Corium,  or  cutis  vera,  is  a  dense  network  of  fibrous  con- 
nective tissue  admixed  with  elastic  fibers.  Its  entire  surface  is  studded 
with  numerous  papiUo',  the  largest  of  which  are  upon  the  volar  surface 
of  the  hand  and  foot.  The  majority  of  the  papillae  contain  a  looped 
capillary.  In  some  regions  of  the  surface  of  the  body  they  contain 
touch-corpuscles.  The  papilla^  are  arranged  in  groups  whose  disposi- 
tion varies  in  the  several  parts  of  the  body. 

The  lowermost  connective-tissue  layers  of  the  corium  gradually 
merge  into  the  subcutan-eous  tissue.  Its  arrangement  is  such  as  to 
leave  spaces  which  contain,  for  the  most  part,  cells  of  fat.  The  sub- 
cutaneous connective  tissue,  composed  of  ordinary  connective  tissue, 
is  soft,  and  is  rich  in  adipose  cells,  vessels,  nerves,  and  lymphatics. 


(;;")()  rilYSiOLOGY. 

Tactile  Corpuscles. — The  student  well  knows  that  in  the  epithe- 
lium of  the  skill  and  mucous  membranes  the  nerves  of  common  sen- 
sation are  arranged,  for  the;  most  ])art,  in  nelworlhS  of  fibrillar.  In 
addition  to  these  there  are  otiiei-  special  terminal  organs  of  sensory 
nerves.  These  are  variously  known  as  tactile  corpuscles.  These  are 
concerned  in  the  ])erception  of  some  special  quality  or  (juantity  of 
sensory  impulses.  They  have  their  site,  not  in  tlie  surface  of  the 
epidermis,  but  deeper  within  the  tissues.  The  principal  ones  among 
them  are  the  corpuscles  of  Pacini,  the  end-bulbs  of  Kruuse,  the  cor- 
puscles of  Meissner,  and  the  corpuscles  of  Merkel. 

The  tactile  corpuscles  of  Meissner  in  the  papilla  of  the  cutis 
vera  are  oval  bod  it's  V,„  of  an  inch  in  length  and  nearly  the  same 
width.  These  are  tire  corpuscles  of  the  palm  of  the  hand  and  sole 
of  the  foot.     One  or  two  medullated  nerve-fibers  are  spirally  twisted 


Fig.  29G. — Cutaneous  Papillae  Deprived  of  Their  Epidermis  and  the 
Vessels  Injected.      (Landois.) 

a,  a,  a,  Tactile  papUlas,   eacli  containing  a  Meissner  corpuscle. 

around  it,  and  near  the  top  of  the  corpuscles  the  nerves  lose  their 
white  substance  and  the  axis-cylinders  end  in  flat  bodies  penetrating 
the  surface  of  the  corpuscle.  The  corpuscle  is  composed  of  flattened 
cells,  which  give  it  a  striated  appearance.  These  corpuscles  are  built 
up  of  a  great  number  of  tactile  discs  and  of  tactile  cells.  There  are 
about  twenty  tactile  corpuscles  to  a  square  millimeter  of  the  skin. 

The  Pacinian  or  Vater's  corpuscles  are  attached  in  greatest  num- 
ber along  the  digital  nerves  of  the  fingers  and  toes  and  occasionally 
on  other  nerves.  These  bodies  are  oval  or  pyriform,  about  one- 
eighth  of  an  inch  in  length  and  one-twelfth  of  an  inch  in  thickness. 
They  have  a  pearly  luster  and  consist  of  a  series  of  capsules  or  con- 
centric layers  of  fibrous  tissue,  with  here  and  there  a  nucleus.  The 
outer  capsules  are  separated  more  widely  than  the  inner  ones  and 
the  interspaces  are  tilled  with  a  colorless  liquid.  Each  corpuscle  is 
attached  to  a  nerve  by  a  pedicle  of  fibrous  tissue  through  which 


TACTILE  SENSE.  557 

extends  a  single  nerve-fiber,  wliicli,  jDcnetrating  the  series  of  capsules, 
terminates  by  sending  its  neuraxon  into  the  central  cavity  of  the  cor- 
puscle, at  the  top  of  which  it  ends  in  a  simple  extremity.  Each  cor- 
puscle is  covered  with  forty  or  fifty  capsular  layers. 

Krause's  End-bulbs. — The  tactile  corpuscles  of  Krause  are  elon- 
gated, oval  bodies,  into  one  end  of  which  a  nerve-fiber  penetrates. 
Externally  they  have  a  covering  of  connective  tissue,  a  continuation 
of  the  perineurium,  and  an  internal  knob  of  granular  matter  dis- 
posed in  concentric  layers  with  a  few  nuclei.  In  the  center  of  this 
knob  is  found  the  axis-cylinder  which  runs  through  it  like  a  ribbon 
to  the  upper  pole  and  then  ends  in  a  slight  thickening.     These  bulbs 


Fig.  297. — Vater  Paciiiian  e  uipu.^Llc  lioiu  the  Mesentery  of  the  Cat, 
Fixed  in  a  Platinvim  Chlorid-osmic  Acid  Solution.     X  45.      (Sobotta.) 

The  figure  gives  a  general  view  of  the  corpuscle  and  not  a  cross-section. 
a.  Axis  cylinder  in  the  core,  ik.  Core,  mn,  Medullated  nerve-fibers  entering 
the  corpuscle. 

are  found  in  the  basement  membrane  of  certain  mucous  membranes, 
as  in  the  corneal  conjunctiva,  in  the  mucous  membrane  of  the  mouth, 
in  the  clitoris,  and  in  the  glans  penis.  They  are  also  to  be  found  in 
the  skin. 

Corpuscles  of  Grandry  or  of  Merkel  consist  of  two  or  more  flat- 
tened cells,  each  larger  than  a  simple  tactile  cell.  Each  cell  is 
nucleated,  and  the  nerve-fiber,  before  entering  the  corpuscle,  loses 
its  white  sheath,  and  the  axis-cylinder  ends  as  a  flat  disc  lying 
between  the  two  tactile  cells.  These  tactile  cells  are  piled  one 
upon  the  other  so  as  to  form  a  heap  of  cells.  They  are  found  chiefly 
in  the  lioak  and  tongue  of  the  duck  and  in  the  epidemi  of  man. 

Other  Modes  of  Ending. — In  addition  to  sensory  nerves  ending 
by  special  structures  as  those  Just  described,  there  are  some  which 

42 


658 


PHYSIOLOGY. 


do  not  possess  such  elaborate  apparatus.  In  the  case  of  many  nerves, 
the  axis-cylinder  splits  up  into  fibrils  which  are  arranged  in  the  form 
of  a  network.  From  this  somewhat  deeply  placed  network  very  fine 
llhrils  or  fibrillar  are  given  off  to  terminate  in  the  tissues  to  be  sup- 
plied. The  fibrilla}  have  their  terminus  in  free  ends  lying  between 
the  epithelial  cells.  In  many  cases  the  free  ends  are  seen  to  be  pro- 
vided with  small  enlargements.  These  latter  are  known  as  tactile 
cells. 

Knowledge  Gained. — By  the  sense  of  touch  one  feels  the  con- 
tact of  bodies  and  their  temperature,  whether  these  bodies  be  solid, 
liquid,  or  gaseous.  This  special  sense  also  defines  at  the  same  time 
the  locality  of  the  impression  made  by  the  external  agent.     The  judg- 


Fig.  298. — Kiause's  Corpuselo.     (Hedon.) 
a,  Nerve  fiber,     b.  Corpuscle. 

ment  of  locality  is  not,  however,  free  from  error.  It  is  really  exact 
for  but  a  few  points;  that  is,  wherever  the  touch  is  delicate.  On 
the  other  parts  of  the  skin  the  individual  never  exactly  divines  the 
point  pressed  upon ;  so  that  he  makes  mistakes  of  millimeters,  centi- 
meters, and  even  decimeters. 

In  sensory  nerve-trunks  there  exist  different  kinds  of  nerve- 
fibers;  some  administer  to  painful  impressions  and  others  to  tactile 
impressions.  Sensations  of  temperature,  sensations  of  pressure,  and 
of  muscular  sense  belong  to  the   latter  group. 

There  are,  then,  four  sense  qualities  in  skin-sensations:  sensa- 
tions of  pain,  temperature,  pressure,  and  muscle-sense,  and  each  one 
has  its  own  nerve-fiber. 

Sense  Spots. — The  surface  of  the  skin  is  found  by  experimenta- 
tion to  be  composed  of  very  small  sensorial  areas.     Between  these 


TACTILE  SENSE.  g59 

areas  are  found  little  fields  which  are  insensitive  and  which  are  rela- 
tively much  larger  than  the  sensitive  areas,  or  "spots."  It  has  been 
demonstrated  that  each  "spot"  has  its  own  specific  function  to  per- 
form, whether  that  be  touch,  cold,  warmth,  or  pain.  Each  little 
sensitive  area  no  doubt  marks  the  site  of  single  or  groups  of  sensory 
corpuscles,  end-organs,  or  bulbs,  of  the  terminations  of  various 
nerves.  Where  the  nerves  terminate,  there  are  the  sense-spots  rep- 
resented upon  the  skin's  surface. 

Some  one  has  very  aptly  likened  the  skin  with  its  sense-spots 
to  a  pond  upon  whose  surface,  as  well  as  just  below  the  same,  are 
seen  lily  leaves  floating.  The  leaves  represent  the  sense-spots.  A 
pebble  thrown  into  the  pond  may  strike  one  or  more  leaves,  depend- 

Tz 


Tsch 


Fig.   299. — Transverse   Section   of   Two   Grandry's   Corpuscles   from   the 
Tongue  of  a  Duck.     X  450.      (Sobotta.  ) 

One  of  the  corpuscles  shows  two,  and  the  other,  four  tactile  cells,  mn, 
MeduUated  nerve-fibers,  entering  the  corpuscle.  Tsch,  Tactile  discs.  Tz,  Tactile 
cells. 

ing  upon  how  close  together  they  are  growing.  The  pebble  repre- 
sents a  stimulus,  and  by  its  presence  temporarily  stirs  up  or  throws 
into  a  state  of  excitation  the  leaves  struck  as  well  as  some  of  those 
adjacent. 

Upon  the  skin's  surface  may  be  demonstrated  "touch-spots," 
"cold-spots,"  "warmth-spots,"  and  "pain-spots."  These  are  all  mixed 
up,  though  those  of  one  kind  may  be  more  strongly  in  evidence  in 
certain  areas.  As  a  rule,  "pain-spots"  are  found  to  be  the  most 
numerous;   "warmth-spots"  are  the  least  likely  to  be  found. 

Solids. — These  act  upon  the  sense  of  touch  either  by  pressure 
or  by  traction:  Pressure  may  be  from  zero  to  a  maximum  whose 
limit  is  the  disorganization  of  the  tissues.  Up  to  a  certain  minimum, 
which  depends  upon  the  sensibility  of  the  region,  the  application  of 
pressure  excites  no  sensation.  The  minimum  pressure  corresponds 
to  the  sensation  of  simple  contact ;   this  by  degrees  gives  way  to  the 


600  PHYSIOLOGY. 

sensation  of  pressure.  When  the  pressure  is  sufficiently  increased 
there  results  pain.  This  in  turn  disappears  when  the  pressure  is 
increased  to  disorganization  of  the  tissues. 

Pressure  varies  not  only  in  inicusily,  l)ut  in  extent.  No  mat- 
ter how  the  latter  may  be  limited,  the  pressui'e  always  affects  at 
least  more  than  one  peripheral  nerve-ending. 

When  tactile  sensations  are  very  light  and  succeed  one  another 
rapidly,  a  large  number  of  nerves  is  stimulated.  The  sensation  ex- 
cited is  a  peculiar  one :   that  of  ticMing. 

Traction  uj)on  the  hair  and  nails  determines  pain  much  more 
rapidly  than  does  pressure. 

Liquids. — Liquids  applied  at  the  temperature  of  the  skin  exer- 
cise a  uniform  pressure  upon  all  parts  of  the  cutaneous  surface 
excepting  those  at  the  level  of  the  surface  of  the  fluid. 

If  a  finger  he  plunged  into  a  heavy  fluid,  as  metallic  mercury, 
the  part  submerged  hears  a  pressure  which  decreases  from  below 
upward  uniformly.  It  is  only  at  the  surface  of  the  liquid  that  a 
marked  inequality  of  pressure  exists.  It  follows  a  circular  line 
which  surrounds  the  finger  at  this  level  and  can  he  plainly  felt  by 
the  individual.  If  a  lighter  fluid,  as  water,  be  used,  the  pressure 
sensation  is  but  very  slight. 

Compound  Tactile  Sensations. — These  may  be  simultaneous 
or  successive.  Simultaneous  tactile  sensation  may  be  either  double 
or  multiple.  Double  sensations,  whether  of  contact,  pressure,  or 
traction,  are  shown  only  when  the  stimuli  are  applied  at  a  certain 
distance  from  one  another.  If  the  stimuli  be  near  enough,  the  sen- 
sation remains  single  even  though  the  stimulus  has  been  applied  to 
the  skin  in  two  places.  The  earliest  systematic  experiments  upon 
this  subject  were  by  Weber.  He  touched  the  various  points  of  the 
skin's  surface  with  a  pair  of  carpenter's  compasses  and  then  observed 
the  distance  of  separation  necessary  to  give  a  distinct  impression  of 
two  points  of  contact.  The  instrument  now  used  for  this  purpose  is 
the  ccstliesiometer.  From  the  table  compiled  by  Weber  it  is  found 
that  the  tip  of  the  tongue  is  most  sensitive,  while  the  thigh  and  arm 
are  least  so.  In  the  case  of  the  tongue,  the  threshold  stimulus,  the 
minimum  separation  necessary  for  the  impression  of  double  contact 
is  but  1.1  millimeter;  67.6  millimeters  are  necessary  in  the  case  of 
the  thigh  and  arm.  The  connection  between  the  mental  and  physical 
conditions  explains  certain  illusions  of  tactile  sensations.  Of  these, 
the  Lest  known  is  the  so-called  experiment  of  Aristotle.  Wlien  a 
pea  or  small  ball  is  rolled  between  the   crossed  index  and  middle 


TACTILE  SENSE 


661 


fingers  of  a  blindfolded  person  there  results  a  sensation  of  Iwo  halls 
being  present  instead  of  one. 

There  are  spots  of  temperature  which  have  been  worked  out  by 
Goldscheider.  They  are  found  to  be  arranged  in  a  linear  manner 
and  generally  radiate  from  certain  points  of  the  skin,  usually  the 
hair-roots.  The  chain  of  "cold-spots"  does  not  coincide  with  those 
of  "warmth-spots."  The  sensation  of  cold  occurs  at  once;  that  of 
heat  develops  gradually.  As  a  rule,  the  cold-spots  are  more  abund- 
ant over  the  entire  body  surface.  The  hot-spots  may  be  quite  absent. 
The  minimal  distance  on  the  forehead  for  cold-spots  is  0.8  milli- 
meters while  for  warmth-spots  it  is  5  millimeters. 


Fig.  300. — Topography  of  Sensibility  to  Cold  and  Heat  in  the  same 
Region  of  the  Anterior  Surface  of  tlie  Thigh.     (Goldscheider,  HEDO?f.) 

a.  Cold  spots.  I,  Hot  spots.  Most  sensitive  spots  in  black;  moderately  sensi- 
tive spots  are  hatched;  spot  feebly  sensitive,  in  points;  spots  which  are  white 
are  not  sensitive. 


Protection  of  the  Organs  of  Touch. 

The  means  are  the  cutaneous  oil  and  the  hornij  appendages.  The 
cutaneous  oil  is  the  product  of  the  sebaceous  glands  of  the  skin. 
They  are  found  in  every  area  of  the  skin,  but  are  less  numerous  than 
the  sudorific  glands  except  in  the  palms  of  the  hands  and  soles  of 
the  feet.  They  may  be  large,  as  in  the  nose;  these  usually  have 
fine,  downy  hairs  near  their  mouths. 

The  sebaceous  glands  are  situated  more  superficially  than  the 
sweat-glands.     They  are  white  granules  annexed  to  the  hair-follicle. 


662  PHYSIOLOGY. 

in  which  their  excretory  duet  ends.  Their  size  is,  in  general,  in- 
verse to  the  volume  of  the  corresponding  hair-follicle.  Where  the 
hairs  are  large  the  sebaceous  glands  seem  to  be  appendages,  and 
when  the  hairs  are  small  its  hair-follicle  seems  to  be  an  appendage 
of  the  sebaceous  gland.  The  glands  are  aciniform,  surrounded  by 
a  thin,  connective  tissue  with  a  basement  membrane  studded  with 
epithelial  cells  infiltrated  with  fat,  and  the  cells  are  more  fatty  in 
the  direction  of  the  excreting  duct,  where  is  found  free  fat,  due  to 
the  destruction  of  the  cells.  When  the  sebaceous  secretion  stagnates, 
it  forms  a  fatlike  mass  which,  when  expressed,  as  in  the  nose,  forms 
the  comedo,  a  wormlike  body.  The  black-heads,  as  they  are  called, 
are  dirt  in  the  surface  of  the  gland.  When  the  comedo  is  pressed 
out  of  the  duct  it  has  been  mistaken  as  the  head  of  the  worm.  The 
sebaceous  matter  contains,  even  in  healthy  individuals,  the  pimple- 
mite,  or  Demodex  folliculorum. 

There  are  three  varieties  of  sebaceous  secretions:  (1)  the  seba- 
ceous secretion  proper  of  the  skin,  (2)  the  vernix  caseosa  of  the  new- 
born child,  and  (3)  the  smegma  of  Tyson's  glands  of  the  prepuce. 

Function. — The  sebaceous  matter  anoints  the  hairs  with  oil  in 
their  progress  of  growth  from  the  skin.  The  greasiness  of  the  sur- 
face of  the  skin  caused  by  this  secretion  permits  the  dust  readily  to 
adhere,  which  makes  soap  necessary  to  remove  its  excess.  Seba- 
ceous secretion  is  made  up  of  olein,  palmitin,  cholesterin,  and  earthy 
phosphates. 

The  organ  of  touch  is  also  protected  by  the  horny  layer  of  the 

epidermis,  whose  cells  are  being  constantly  removed  by  friction  and 

as  constantly  renewed  by  proliferation  of  the  cells  of  the  cutis  vera. 

The  modifications  of  the  epidermis  in  man  are  the  hair  and  the 

nails. 

Hair. — The  hairs  are  threadlike  appendages  to  the  skin  project- 
ing from  almost  every  part  of  its  surface  except  the  palms  and  soles. 
They  are  flexible,  elastic,  and  shining,  but  vary  in  degree  of  develop- 
ment, fineness,  color,  and  form  in  different  races  and  the  sexes  as 
well  as  in  different  persons.  The  color  of  the  hair  varies  from  a 
light  color  to  a  black.  The  black  hairs  are  found  in  all  parts  of  the 
globe  and  in  all  latitudes,  as  in  the  Esquimaux,  negro,  Indian,  and 
Malay.  All  the  colored  races  have  black  hair,  and  this  is  true  in 
some  groups  of  the  white  race.  Red  hair  is  represented  in  all  races. 
The  hair  is  composed  of  a  projecting  part,  the  stem,  terminated  by 
the  point,  or  end.  The  portion  inserted  into  the  skin  is  the  root, 
which  begins  in  a  clublike  expansion.     The  hairs  generally  project 


TACTILE  SENSE.  663 

obliquely  from  the  skin.  The  hairs  of  the  white  race  are  cylindrical ; 
the  hair  of  the  negro  flattened  cylindrical.  In  structure  the  hairs 
consist  of  an  exterior  cuticle,  a  cortex,  and  an  interior  medulla. 
The  cuticle  consists  of  a  single  layer  of  thin,  colorless,  quadrilateral 
scales  which  overlap  like  the  shingles  of  a  roof.  The  edges  of  the 
scales  are  directed  upward  and  outward  along  the  shaft.  The  cortex 
makes  the  chief  part  of  the  hair,  and  it  is  that  upon  which  the  color 
of  the  hair  mainly  depends  in  different  individuals.  The  cortical 
layer  is  made  up  of  elongated,  fusiform  cells  containing  a  lineal 
nucleus.  When  the  coloring  matter  disappears  in  the  cortex  the  hair 
becomes  white.  The  medulla  is  frequently  absent,  especially  in  the 
dark-colored  hairs.  It  occupies  the  axis  of  the  hair.  It  consists  of 
cuboidal  cells  with  granular  contents  and  an  indistinct  nucleus.  The 
medullary  substance  is  generally  mingled  with  more  or  less  air,  in 
small  bubbles,  which  penetrates  from  the  ends  of  the  hairs  and  gives 
to  these  when  white  the  characteristic  silver  luster.  The  root  of  the 
hair  is  lodged  in  a  flask-shaped  receptacle  of  the  skin  called  the  hair- 
follicle,  at  the  bottom  of  which  is  a  papilla  from  which  the  hair 
grows.  "Goose-flesh"  is  due  to  minute  muscles  contracting  and 
causing  the  hair-follicles  to  become  erect.  At  the  same  time  the 
sebaceous  glands  are  compressed,  favoring  the  exudation  of  the  seba- 
ceous secretion. 

Chemically,  the  hairs  are  mainly  composed  of  an  albuminoid 
derivative,  keratin,  in  which  a  notable  quantity  of  sulphur  is  present: 
about  5  per  cent.  In  the  ashes  are  found  the  phosphates,  earthy  sul- 
phates, oxide  of  iron,  and  pigment. 

FuNCTiox. — The  large  hairs  serve  to  protect  the  skin,  breaking 
shocks  and  preventing  a  considerable  loss  of  heat.  In  other  places, 
like  the  armpits,  they  prevent  friction  and  attrition  of  the  skin 
layers.     The  downlike  hairs  render  the  touch  more  delicate. 

Nails. — The  nails  are  hard  appendages  of  the  skin,  and  corre- 
spond to  the  claws  of  animals.  They  are  flexible,  translucent, 
square-shaped  plates  continuous  with  the  epiderm  and  resting  on  a 
depressed  surface  of  the  dermis  called  the  matrix,  or  bed. 

The  exposed  part  of  the  nail  is  the  body  and  its  anterior  end  is 
its  free  border.  The  root  of  the  nail  is  lodged  in  a  deep  groove  of 
the  matrix  and  the  lateral  borders  are  received  into  shallow  grooves. 
The  half-moon,  or  lunule,  of  the  nail  is  due  to  a  less  degree  of  vascu- 
larity of  the  matrix  at  the  root,  defined  by  a  semicircular  line.  The 
horny  layer  corresponds  to  the  cuticle  of  the  epiderm,  and  is  com- 
posed of  flattened,  nucleated  cells.     The  soft  layer  of  the  nails,  the 


664  PHYSIOLOGY. 

stratum  mucosum,  corresponds  to  that  layer  of  the  cpiderm.  The 
nails  grow  in  length  by  new  cells  at  the  root,  in  thickness  by  addi- 
tions beneath  the  nail. 

The  nails  serve  to  protect  the  skin  at  the  tips  of  the  phalanges, 
and,  at  the  same  time,  perfect  the  touch  of  the  fleshy  parts  of  the 
fingers.  The  average  growth  of  the  nails  is  about  one-eighth  of  an 
inch  per  month. 


CHAPTER  XVI. 

SPECIAL  SENSES  (Continued.) 

THE  SENSE  OF  TASTE. 

Taste  is  an  organ  of  special  sense,  by  which  as  a  medium  the 
individual  perceives  savory  impressions.  Its  principal  uses  to  the 
economy  are  two:  First,  it  acts  as  a  guide  to  the  individual  in  his 
choice  of  food,  at  the  same  time  rendering  its  mastication  a  matter 
of  some  pleasure.  Secondly,  it  excites  the  salivary  glands  reflexly,  so 
that  they  pour  out  their  juices  into  the  mouth. 

The  organ  of  taste  is  seated  in  the  oral  cavity  and  in  the  mucous 
membrane  of  the  tongue.  Its  limits  are  not  well  defined.  The  diffi- 
culty in  their  determination  depends  upon  the  double  fact  that  these 
organs  of  taste  are  endowed  with  a  very  delicate  sensibility  of  a 
tactile  nature,  and  that  the  gustatory  sensibility  and  the  organ  of 
smell  are  in  very  close  proximity  to  one  another.  For  these  reasons 
one  may  very  easily  believe  that  certain  regions  of  his  mouth  are 
gustatory,  when  in  reality  the  substances  which  have  touched  them 
have  only  produced  tactile  or  olfactory  impressions. 

Still  it  has  been  shown  that  the  principal  regions  of  the  oral 
mucous  membrane  designed  to  perceive  taste-impressions  are  at  the 
base  and  edges  of  the  tongue.  In  a  secondary  degree,  also,  gustatory 
impressions  are  perceived  in  the  anterior  surface  and  edge  of  the 
soft  palate,  and  the  anterior  portion  of  the  tongue.  All  other  por- 
tions of  the  mouth  are  incapable  of  taste-impressions. 

The  Ton^e. — The  principal  organ  of  the  sense  of  taste  is  un- 
doubtedly the  tongue.  Its  anatomical  structure  as  a  muscular  organ 
has  already  been  described  when  discussing  deglutition  and  the  part 
it  i^layed  in  the  role  of  that  important  function.  At  this  time  it 
remains  but  to  review  such  portions  as  have  a  direct  bearing  upon 
its  role  as  a  gustatory  member. 

There  are  three  kinds  of  papillae  in  the  mucous  membrane  of 
the  tongue:  the  circumvallate,  fungiform,  and  filiform.  They  extend 
from  the  tip  of  the  tongue  to  the  foramen  caecum.  The  papillae  con- 
sist of  elevations,  visible  to  the  naked  eye  and  covered  with  strati- 
fied, squamous  epithelium.  The  central  body  of  each  papilla  con- 
tains connective  tissue,  blood-  and  lymph-vessels,  and  nerves. 

(G65) 


666  PIIYSIOLOGY. 

The  circumvallate  papilla-,  the  largest  of  the  varieties  and  about 
a  dozen  in  number,  J'onu  a,  \'-like  low,  defining  the  papillary  layer 
at  the  posterior  third  of  the  tongue.  They  have  the  fomi  of  an 
inverted  cone  surrounded  by  a  ringiike  wall-elevation. 

The  fungiform  are  next  in  size,  and  more  numerous  than  the 
circumvallate.  They  are  small,  red  eminences  scattered  over  the  sur- 
face of  the  tongue,  but  are  especially  numerous  at  and  near  the  tip. 
They  are  rounded  at  the  free  extremity  and  narrower  at  the  point  of 
attachment  to  the  tongue. 

The  filiform  papilla?,  smaller  and  more  numerous  than  the 
others,  are  crowded  in  the  spaces  between  the  others,  but  are  ar- 
ranged in  rows  diverging  from  the  median  line  of  the  tongue. 

Nerves. — The  tongue  receives  three  nerves:  one  of  motion,  the 
hypoglussal,  which  animates  the  muscles;  and  two  other  sensory 
branches — the  lingual  branch  of  the  glosso-pharyngeal  and  the  lingual 
branch  of  the  trigeminus.  The  former  of  the  hitter  two  branches 
spreads  in  the  mucous  membrane  at  the  base  and  edges  of  the  tongue; 
the  latter  is  distributed  to  the  mucous  membrane  of  the  anterior  two- 
thirds  of  the  tongue.  The  branches  of  the  glosso-pharyngeal  are 
especially  concerned  in  sensations  of  hitterriess,  while  the  branches  of 
the  trigeminus  are  affected  principally  by  siveet  and  acid  tastes. 

Section  of  the  hypoglossal  upon  both  sides  causes  paralysis  of  the 
tongue  without  injuring  its  tactile  or  gustatory  sensibilities.  Section 
of  the  lingual  branch  of  the  trigeminus  causes  only  loss  of  fine  tactile 
sensibility  and  gustatory  sensibility  of  the  anterior  two-thirds  of 
the  tongue. 

Section  of  the  glosso-pharyngeal  causes  loss  of  tactile  and  gusta- 
tory sensibility  in  the  mucous  membrane  at  the  base  of  the  tongue. 
Such  an  animal  can  swallow  bitter  and  nauseous  substances,  like 
colocynth,  with  impunity. 

The  gustatory  action  of  the  lingual  branch  of  the  trigeminus 
comes  from  the  chorda  tympani.  The  latter  is  a  small  nerve  which 
begins  in  the  facial  and  traverses  the  middle  ear  to  join  the  lingual 
branch  at  the  level  of  the  pterygoid  muscles. 

The  chorda  tympani  nerve  passes  from  the  tongue  to  the  nerve- 
centers  through  the  lingual  nerve,  the  facial,  and  finally  through  the 
intermediate  nerve  of  Wrisberg. 

Taste-organs. — The  terminal  branches  of  the  glosso-pharyngeal 
nerve  end  in  the  taste-bulbs.  The  taste-bulbs  are  oval  bodies  imljedded 
in  the  epithelial  layer.  Each  taste-bulb  is  fomied  of  two  kinds  of 
elongated  epithelial  cells,  and  their  whole  outline  is  barrel-shaped. 


THE  SENSE  OF  TASTE. 


667 


The  taste-cells  are  narrow  and  slightly  thickened  in  the  iniddle,  where 
the  nucleus  is  situated.  The  taste-bulbs  occur  chiefly  on  the  sides  of 
the  circumvallate  papilla,  although  a  small  number  of  them  are  on 
the  fungiform  and  the  soft  palate.  The  ends  of  the  taste-bulbs  near 
the  surface  have  a  minute,  funnel-like  opening  called  the  taste-pore. 
The  number  of  taste-bodies  is  very  great.  If  the  glosso-pharyngeal 
nerve  is  cut,  the  taste-bodies  degenerate. 

The  proper  stimuli  for  the  end-bulbs  of  the  gustatory  nerves  are 
the  savory  substances.  These  must  be  dissolved  in  the  liquids  of  the 
mouth  before  they  can  penetrate  the  outer  cells  of  the  mucous  mem- 
brane to  come  into  contact  with  the  nerve-filaments  in  the  imbedded 


Fig.  301. — Structure  of  the  Taste-organs.      (Lais'dois.) 

I.  Transverse  section  of  a  circumvallate  papilla.  W,  the  papilla,  v,  r.  The 
wall  in  sections.  R,  R,  The  circular  slit,  or  fossa.  A",  A',  The  faste-bulbs  in 
position.     N,  N,  The  nerves. 

II.  Isolated  taste-bulbs.  D,  Supporting,  or  protective,  cells.  K,  Lower 
end.     E,   Free  end,   open  with  the   projecting  apices  of   the   taste-cells. 

III.  Isolated  protective  cell  (d)  with  a  taste-cell  (r). 

bulbs.  The  most  suitable  temperature  for  the  thorough  testing  of 
liquids  is  100°  F. 

The  intensity  of  the  gustatory  impression  depends  upon  various 
factors:  the  nature  of  the  substance,  the  duration  of  the  impression, 
sensibility  of  the  region  touched,  and  the  stimulating  action  of  the 
substance  upon  the  mucous  membrane.  The  flavor  of  a  substance 
does  not  depend  upon  its  chemical  properties,  for  both  quinine  and 
sulphate  of  magnesia  are  bitter;  sugar,  chloroform,  and  glycerin  are 
sweet. 

Improper  stimuli  give  gustatory  impressions.  Thus,  the  galvanic 
current  applied  to  the  tongue  gives  an  acid  taste  at  the  positive  pole 
and  a  weaker,  alkaline  taste  at  the  negative  pole. 


668  PHYSIOLOGY. 

Varieties  of  Substances. — Of  the  gustatory  substances  there  are 
four:  (1)  sweet,  (2)  hitter,  (3)  acid,  and  (4)  saline.  In  addition 
to  these  fundamental  substances  there  are  compound  gustatory  im- 
pressions, or  a  confusion  of  gustatory  sensations  with  those  which  are 
tactile  or  olfactory.  Thus,  there  is  known  the  piquant  taste  of 
cheese,  the  caustic  taste  of  mustard,  and  the  aromatic  taste  of 
strawberries. 

The  acid  and  siveet  tastes  are  best  perceived  at  the  tip  and  edges 
of  the  tongue;  the  salty  and  hitter  tastes  are  comprehended  at  the 
hase.  This  leads  to  the  result  that  some  substances  have  a  different 
taste,  dependent  upon  whether  they  touch  the  tip  or  the  base  of  the 
tongue.  Thus,  acetate  of  potassium  at  the  tip  of  the  tongue  is  acid, 
and  at  the  base  it  is  bitter. 


Fig.  302. — Sternberg's  Gustometer. 

The  four  primitive  tastes  are  not  all  perceived  at  the  exact  time 
of  their  impression  upon  the  tongue.  The  salty  is  first  perceived, 
then, the  sweet,  next  the  acid,  and  last  the  bitter. 

Tactile  sensations  by  astringents  (tannic  acid)  or  thermal  sensa- 
tions (mustard)  are  usually  confounded  with  taste  proper.  The  taste 
of  vanilla  is  but  an  olfactory  impression. 

Drugs. — By  the  action  of  drugs  one  is  able  to  abolish  certain 
tastes  more  readily  than  others.  Cocaine  upon  the  tongue  abolishes 
tactile  sensations  and  the  taste  for  bitter  things,  but  does  not  inter- 
fere with  voluntary  movement. 

The  leaves  of  Gymnema  sylvestre,  when  chewed,  destroy  the  sense 
of  taste  for  bitters  and  sweets,  while  that  for  salts  and  acids  remains. 

The  Taste-center,  to  which  the  gustatory  nerves  send  their  im- 
pressions, lies  in  the  vnci?iate  gyrus. 

Sternberg's  Gustometer. — This  instrument  consists  of  a  Eichard- 
son  double-bellows  rubber  bulb,  which  is  attached  to  a  two-way  stop- 
cock. The  two-way  stopcock  is  connected  by  rubber  tubes  with  two 
glass  bulbs  fitted  with  an  entrance  and  an  exit  tube.  Both  glass 
bulbs  contain  small  pieces  of  sponge,  to  increase  the  surface  for 


THE  SENSE  OF  TASTE.  669 

evaporation  of  the  volatile  fluids.  In  one  glass  bulb  is  placed  chloro- 
form as  a  sweet  substance  to  be  tasted;  in  the  other  glass  bulb, 
ether,  to  represent  a  bitter-tasting  substance.  To  the  exit  tubes  of 
each  glass  bulb  are  attached,  by  rubber  tubes,  two  tubes  of  glass 
drawn  to  a  fine  point.  A  spring  clip  is  placed  on  each  rubber  con- 
necting-tube. When  the  apparatus  is  to  be  used,  the  Eichardson 
rubber  bulb  is  compressed  and  air  is  driven  through  one  or  the  other 
glass  bulb.  By  this  means  we  can,  at  our  pleasure,  test  for  bitter 
or  sweet  substances.  Even  acetic  acid  can  be  placed  in  one  of  the 
bulbs,  to  test  the  taste  for  acids. 

The  pointed  glass  tubes  must  be  brought  near  the  point  on  the 
tongue  to  be  tested,  but  they  must  not  touch  it. 

Sternberg  has  also  constructed  a  quantitative  gustometer,  on  the 
same  principle  as  the  olfactometer  of  Zwaardemaker. 


CHAPTER  XVII. 

SPECIAL  SENSES  (Continued.) 

THE  SENSE  OF  SMELL. 

The  seat  of  the  sense  of  smell  resides  in  the  cavities  of  the  nose. 
Ivant  has  very  aptly  spoken  of  smell  as  "taste  at  a  distance.'^ 

The  organ  of  smell  resembles  those  of  sight  and  hearing  in  that 
it  consists  of  a  special  nerve  which  ends  in  a  specialized  epithelium. 
In  this  case  the  special  nerve  is  the  olfactory;  the  specialized  epithe- 
lium is  the  mucous  membrane  of  the  upper  portion  of  the  nasal 
cavity.     It  is  in  this  portion        the  mucous  membrane  that  the  fila- 


i  BouLtUAZ 


Fig.  303. — Innervation  of  the  External  Wall  of  the  Nasal  Fossa. 
(Testut.) 

1,  Olfactory  tract.  2,  Olfactory  bulb.  3,  Branches  of  olfactory  nerve.  5, 
Ganglion  of  Meckel.  6,  Pharyngeal  nerve.  7,  Vidian  nerve.  8,  9,  Spheno- 
palatine. 10,  11,  12,  12',  Palatine  nerves  with,  13,  nasal  branch.  14,  14',  Termina- 
tion of  ethmoidal  nerve.     15,  Opening  of  Eustachian  tube.     16,   Vault  of  palate. 


ments  of  the  olfactory  nerve  are  distributed.  For  that  reason  it  has 
been  termed  the  ref/io  olfacforia,  and  comprises  the  upper  portion  of 
the  septum,  the  upper  turbinated,  and  part  of  the  middle  turbinated 
regions.  All  other  portions  of  the  nasal-cavity  covering  is  known  as 
the  regio  respiratoria,  or  simply  the  Schneiderian  membrane.  During 
ordinary  respiration  the  currents  of  air  in  their  passage  in  and  out 
(670) 


THE  SENSE  OF  SMELL. 


671 


are,  for  the  most  part,  confined  to  this  latter  region.  The  mucous 
membrane  which  covers  this  portion  of  tlie  nasal  cavity  is,  in  struc- 
ture and  appearance,  very  similar  to  that  of  the  trachea.  It  is  com- 
posed of  layers  of  ciliated  epithelium  which  rest  upon  a  basement 
membrane  rich  in  blood-vessels  and  lymphatics.  Among  the  ciliated 
cells  are  found  numerous  goblet  and  mucous  cells,  whose  secretions 
keep  the  surface  of  the  mucous  membrane  soft  and  moist.  In  it  are 
numerous  filaments  of  the  trigeminus,  which  endow  it  with  tactile 


.^  -^i 


Fig.  304.     (Bishop.) 

1,  Middle  turbinated  body  turned  aside  and  held  by  a  hook.  2,  Nasal  duct' 
and  valves.  3,  Canal  leading  to  the  maxillary  and  frontal  sinuses.  4,  Inferior 
turbinated  body  showing  the  location  of  the  mouth  of  the  nasal  duct  in  the 
ciil-de-sac. 

sensibility.     There  are  710  filaments  of  the  olfactory  nerve  in  this 
region. 

The  olfadorij  mucous  membrane  is  thicker  than  that  of  the 
respiratory  portion.  To  the  naked  eye  it  presents  a  yellow  or  brown- 
yellow  color  because  of  the  pigment  contained  within  it.  By  reason 
of  its  color  it  is  very  readily  distinguished  from  that  of  the  Schneider- 
ian  membrane.  Its  surface  is  covered  by  a  single  layer  of  cylindrical 
epitheUum  whose  cells  are  often  branched  at  their  lower  ends. 


672 


PHYSIOLOGY. 


The  olfactory  region  contains  the  olfactory  cells.  These  possess 
a  body  of  spindle  shape  with  a  large  nucleus  containing  nucleoli.  In 
the  deeper  part  the  olfactory  cells  pass  into  and  become  continuous 
with  fine  fibers.    These  last  pass  into  the  olfactory  nerve. 

The  olfactory,  the  nerve  of  smell,  issues  by  two  roots,  each  from 
the  corresponding  hemisphere.  The  fibers  are  composed  of  medul- 
lated  and  nonmedullated  fibers. 

These  latter  fibers  proceed  from  the  olfactory  bulb. 


Fig.   305. — Diagram  of  the  Connections  of  Cells  and  Fibers  in  the 
Olfactory  Bulb.     (.Schafer,  in  Quain's  Anatomy.) 

oJf.c,  Cells  of  the  olfactory  mucous  membrane,  olf.n,  Deepest  layer  of  the 
bulb,  composed  of  the  olfactory  nerve-fibers  which  are  prolonged  from  the  olfac- 
tory cells.  {/I,  Olfactory  glomeruli,  containing  arborization  of  the  olfactory 
nerve-fibers  and  of  the  dendrons  of  the  mitral  cells,  me,  mitral  cells,  a.  Thin 
axis-cylinder  process  passing  toward  the  nerve-fiber  layer,  n.tr,  of  the  bulb  to 
become  continuous  with  fibers  of  the  olfactory  tract;  these  axis-cylinder  proc- 
esses are  seen  to  give  off  collaterals,  some  of  which  pass  again  into  the  deeper 
layers  of  the  bulb,  ii',  A  nerve-fiber  from  the  olfactory  tract  ramifying  in  the 
gray  matter  of  the  bulb. 

The  olfactory  bull)  is  a  part  of  the  cerebral  cortex  and  is  an  oval 
or  club-shaped  mass  of  gray  matter  which  rests  on  the  cribriform 
plate  of  the  ethmoid  bone,  through  the  foramen  of  which  it  is  con- 
nected with  the  olfactory  nerves.  The  olfactory  nerves  are  twenty 
in  number  and  are  the  central  coursing  of  the  neuraxons  of  the  rod- 
shaped  olfactory  nerve-cells  in  the  olfactory  region  of  the  nose.  They 
pass  through  the  openings  in  the  cribriform  plate  and  terminate  in 


THE  SENSE  OF  SMELL.  673 

arborizations  about  the  dendrons  of  the  mitral  cells  of  the  olfactory 
glomeruli.  These  bipolar  cells  greatly  resemble  the  cells  of  a  gan- 
glion of  a  posterior  root  of  the  spinal  cord,  one  ueuraxon  going  to  the 
olfactory  mucous  membrane  and  the  central  neuraxon  going  to  the 
olfactory  bulb. 

The  olfactory  bulb  from  without  inward  consists  of  four  layers : — 

1.  The  nerve-fibers. 

2.  Stratum  glomerulosum. 

3.  Stratum  gelatinosum. 

4.  Layer  of  central  nerve-fibers. 

In  the  first  layer  each  fibril  is  a  central  ueuraxon  of  a  rod-shaped 
nerve-cell  from  the  olfactory  mucous  membrane.  The  fibers  of  the 
olfactory  nerves  pass  into  the  glomeruli  lying  beneath.  Within  the 
glomerulus  the  endings  of  the  olfactory  fibrils  come  in  contact  with 
an  olfactory  end-brush  of  an  apical  dendron  of  a  mitral  cell. 

In  the  stratum  glomerulosum  each  glomerulus  consists  of  the 
terminal  arborizations  of  an  olfactory  nerve-fiber,  together  with  the 
olfactory  end-brushes  from  the  apical  dendrons  of  the  mitral  cells. 

The  stratum  gelatinosum  in  its  inner  part  contains  two  chief 
forms  of  cells:  the  deep  and  superficial  layers  of  mitral  cells  which 
correspond  to  the  pyramidal  cells  of  the  cerebral  cortex. 

The  fourth  layer  in  its  outer  part  has  a  large  number  of  very 
small  granular  cells  between  which  pass  the  descending  neuraxons  of 
the  mitral  cells.  The  nerve-fibers  of  the  olfactory  bulbs  collect  at 
their  posterior  extremities  into  two  bundles:  the  olfactory  tracts. 
The  outer  root-fibers  of  the  olfactory  tract  come  into  relation  with 
the  gyrus  hippocampus,  the  uncus,  and  cornu  ammonis.  The  inner 
root-fibers  pass  into  the  gyrus  fornicatus. 

Olfactory  Sensations. — The  student,  in  order  to  obtain  clear-cut 
ideas  as  to  the  mechanism  of  the  special  sense  of  smell,  should  bear 
in  mind  the  principle  of  the  arrangement  of  the  olfactory  nerve- 
terminations.  It  is  recalled  that  within  the  mucous  membrane  lie 
the  olfactory  cells.  From  the  peripheral  end  of  each  cell  project 
seven  or  eight  ciliumlike  processes.  These  not  only  project  to  the 
surface  of  the  mucous  membrane,  but  even  to  the  surface  of  the  serous 
fit  id  moistening  the  membrane.  Thus,  the  terminal  filaments  are 
placed  in  an  exposed  position  so  that  they  may  very  readily  respond 
to  any  irritant. 

The  proper  stimulus  for  olfactory-nerve  filaments  are  odorous 
siibstances  which  reach  the  regio  olfactoria  through  the  air  and  must 
be  in  a  volatile  state.     Hence,  olfactory  sensations  are  produced  by 


674  PHYSIOLOGY. 

volatile,  odorous  particles  coming  into  direct  contact  with  the  exposed 
nerve-filaments  during  the  act  of  inspiration.  As  the  regio  olfactoria 
is  in  the  highest  position  of  the  nasal  cavity,  it  becomes  necessary  for 
the  individual  to  cause  the  inspired  air  forcibly  to  reach  this  area. 
This  is  accomplished  by  an  act  ordinarily  known  as  "sniffing." 

During  ordinary  respiration  the  inspired  and  expired  air  courses 
along  close  to  the  septum  and  below  the  inferior  turbinated  bone. 
Should  the  respired  air  be  heavily  charged  with  odorous  particles,  of 
course  some  will  find  their  way  into  the  regio  olfactoria,  as  the  air 
in  this  compartment  is  gradually  changed.  There  will  then  result 
a  sensation  of  smell,  but  it  will  be  faint  and  not  so  sharply  defined 
as  when  the  person  sniffs.  By  the  latter  process  the  air  is  changed 
more  quickly  and  a  greater  number  of  volatile  particles  irritate  the 
exposed  nerve-endings,  with  the  result  of  a  sharply  defined  sensation. 
The  sensation  seems  to  occur  at  the  first  moment  of  contact  of  the 
odorous  particles  with  the  mucous  membrane.  The  olfactory  nerve 
tires  very  quickly  when  an  odor  acts  for  a  certain  time;  the  effect 
becomes  weaker  and  weaker  little  by  little,  until  the  odor  is  finally 
unperceived. 

Should  the  free  movement  of  the  air  be  prevented — as,  for 
example,  when  nasal  catarrh  brings  on  a  tumefaction  of  the  mucous 
membrane  of  the  inferior  turbinate, — the  odorous  impression  cannot 
take  place. 

In  case  many  different  odors  act  simultaneously  upon  one  nasal 
cavity,  the  individual  receives  a  mixed  sensation.  Should  but  two 
odors  act,  the  one  is  perceived  on  the  right  half  of  the  mucous  mem- 
brane of  the  cavity,  the  other  upon  the  left  half.  This  is  not  a 
true  mixture,  for  the  person  perceives  slightly  the  one  odor  and 
slightly  the  other.  One  part  of  vanillin  to  10,000,000  can  be  recog- 
nized by  the  sense  of  smell. 

Secondaky  Sensation. — The  olfactory  impression  having  been 
made,  the  secondary  after-sensation  often  remains  for  a  long  time. 
This  is  particularly  the  case  with  strong,  disagreeable  odors.  This 
phenomenon  is  explained  on  the  supposition  that  the  odorous  parti- 
cles remain  in  the  cavity  of  the  nose,  even  in  the  air.  It  is  not 
believed  that  the  manifestation  is  due  to  persistence  of  excitation  of 
the  olfactory  nerve-fibers  after  the  stimulus  has  been  removed. 

There  are  subjective  olfactory  sensations  which  are  true  hallucina- 
tions. They  are  often  met  with  in  demented,  in  hysterical,  or  in 
pregnant  women.  These  sensations  owe  their  existence  to  some 
material  alteration  of  the  nervous  apparatus. 


THE  SENSE  OF  SMELL.  675 

From  impressions  truly  olfactory  it  becomes  necessary  to  dis- 
tinguish the  gustatory  as  well  as  tactile  or  irritative  sensations  upon 
the  nasal  mucous  membrane.  The  irritation  and  even  pain  produced 
by  the  vapors  of  ammonia  often  lead  it  to  be  improperly  classed  as 
"having  a  bad  odor."  Experimentally,  a  dog  with  both  olfactories 
divided  always  starts  from  the  odor  of  ammonia  or  of  acetic  acid. 
This  is  due  to  painful  stimulation  of  his  Schneiderian  membrane, 
which  gets  its  sensory  nerve-filaments  from  the  second  branch  of  the 
trigeminus. 

Uses. — The  organ  of  smell  represents  an  advance  sentinel  for 
the  functions  of  respiration  and  alimentation.  Among  the  lower 
animals  it  serves  for  the  recognition  of  sex. 


Fig.  306. — Zwaardemaker's  Olfactometer.  ( Tigerstedt. )  (From 
Tigerstedt's  "Human  Physiology,"  copyright,  1906,  by  D.  Appleton  and 
Company. ) 

Hyperosmia  and  Anosmia, — Hyperosmia,  or  increased  sensitive- 
ness of  smell,  is  a  common  condition.  It  is  very  apt  to  be  found 
among  the  hysterical  and  in  many  other  nervous  disorders.  Strych- 
nine is  one  of  the  drugs  which  is  capable  of  producing  this  condition 
when  it  is  applied  locally  in  solution. 

Anosmia  is  a  term  used  to  designate  a  condition  which  is  the 
reverse  of  the  beforementioned.  It  may  be  complete,  when  it  is 
usually  congenital.  In  such  a  case  the  olfactory  nerves  are  absent. 
It  is  more  usual,  however,  to  find  the  condition  partial.  Its  causes 
may  be  stenosis  of  the  nasal  cavities,  disease  of  the  olfactory  mucous 
membrane,  or  nervous  diseases.  Strychnine  often  relieves  the  con- 
dition. 

The  local  application  of  a  dilute  solution  of  strychnia  heightens 
the  sense  of  smell  (hyperosmia).     Smoking,  the  local  application  of 


676  PHYSIOLOGY. 

morphia  and  cocain  produce  partial  loss  of  the  sense  of  smell 
(anosmia). 

Certain  odors  can  antagonize  another  odor  when  perceived  by 
separate  nostrils,  so  that  no  odor  is  perceived,  as  acetic  acid  and 
ammonia.  There  is  also  a  relationship  between  smell  and  the 
chemico-physical  properties  of  odors;  it  follows  the  periodic  law  of 
Mendelcjeff. 

The  Center  of  Smell  lies  in  the  tip  of  the  uncinate  gyrus  upon 
the  inner  surface  of  the  cerebral  hemisphere. - 

Zwaardemaker's  Olfactometer.— Eubber  tubing,  two  inches  in 
length,  is  fitted  inside  a  glass  tube,  which  prevents  any  particles  of 
odor  leaving  its  surface.  Another  glass  tube  is  closely  fitted  inside 
the  rubber  tube.  When  the  inner  glass  is  drawn  out  .7  centimeters, 
then  a  normal  person  can  perceive  the  odor  of  rubber,  when 
air  is  drawn  through  the  inner  graduated  glass  tube.  Hence  the 
inner  glass  rod  was  graduated  in  degrees  of  .7  centimeters.  If  a  man 
can  only  perceive  rubber  at  1.4  centimeters,  he  has  only  half  normal 
olfaction;  but  in  certain  cases  of  considerable  want  of  olfaction  the 
odor  of  rubber  is  not  strong  enough  to  be  perceived.  Here  he  used 
a  tube  of  "gutta  percha  ammoniacum,"  which  is  twenty-four  times 
more  powerful  as  a  stimulus  than  india  rubber.  It  was  found,  in 
many  cases  of  anosmia,  that  certain  odors  might  be  smelt  to  a  nor- 
mal extent,  whilst  others  barely  stimulated  the  olfactory  organs. 


CHAPTER   XVIII. 

SPECIAL  SENSES  (Continued.) 

THE  SENSE  OF  HEARING. 

By  means  of  the  special  sense  of  hearing  the  individual  gains 
knowledge  of  a  kind  differing  from  the  Just-mentioned  senses.  It 
does  not  tell  him  what  is  going  on  in  the  outer  world  by  actual  con- 
tact, as  in  touch  or  taste;  nor  yet  by  particles  of  matter  impinging 
upon  the  exposed  end  of  nerve-filaments,  as  in  the  sense  of  smell. 
In  the  special  sense  of  hearing  the  impressions  conveyed  to  the  cen- 
tral nervous  system  are  produced  by  wavelike  vibrations  in  the  sur- 
rounding air.  For  the  reception  of  these  vibrations,  so  that  they 
may  be  properly  interpreted  and  the  corresponding  impressions  con- 
veyed to  the  brain,  it  becomes  necessary  to  have  a  special  sense- 
organ:   the  ear. 

The  Ear. 

The  organ  of  hearing  in  its  greatest  simplicity  may  be  repre- 
sented by  a  small  membrane  stretched  like  a  drumhead  over  the 
bottom  of  a  funnel-shaped  tube.  The  tube  opens  upon  the  surface 
of  the  body  so  that  it  is  in  direct  communication  with  the  enveloping 
atmosphere.  The  membrane  is  so  disposed  that  it  is  readily  thrown 
into  vibrations  when  the  external  air  becomes  undulatory  as  the 
result  of  vibrations  of  some  body.  Its  vibrations  are  communicated 
to  an  inner  vesicle  that  is  filled  with  a  liquid.  The  liquid  is  like- 
wise thrown  into  waves  whose  imdulations  stimulate  the  ramifica- 
tions of  the  auditory  nerve  wdiich  are  spread  out  upon  the  walls  of 
the  vibrating  vesicle. 

Anatomy. — The  apparatus  for  hearing  is  composed  of  three 
parts:   external  ear,  middle  ear,  and  internal  ear. 

ExTEKNAL  Ear. — The  external  ear  is  composed  of  the  auricle 
and  external  auditory  meatus. 

The  auricle  has  the  form  of  an  irregularly  shaped  shell.  It  is 
composed  of  yellow,  elastic  cartilage  which  is  covered  over  with  skin. 
From  its  shape  one  might  readily  believe  that  the  function  of  the 
auricle  is  to  collect  and  reflect  sound-waves  into  the  auricle :  that  is, 
to  behave  in  the  capacity  of  an  ear-trumpet.     But  it  is  found  that 

(677) 


G78  PHYSIOLOGY. 

hearing  is  perfectly  normal  in  those  persons  from  whom  the  external 
ear  has  been  removed  by  accident  or  otherwise. 

The  external  auditory  meatus  and  canal  extend  from  the  concha 
of  the  auricle  to  the  tympanum.  The  canal  is  composed  partly  of 
cartilage  and  partly  of  bone;  the  bony  portion  belongs  to  the  tem- 
poral bone.  The  canal  is  lined  by  skin,  which  contains  modified 
sebaceous  and  sudoriferous  glands.  By  the  glands  is  secreted  the 
cerumen,  or  earwax. 

The  internal  end  of  the  auditory  canal  is  bounded  by  an  ellipsoid 
structure  which  is  composed  of  three  layers  of  tissue :  the  tympanic 
membram. 


-^ss 


Fig.  307. — Diagram  of  the  External  Surface  of  the  Left  Tymimnic 
Membrane.      (  Hensen.  ) 

a,  Head  of  malleus,  h,  Incus,  e,  Joint  between  malleus  and  incus.  Between 
c  and  d  is  the  flaccid  portion  of  the  membrane,  ax,  Axis  of  rotation  of  ossicles. 
The  umbo  is  the  deeply  shaded  part. 

Fimction  of  the  External  Ear. — Sound- vibrations  strike  the  ex- 
ternal ear,  some  of  which  go  directly  into  the  external  auditory 
meatus.  The  irregularity  of  the  surface  of  the  pinna  permits  us  to 
judge  more  correctly  of  the  direction  and  the  intensity  of  sound.  If 
these  irregularities  are  filled  up  with  wax,  while  the  meatus  is  left 
open,  the  intensity  of  sound  is  diminished,  and  it  is  more  difficult  to 
judge  of  the  direction.  In  the  external  meatus  the  waves  of  sound 
undergo  a  series  of  reflections,  which  conduct  them  to  the  membrana 
tympani.  By  reason  of  the  obliquity  and  curves  of  the  membrana 
tympani,  the  sound-waves  strike  it  in  a  nearly  perpendicular  direc- 
tion. The  external  ear  has  for  its  function  the  collection  and  trans- 
mission of  sounds  to  the  membrana  tympani.     The  horse  is  con- 


THE  SENSE  OF  HEARING.  679 

stantl_y  moving  his  ears  to  determine  the  direction  of  sounds,  but  in 
man  this  function  is  greatly  subordinated.  The  twisting  of  the 
mouth  of  the  meatus,  and  the  hairs  and  wax  in  the  external  meatus, 
also  keep  out  dust  and  insects. 

Auditory  Field. — Like  the  visual  field,  we  have  an  auditory  field. 
It  is  all  the  points  in  space  from  which  sound-waves  can  be  collected 
by  the  auricle  and  transmitted  by  the  auditory  canal.  Its  extent 
and  form  depend  upon  the  conformation  of  the  auricle. 

Middle  Eae,  ok  Tympanum. — The  tympanum  is  a  space  situ- 
ated within  the  substance  of  the  petrous  portion  of  the  temporal 
boue.     It  is  composed  of  tivo  hony  and  four  soft  parts. 


Fig.    -308. — Tympanic   Membrane   and   Auditory   Ossicles,   seen  from  the 
Tympanic   Cavity.      (Landois.) 

M,  Manubrium,  or  handle  of  the  malleus.  T,  Insertion  of  the  tensor  tym- 
pani.  h.  Head.  IF,  Long  process  of  the  malleus,  or  incus-tooth.  The  short 
(K)  and  the  long  (/)  process.  8,  Plate  of  the  stapes.  Ax  is  the  common  axis 
of  rotation  of  auditory  ossicles.  8,  The  pinion-wheel  arrangement  between  the 
malleus  and  incus. 

The  tiro  bony  parts  comprise  the  walls  of  the  cavity,  with  the 
mastoid  cells  and  Eustachian  tube;  also  the  ossicles  or  bones  of 
the  ear. 

The  soft  structnres  are:  (1)  the  ligaments  and  muscles  of  the 
little  ossicles,  (2)  the  mucous  membrane  of  the  tympanic  cavity,  (3) 
the  lining  of  the  Eustachian  tube,  and  (4)  the  membrana  tympani 
and  membrane  of  the  round  window. 

In  otitis  media  pus  may  cause  a  disintegration  of  the  mastoid 
cells,  from  which  it  frequently  extends  to  the  membranes  of  the 
brain. 


680 


PHYSIOLOGY. 


The  cavity  of  the  tympanum  forms  a  dilatation  added  to  the 
auditory  canal.  It  has  an  internal  wall,  an  external  Avail,  and  the 
Eustachian  tube.  The  mastoid  cells  communicate  by  a  large  orifice 
with  the  upper,  back  i)art  of  the  tympanum.  They  are  lined 
throughout  with  a  delicate  mucous  membrane. 

The  external  wall  is  occupied  in  its  greatest  extent  by  an  open- 
ing which  is  nearly  circular  and  closed  by  the  membrana  tympani. 
The  latter  is  semitransparent,  concave  externally  and  convex  inter- 
nally. To  its  inner  surface  is  attached  the  malkus,  one  of  the  three 
ear  ossicles. 


Fig.    .309. — Left   Tympanum   and   Auditory   Ossicles.      (Lanrois.) 

A.O.,    External   meatus.  .1/,    Membrana   tympani,    which   is   attached   to   the 

handle    of    the    malleus    (n)  and    near   its   short    process    (p).      h.    Head    of    the 

malleus.     «,   Incus.     K,    Its  short  process,   with   its   ligament.      /,   Long   process. 
8,  stapes. 


The  internal  ivall  is  convex  and  has  in  its  central  portion  a 
tubercle  known  as  the  promontory.  Its  base  corresponds  to  the 
origin  of  the  cochlea.  The  most  prominent  of  the  grooves  upon  its 
surface  marks  the  position  of  the  nerve  of  Jacohson. 

Above  the  promonotory  is  found  the  oval  windoir.  Its  shape  is 
really  reniform;   it  leads  to  the  vestibule. 

The  round  window  is  situated  Just  beneatli  the  oval  window.  It 
is  closed  by  a  membrane. 

The  ossicles,  which  form  an  articulated  chain,  reach  from  the 


THE  SENSE  OF  HEARING. 


681 


membrana  t3'mpani  to  the  oval  window.  In  number  they  are  three: 
the  malleus,  or  mallet;  the  incus,  or  anvil;  and  the  stapes,  or  stirrup. 
The  three  ossicles  form  a  chain  suspended  across  the  cavity  of  the 
tympanum.  The  handle  of  the  malleus  is  inserted  into  the  tym- 
panic membrane;  the  base  of  the  stirrup  is  applied  to  the  oval  win- 
dow. Between  these  two  ossicles  is  suspended  the  incus.  The 
ossicles  have  joints  w^hich  are  lined  wdth  synovial  membrane;  there 
are  present  suitable  ligaments. 

The  mucous  membrane  of  the  tympanum  is  very  thin,  and  either 
white  or  rose-colored.     It  envelops  the  chain  of  ossicles. 


Fig.  310. — Scheme  of  the  Organ  of  Hearing.  (LuVXBOls.) 
AG,  External  auditory  meatus.  T,  Tympanic  membrane.  A",  Malleus  with 
Its  head  (70,  short  process  (Uf),  and  handle  (?«)•  «,  Incus,  with  its  short 
process  (j-)  and  long  process;  the  latter  Is  united  to  the  stapes  (.s).  P,  Middle 
ear.  o.  Oval  window,  r.  Round  windov?.  x,  Beginning  of  the  lamina  spiralis 
of  the  cochlea,  pt.  Its  scala  tympani.  vt.  Its  scala  vestibuli.  V,  Vestibule. 
»Sf,  Saccule.  U,  Tubercle.  H,  Semicircular  canals.  TE,  Eustachian  tube.  The 
long  arrow  indicates  the  line  of  traction  of  the  tensor  tympani;  the  short 
curved  one  that  of  the  stapedius. 

The  Eustachian  tube  is  composed  of  a  bony  and  a  cartilaginous 
part.  The  canal  opens  at  the  anterior  upper  part  of  the  tympanum; 
its  pharyngeal  orifice  is  situated  ten  millimeters  behind  the  posterior 
extremity  of  the  nasal  fossa. 

The  Bony  Labyrinth,  or  Internal  Ear. — This  structure  is 
imbedded  within  the  substance  of  the  petrous  portion  of  the  tem- 
poral bone.  Its  long  axis  lies  in  a  position  parallel  with  that  of  the 
bone.  The  labyrinth  is  composed  of  three  portions:  vestibule,  semi- 
circular canals,  and  cochlea. 


682  PHYSIOLOGY. 

The  vcdihule  is  iin  oval,  irregular  cavity,  l.ying  between  tlie  tym- 
paniini  and  tlic  bottom  of  the  internal  anditory  meatus.  The  .semi- 
circular canals  open  from  it  posteriorly  and  the  cochlea  opens  from 
it  anteriorly.  Through  its  outer  wall  it  communicates  with  the  tym- 
panum by  the  oval  window.  The  fovea  heniispherica  and  fovea  hemi- 
elliptica  are  two  depressions  upon  the  inner  and  superior  walls  of 
the  vestibule,  respectively.  They  are  pierced  by  numerous  fora- 
mina; through  the  former  pass  the  filaments  of  the  cochlear  branch 
of  the  auditory  nerve ;  through  the  latter  foramina  pass  the  branches 
of  the  vestibular  branch.  Through  the  latter  also  pass  small  veins 
which  communicate  with  the  inferior  petrosal  sinus. 

The  semicircular  canals  are  three  in  number.  They  are  located 
above  the  inner  and  back  part  of  the  tympanum.  From  their  loca- 
tion they  are  named  superior,  posterior,  and  external.  The  canals  lie 
in  three  distinct  planes:  the  first  two  are  vertical,  but  nearly  at 
right  angles  to  one  another;   the  last  is  horizontal. 

Each  canal  is  rather  more  than  half  of  a  circle,  and  fonns  at 
one  extremity  a  dilatation  called  the  ampulla.  The  canals  communi- 
cate with  the  vestibule  by  five  openings,  one  of  which  belongs  to  both 
the  superior  and  posterior  canal. 

The  interior  of  the  vestibule  and  semicircular  canals  is  lined 
with  a  delicate  membrane.  The  cavity  formed  by  this  membrane 
contains  a  fluid  of  serous  nature.  It  is  known  as  the  perih/mph,  by 
reason  of  its  surrounding  a  secondary  structure,  the  labyrinth.  This 
last  structure  consists  of  a  pair  of  saccules  in  the  vestibule,  and  three 
semicircular  saccules  whose  form  is  the  same  as  the  osseous  canals 
containing  them.  This  membranous  labyrinth  comprising  the  sac- 
cules just  mentioned  itself  contains  a  serous  fluid,  the  endolymph. 

The  inner  portion  of  the  bony  labyrinth  is  the  cochlea :  so  named 
from  its  resemblance  to  a  shell.  Its  base  is  attached  to  the  internal 
auditory  meatus,  while  its  apex  is  directed  forward  and  outward. 
The  axis  of  the  cochlea  is  nearly  at  right  angles  to  that  of  the 
petrous  portion  of  the  temporal  bone  in  which  it  lies.  The  cochlea 
is  a  tube  of  bone  wound  around  a  central  axis,  each  turn  successively 
rising.  This  bony  tube  is  about  one  and  one-half  inches  long.  Its 
beginning  is  connected  with  the  fore  part  of  the  vestibule  to  produce 
the  promontory  of  the  tympanum;  it  ends  in  a  closed  extremity 
called  the  infundihulum.  The  central  axis  just  spoken  of  is  termed 
the  modiolus.     The  apex  of  the  cochlea  is  often  called  the  cupola. 

The  bony  canal  is  divided  into  two  passages,  or  scalce,  by  a 
septum    known    as    the    lamina   spiralis,    which    projects    from    the 


THE  SENSE  OF  HEARING. 


683 


modiolus.  The  two  scalse  commuincate  with  one  another  only  at 
the  top  of  the  cochlea,  by  an  opening:  the  hiatus,  or  helicotrema. 
That  portion  of  the  cochlear  canal  that  is  above  the  septum  termi- 
nates in  the  vestibule;  hence  scala  ■vestibuli.  The  lower  portion 
opens  into  the  tympanum  through  the  round  window;  hence  scala 
tympani. 

The  membranous  portion  of  the  septum,  or  lamina  spiralis,  con- 
sists of  two  layers:  The  superior  layer  is  the  membrane  of  Corti,  or 
membran-a  tedoria;  the  other  is  the  membrana  basilaris.  These  two 
membranes  are  placed  parallel  with  one  another  to  contain  between 
them  the  orga7i  of  Corti.  The  latter  rests  upon  the  basilar  mem- 
])rane. 


Fig.  311. — Scheme  of  the  Labyrinth  and  Terminations  of  the  Auditory 
Nerve.      (Landois.) 

I.  Transverse  section  of  a  turn  of  the  cochlea. 

II.  Ampulla  of  a  semicircular  canal,     a,  p,  Auditory  cells,     p,  Cell  provided 
with  a  fine  hair.     T,  Otoliths. 

III.  Scheme  of  the  human  labyrinth. 

IV.  Scheme  of  a  bird's  labyrinth. 

V.  Scheme  of  a  fish's  labyrinth. 

The  bony  portion  of  the  septum  has,  upon  its  superior  external 
surface,  a  denticulated,  cartilaginous  substance  called  the  lamina  den- 
ticulata.  From  the  superior  surface  of  the  lamina  spiralis,  and 
internal  to  the  lamina  denticulata,  exists  a  delicate  membrane,  the 
membrane  of  Beissner.  This  membrane  divides  the  scala  vestibuli 
into  two  passageways,  one  of  which  is  the  ductus  coclilearis.  It  con- 
tains the  essential  portion  of  the  auditory  apparatus  of  the  cochlea : 
the  organ  of  Corti.     It  forms  part  of  the  membranous  labyrinth. 

The  membranous  labyrinth  is  a  closed  sac  consisting  of  semi- 
circular canals,  a  vestibular  portion,  and  the  membranous  part  of 


684 


PHYSIOLOGY. 


Ihc  lamina  spiralis.  The  vestibular  portion  consists  of  an  expanded 
body,  the  ulriele,  and  a  smaller  body,  the  saccule.  Within  these  com- 
partments are  two  calcareous  bodies:  the  oiolilhs.  The  vestibidar 
filaments  of  the  cochlear  nerve  are  distributed  to  the  ampullge, 
utricle,  and  saccule.  In  the  first  the  fi])ers  terminate  in  elevations 
called  cristce  acusticw ;  in  the  last  two  they  end  as  oval  plates, — 
maculce, — colored  by  yellow  pigment. 

Organ   of   Corti. — The   organ   of   Corti  contains   the   following 
elements : — 


Sctymv-       „„CT 


aa^a^^ivfea 


Fig.  312. — Section  through  the  Uncoiled  Cochlea  (I)  and  througli 
the  Terminal  Nerve  Apparatus  of  the  Cochlea  (II).  (Munk,  after 
Hensen.) 

I.  Fr.,  Round  window.     H,  Helicotrema.     »S<.,  Stapes. 

II.  IS,  Huschke's  process,  h',  Basilar  membrane,  e,  Corti's  arch,  g,  Sup- 
porting cells,  h,  Cylindrical  cells,  i,  Deiters's  hair-cells,  c,  Membrana  tec- 
toria.    n,  Nerve-fibers.    «',  NonmeduUated  nerve-fibers. 

1.  Arches  of  Corti. — They  are  formed  of  an  internal  and  external 
pillar  whose  pedestals  rest  upon  the  basilar  membrane.  The  arches 
intercept  the  canal  of  Corti. 

2.  Internal  Auditory  Cells. — Inward  from  the  internal  pillar  of 
Corti  is  found  a  layer  of  auditory  cells.  These  cells  contain  nuclei, 
while  their  superior  extremities  terminate  in  a  plateau  having  long 
ciliated  prolongations;   their  inferior  extremities  are  in  relation  with 


THE  SENSE  OF  HEARING. 


685 


the   basilar   membrane   and   axis-cylinder   of    the    terminal   cochlear 
branches  of  the  auditory  nerve. 

3.  A  Granular  Layer  composed  of  rounded  cells. 

4.  Cells  in  the  sulcus  spiralis  which  are  cubical  in  shape. 

5.  The  External  Auditory  Cells,  whose  structure  and  arrange- 
ment are  very  similar  to  the  internal  cells  just  mentioned. 

6.  The  Cells  of  Deiters,  Hensen,  and  Claudius,  which  make  a 
prominence  upon  the  interior  of  the  cochlear  canal. 


Fig.  313. — Section  of  the  Ductus  Cochlearis  and  the  Organ  of  Corti. 
(After  Landois.) 

N,  Cochlear  nerve.  K,  Inner,  and  P,  outer,  hair-cells,  n.  Nerve-fibrils 
terminating  in  P.  a,  a.  Supporting  cells.  (7,  Cells  in  the  sulcus  spiralis,  z, 
Inner  rod  of  Corti.  Mb,  Corti,  membrane  of  Corti,  or  the  membrana  tectoria. 
o,  The  membrana  reticularis.  H,  G,  Cells  filling  up  the  space  near  the  outer 
wall. 

7.  Reticular  Mcmhrane. — The  membrana  reticularis  is  formed 
i)y  the  superior  extremity  of  the  cells  of  Deiters.  It  possesses  lacunae 
which  allow  the  passage  of  cilia  of  the  cells. 

8.  The  Memhrane  of  Corti,  or  membrana  tectoria,  is  a  soft,  thick 
membrane  which  covers  the  spiral  groove  and  organ  of  Corti.  Be- 
neath it  adheres  to  the  cilia  of  the  auditory  cells. 

Auditory  Nerve. — The  auditory  nerve  consists  of  two  ]iai'ts:  the 
cochlear,  the  hearing  part,  and  the  vestibular,  the  tonus  part.  The 
cochlear  part  arises  in  the  spiral  ganglion  of  the  cochlea,  and,  like  a 
posterior  root  ganglion,  sends  a  branch  to  the  auditory  cells  in  the 


686 


PHYSIOLOGY. 


organ  of  Corti  and  a  central  branch  to  the  cochlear  nucleus  in  the 
medulla.  The  cochlear  nucleus  consists  of  two  parts :  the  accessory 
nucleus  and  the  tuberculum  acusticum.  Hence  the  first  neuron  ex- 
tends from  the  spiral  ganglion  to  the  cochlear  nucleus;  then  the 
two   divisions   of  the   cochlear   nucleus — the   accessory  nucleus   and 


NVI      C^EVE. 


Oc  M. 


CocU.n. 


Fig.   314. — Connections  of  Coclilea  with   Central   Nervons   System. 

(Paton.) 

Coch.R,  Cochlear  root  of  eighth  nerve.  N.Acr,  Tuberculum  acusticum  and 
nucleus  accessorius  sending  fibers  to  the  cerebrum  (C.B.)  and  to  oculo-motor 
mechanism  {N.VI.). 


tuberculum  acusticum — send  out  neuraxons  to  the  superior  olive; 
here  they  are  second  neurons.  The  superior  olive  sends  out  neuraxons 
to  the  lateral  fillet;  here  the  third  neuraxons  make  up  chiefly  the 
lateral-fillet  fibers.  These  go  to  the  posterior  corpora  quadrigemina 
and  finally  are  connected  with  the  seat  of  hearing  in  the  first  tern-, 
poral  convolution. 

The  vestibular  root  arises  in  Scarpa's  ganglion-cells  of  the  laby- 
rinth and  goes  to  the  vestibular  nucleus. 


THE  SENSE  OF  HEARING. 


687 


The  vestibular  nucleus  is  composed  of  the  medial,  the  lateral, 
or  Deiters's,  the  superior,  or  Bechterew's,  and  the  nucleus  of  the 
descending  root.  There  are  connections  between  the  nucleus  of 
Deiters  and  the  nucleus  fastigii  of  the  cerebellum.     Deiters's  nucleus 


£Y£. 


CCLLS    a 
Ant  Hotn. 


Fig.  'M'). — Connections  of  Semi-circular  Canals  with  Central  Nervous 
System.      (  Paton.  ) 

Ves.R,  Vestibular  root  of  eighth  nerve  sending  fibers  to  C.B  (cerebrum)  and 
C.B.L  (cerebellum)  downwards  to  center  in  medulla  oblongata  (Med),  and  to 
Deiters's  nucleus  (.V.DciO.  from  which  fibers  pass  to  oculo-motor  mechanism 
(N.Vi)  and  to  center  in  the  anterior  horn  of  the  spinal  cord. 

is  connected  with  the  vestibulo-spinal  tract  which  runs  down  the  cord 
to  the  anterior  horns.  Fibers  from  the  cerebellar  nuclei  go  by  the 
superior  cerebellar  peduncle  and  the  red  nucleus,  and  end  in  the 


688  PHYSIOLOGY. 

cortex  of  the  parietal  and  central  convolutions.  Some  fibers  from 
the  nucleus  of  Deiters  and  of  Bechtcrew  go  by  the  posterior  longi- 
tudinal bundle  to  the  nuclei  of  the  motor  nerves  of  the  eye.  (See 
equilibratory  center  of  Mills.) 

The  cochlear  nerve  is  the  nerve  concerned  in  hearing. 

The  vestibular  nerve  is  the  nerve  concerned  in  equilibration.  It 
docs  not  have  anything  to  do  with  hearing. 

Memhrana  Tympani. — The  membrana  tympani  is  an  elastic, 
very  vascular  membrane,  which  protects  the  delicate  organs  of  the 
middle  ear  against  the  action  of  cold  coming  in-  from  the  external 
ear.  It  is  also  specially  endowed  with  a  specific  sensibility  for  the 
contact  of  special  agents,  as  the  scratchings  of  an  insect  on  its  surface 
cause  a  peculiar  auditory  sensation.  The  membrana  tympani  is  of 
variable  size,  according  to  the  species  of  animal,  and  is  adapted  to 
receive  low  and  high  sounds.  It  is  of  circular  form,  and  attached 
by  its  borders  upon  a  bony  circle,  the  tympanic  circle.  Its  direction 
is  peculiar.  It  cuts  obliquely  the  axis  of  the  external  auditory 
meatus  and  this  obliquity  is  favorable  to  the  impact  of  sound-waves. 
It  is  depressed  and  becomes  prominent  in  the  middle,  having  the 
arrangement  of  a  depressed  cone.  Under  the  shock  of  sound-waves 
the  membrana  tympani  vibrates  for  all  sounds  in  the  range  of  per- 
ceptible sounds.  Its  vibration  can  be  measured  by  a  water  mano- 
meter inserted  into  the  external  auditory  canal. 

Accommodation  of  Memhrana  Tympani. — Since  the  membrana 
tympani  vibrates  in  unison  with  all  the  external  sounds  which  strike 
it,  it  is  inferrable  that  there  is  a  means  capable  of  regulating  the 
tension  of  this  membrane.  The  shape  of  the  tympanic  membrane 
is  peculiarly  adapted  for  transforming  weak  movements  of  wide 
amplitude  into  strong  ones  of  wide  compass.  For  it  is  not  simply  a 
depressed  cone,  but  the  radii  are  slightly  curved  with  the  convexity 
outward,  a  shape  mainly  caused  by  the  elastic  fibers  maintaining  a 
tension  on  its  inner  surface,  these  being  most  numerous  toward  the 
circumference.  The  principal  regulator  of  the  tension  is  the  tensor 
tympani.  The  membrane  of  the  tympanum  has  no  definite  funda- 
,  mental  tone ;  it  vibrates  indifferently  to  every  sound.  The  mem- 
brana tympani  is  tense  for  high  sounds  and  relaxed  for  low  sounds, 
but  these  changes  in  tension  are  chiefly  for  the  intensity  of  sound 
rather  than  their  height,  so  as  to  offer  a  resistance  to  the  shock  of 
sound-waves  and  obviate  the  effect  of  this  shock  upon  the  deep  and 
delicate  structure  of  the  ear. 

The  adherence  of  the  membrana  tympani  to  the  handle  of  the 


THE  SENSE  OF  HEARING.  689 

malleus,  which  follows  its  movements,  causes  its  vibrations  to  meet 
with  considerable  resistance.  This  diminishes  the  intensity  of  the 
vibrations,  and  prevents  also  the  continued  vibration  of  the  mem- 
brane after  an  external  vibration  has  ceased,  so  that  a  sound  is  not 
heard  much  longer  than  the  moment  when  the  exciting  cause  ceases. 
The  tensor  tympani  at  its  base  arises  from  the  apex  of  the  petrous 
portion  of  the  temporal  bone  and  the  cartilage  of  the  Eustachian 
tube,  and  is  inserted  into  the  malleus  near  its  root.  The  membrana 
tympani  has  the  handle  of  the  malleus  inserted  into  its  layers;  and 
as  the  malleus  and  incus  move  around  an  axis  passing  through  the 
necK  of  the  malleus  from  before  backward,  the  action  of  the  tensor 
tympani  is  to  pull  the  membrana  tympani  inwards  toward  the 
tympanic  cavity  in  the  form  of  a  funnel,  the  meridians  of  which 
are  not  straight,  but  curved  with  the  convexity  outwards.  This 
making  tense  and  relaxing  the  membrana  tympani  is  a  kind  of 
accommodating  apparatus  for  receiving  and  transmitting  sounds 
of  different  pitch.  With  different  tensions  it  will  respond  more 
readily  to  sounds  of  one  pitch  than  to  sounds  of  another. 

The  tensor  tympani  receives  its  motor  fibers  from  the  fifth  by 
the  otic  ganglion,  and  its  movements  are  purely  reflex. 

The  stapedius  muscle  is  innervated  by  the  facial  and  exercises 
an  antagonistic  action  to  the  tensor  tympani.  The  stapedius  draws 
the  stapes  outward,  whilst  the  tensor  tympani  tends  to  press  the 
stapes  into  the  oval  window.  The  two  antagonistic  muscles  are  able 
to  comliine  in  such  a  manner  as  to  modify  the  length  of  the  chain 
of  ossicles,  and  give  an  amplitude  variable  to  the  vibrations. 

Hensen  has  proved  that  these  muscles  are  reflexly  kept  in  a  state 
of  adjustment  by  the  pitch  of  sound. 

Transmission  of  Sound  Waves  in  the  Middle  Ear. — The  normal 
and  regular  means  of  transmission  of  sounds  is  by  the  chain  of  ossi- 
cles, but  it  can  take  place  by  the  air  in  the  cavity  of  the  tympanum, 
or  by  the  bones  of  the  skull. 

The  ossicles  of  the  middle  ear  form,  by  the  articulations  which 
unite  them,  a  broken  but  rigid  chain  between  the  membrana  tympani 
and  the  oval  window.  This  chain  of  bones  is  not  always  in  the  same 
state,  for  the  combined  action  of  the  two  muscles  modifies  the  length 
and  rigidity  of  the  chain.  Pollitzer,  by  means  of  very  fine  pens,  has 
been  able  to  register  the  movements  of  the  bones.  In  rarefaction 
of  the  air  in  the  auditor}^  meatus,  as  with  the  pneumatic  speculum, 
there  is  no  clanger  of  pulling  the  stapes  out  of  the  oval  window,  for 
the  incus  only  follows  the  malleus  for  a  certain  distance,  the  latter 


690  PHYSIOLOGY. 

completing  its  motion  by  gliding  in  the  joint.  The  destruction  of  the 
chain  of  bones  does  not  necessarily  cause  deafness,  any  more  than 
perforation  of  the  membrana  tympani,  as  long  as  the  stapes  is  pre- 
served. If  the  stapes  is  torn  out  there  is  deafness,  because  the  peri- 
lymph escapes  into  the  middle  ear  and  it  is  not  able  to  transmit 
sound-waves  to  the  membranous  labyrinth. 

The  bones  of  the  head  also  conduct  sounds,  as  is  easily  proved 
by  closing  the  ears  with  your  fingers  and  putting  a  watch  between 
the  teeth.  The  intervention  of  the  bones  of  the  skull  in  the  trans- 
mission of  sounds  is  made  use  of  in  the  audiphone  for  the  deaf, 
where  a  rod,  which  terminates  in  a  large  disk  spread  out  to  receive 
sounds,  is  held  between  the  teeth. 

Transmission  of  Sounds  by  the  Air  in  the  Middle  Ear. — In  the 
normal  state  the  air  enclosed  in  the  tympanic  cavity  plays  an  insig- 
nificant part  in  the  transmission  of  sound-waves,  but  its  interven- 
tion is  inevitable  when  the  chain  of  ossicles  has  been  destroyed.  It 
is  probable  that  it  conveys  the  sound  to  the  round  window. 

Eustachian  Tube. — The  air  enclosed  in  the  middle  ear  is  con- 
stantly kept  in  an  equilibrium  of  pressure  with  the  external  air  by 
the  intermittent  patency  of  the  Eustachian  tube,  which  extends  be- 
tween the  cavity  of  the  tympanum  and  the  pharynx.  The  Eustachian 
tube  is  opened  in  each  act  of  deglutition,  by  the  salpingo-pharyngeus 
and  the  dilator  tubal  muscles.  If  the  air  is  enclosed  in  the  tympanic 
cavity,  the  oxygen  goes  to  the  blood  and  the  carbon  dioxide  is  given 
off,  but  the  amount  of  carbonic  acid  given  out  is  less  than  the  amount 
of  oxygen  removed,  so  that  the  total  quantity  of  gases  in  the  tym- 
panic cavity  is  reduced,  the  air  is  rarefied,  and  the  membrana  tym- 
pani, on  account  of  the  vacuum,  presses  upon  the  chain  of  ossicles, 
which  are  immobilized  and  do  not  readily  transmit  any  vibrations. 
By  a  forced  expiration,  the  oral  and  nasal  cavities  being  closed,  fol- 
lowed by  an  act  of  deglutition,  air  may  be  driven  into  the  tympanic 
cavity  and  a  crackling  noise  will  be  heard.  This  is  Valsalva's  positive 
experiment.  A  forced  inspiration  accompanied  by  deglutition  will 
draw  air  from  the  cavity,  again  causing  a  crackling  noise,  the  nega- 
tive experiment  of  Valsalva.  In  the  positive  experiment  of  Valsalva 
the  membrana  tympani  bulges  outward ;  in  the  negative  experiment 
it  bulges  inward ;  and  in  both,  from  the  extreme  tension  of  the  mem- 
brane, there  is  a  partial  deafness  for  high-pitched  sounds. 

Permanent  closure  of  the  Eustachian  tube  by  catarrhal  condi- 
tions is  the  most  frequent  cause  of  deafness.  Closure  of  the  tube, 
except  in  deglutition,  is  necessary  for  the  transmission  of  sound-waves 


THE  SENSE  OF  HEARING. 


691 


in  tlie  middle  ear.  Deglutitions  periodically  open  the  Eustachian  tube 
and  form  an  auxiliary  function  to  that  of  hearing.  These  acts  follow 
each  other  at  short  intervals  and  are  repeated  often  during  the  day, 
even  during  sleep. 

In  a  deep  mine  where  the  atmosphere  is  considerably  more  dense 
than  that  on  the  surface,  the  uninitiated  is  instructed  to  swallow 
every  few  minutes.  By  so  doing  he  maintains  an  equable  pressure 
upon  both  sides  of  the  membrana  tympani. 

The  secretory  nerve  of  the  submaxillary  gland  is  the  chorda 
tympani,  which  passes  through  the  middle  ear  and  may  be  considered 
as  a  proof  of  the  functional  unity  which  belongs  to  the  salivary  secre- 
tion and  hearing. 


Fig.   316. — I.  The  Mechanics   of   the   Auditory   Ossicles.      (After  Helm- 
HOLTZ.)     II.  Section  of  the  Middle  Ear.     (Munk,  after  Hensen.) 

I.  a.  Malleus,     h.  Incus,     am,  Long  process  of  incus,     s,  Stapes.     The  arrows 
show  the  direction  of  motion. 

II.  G,    E.^ternal   auditory  canal.     M.t.,   Membrana   tympani.      C,    Tympanum. 
H,  Malleus.    L.S.,  Superior  ligament.    S,  Stapes. 

Movements  of  the  Osskles. — To  the  tympanic  membrane  is  at- 
tached the  handle  of  the  malleus,  whilst  projecting  above  the  edge 
of  the  membrane,  into  the  tjTnpanic  cavity,  is  the  head  of  the  bone. 
Helmholtz  states  that  the  malleus-incus  articulation,  in  its  action, 
may  be  compared  with  the  points  of  the  Breguet  watch-keys,  which 
have  rows  of  interlocking  teeth  which  offer  scarcely  any  resistance 
to  revolution  in  one  direction,  but  allow  no  revolution  in  the  other. 
Hence,  when  the  handle  of  the  malleus  moves  inward  toward  the 
tympanic  cavity,  the  incus  and  its  long  process,  which  is  parallel  with 


692  PHYSIOLOGY. 

the  handle  of  the  malleus,  also  passes  inward,  from  the  fact  that  the 
head  of  the  malleus  pulls  the  articulating  surface  of  the  incus  out- 
ward. The  long-  j^rocess  of  the  incus  and  the  handle  of  the  malleus 
vibrate  in  the  same  direction.  When  the  long  process  of  the  incus 
moves  inwaj-d  it  gives  an  impression  to  the  stapes,  with  which  it 
articulates  almost  at  right  angles.  The  stapes  cannot  he  torn  out 
of  the  oval  window  by  the  Sigle  pneumatic  speculum  when  the  tym- 
panic membrane  is  drawn  outward,  as  the  incus  only  follows  the 
malleus  for  a  certain  distance,  the  malleus  sliding  in  the  joint  to 
complete  its  motion.  The  malleus  and  incus  are  fixed  by  ligaments 
in  such  a  way  that  motion  is  only  possible  in  to-and-fro  vibrations 
around  the  so-called  axis  of  rotation,  one  end  of  which  is  found  at 
the  origin  of  the  anterior  part  of  the  anterior  ligament  of  the 
malleus,  and  the  other  end  in  the  short  process  of  the  incus.  The 
ossicles  of  the  ear  act  like  a  compound  lever;  the  short  process  of 
the  incus  is  the  fulcrum ;  the  power  is  applied  to  the  umbo,  in  which 
the  handle  of  the  malleus  ends;  and  the  resistance  is  the  base  of 
the  stapes.  The  length  of  the  handle  below  the  axis  of  the  malleus 
is  one  and  one-half  times  that  of  the  head  above  the  axis.  But  the 
range  of  excursion  is  only  two-thirds  that  of  the  handle  and  drum- 
head, whilst  the  power  of  movement  of  the  head  of  the  malleus  will 
be  one  and  one-half  times  more  than  that  of  the  handle.  By  this 
means,  according  to  Helmholtz,  vibrations  are  diminished  in  extent 
but  increased  in  force.  The  chain  of  ossicles  vibrates  as  a  whole, 
and  not  by  molecular  vibration.  The  tympanic  membrane  is  twenty 
times  the  size  of  the  oval  window;  hence  the  movement  of  the  mem- 
brane of  the  oval  window  is  smaller  in  extent,  but  about  thirty  times 
greater  in  power.  When  sound  impinges  against  the  tympanum,  the 
tympanic  membrane  moves  inward  with  the  attached  handle  of  the 
malleus,  and  the  head  of  the  malleus  moves  outward.  The  incus  fol- 
lows these  movements ;  the  body  of  the  incus  swings  outward  and  the 
long  process  moves  inward,  which  pushes  the  stapes  into  the  oval 
window. 

Thus  the  ossicles  and  the  fluid  in  the  labyrinth  do  not  form  a 
mass  vibrating  independently,  but  as  one  body. 

Tensor  Tympani. — The  tensor  tympani  reflex  has  its  sensory 
nerves  from  the  trigeminus  and  its  motor  nerve  from  the  same  source. 
When  one  tensor  tympani  contracts,  the  tensor  of  the  opposite  side 
also  contracts. 

In  rare  cases  the  tensor  tympani  is  under  the  control  of  the  will. 


THE  SENSE  OF  HEARING.  693 

A  man  who  is  absolutely  deaf  in  one  ear  has  great  difficulty  in 
recognizing  the  direction  of  sound. 

It  will  be  recalled  by  the  student  that  all  of  the  spaces  and  com- 
partments of  the  internal  ear,  or  labyrinth,  are  filled  with  peril}-mph, 
and  that  in  this  fluid  float  saccules  containing  endolymph  fluid.  So 
intimately  are  all  of  the  parts  of  the  labyrinth  associated  that  any 
vibration  of  its  contained  fluid  at  one  part  is  promptly  propagated 
to  every  other  portion.  The  vibrations  of  the  fluid  striking  upon 
the  tiny  nerve-filaments  act  as  stimulants  whose  impressions  are 
carried  to  the  center  of  hearing,  where  the  impressions  are  recog- 
nized as  sound. 

To  epitomize:  The  sonorous  waves  collected  by  the  auricle  to 
pass  through  the  external  auditory  meatus  and  along  its  canal  strike 
the  surface  of  the  membrane  of  the  tympanum.  It  becomes  tense, 
vibrates  in  unison,  and  then  communicates  its  vibrations  through  the 
ossicles  and  contained  air  in  the  tympanum  to  the  oval  window. 

From  here  the  vibrations  are  carried  over  the  vestibule,  semi- 
circular canals,  and  labyrinth  to  the  perflymph.  From  this  the  vibra- 
tions are  transmitted  through  the  membranous  walls  of  the  sacculus 
to  the  endolymph.  Vibrations  also  pass  from  the  vestibule  to  the 
scala  vestibuli  of  the  cochlea,  and,  through  the  helicotrema,  descend- 
ing the  scala  tympani,  end  as  an  impulse  against  the  membrane  of 
the  round  window. 

Most  of  the  organs  of  special  sense  contain  a  "specially  modi- 
fied epithelium"  for  the  reception  of  the  particular  kind  of  stimulus 
peculiar  to  each  other.  Xor  is  the  sense  of  hearing  different  from 
the  others.  It  also  has  its  tissues  representing  "specially  modified 
epithelium"  in  which  lie  the  terminal  filaments  of  the  auditory 
nerve.  These  tissues  are  so  constituted  that  they  receive  the  "waves 
of  sound"  which  generate  auditory  impulses  in  the  auditory  nerve. 
These  last,  when  conveyed  to  the  brain,  are  developed  into  auditory 
sensations. 

The  vibrations  of  elastic  bodies  produce  condensation  and  rai'e- 
faction  of  the  enveloping  atmosphere.  That  is,  there  are  developed 
waves  whose  particles  vibrate  longitudinally.  These  waves  are 
usually  spoken  of  as  sound-waves. 

iSTormally.  then,  the  auditory  nerve  may  be  stimulated  by  sonor- 
ous vibrations  which  set  into  motion  the  end-filaments  of  the  acous- 
tic nerve.  The  filaments  are  distributed  over  the  inner  surface  of 
the  membranous  labyrinth,  upon  the  membranous  expansions  of  the 
cochlea,  and  in  the  semicircular  canals.     The  excitement  of  the  fila- 


694  PHYSIOLOGY. 

meuts  is  really  mechanical  in  nature,  due  to  the  wavelike  motion  of 
the  serous  fluid  of  the  membranous  labyrinth. 

It  is  common  to  divide  auditory  stimuli  into  those  which  are 
caused  by  noises  and  those  caused  by  musical  sounds.  It  is  a  feature 
peculiar  to  musical  sounds  that  the  vibrations  which  form  them  are 
periodical  and  that  they  recur  at  regular  intervals.  When  neither 
of  these  two  conditions  is  present,  there  results  a  noise.  From  the 
sensory  impulses  to  which  the  several  vibrations  give  rise  are  gen- 
erated our  sensations  of  noise  or  of  sound. 

To  produce  a  sensation  certain  conditions  in  the  excitation  of 
the  auditory  nerve  are  necessary. 

The  sound-wave  must  exist  for  a  certain  length  of  time ;  it  must 
not  be  greater  than  ^/^^  nor  less  than  ^Aoooo  second.  In  the  piano 
the  lowest  base  (C,  33  vibrations)  and  the  highest  treble  (C,  422-i 
vibrations)  exist.  A  certain  number  of  impulses  must  be  made 
within  a  given  interval  of  time  to  excite  a  sensation  of  tone.  The 
lower  limit  is  about  30  vibrations,  the  upper  limit  about  40,000,  per 
second.  Visual  sensations  separated  by  less  than  a  tenth  of  a  second 
are  fused,  but  auditory  sensations  separated  by  V133  second  remain 
distinct. 

Theory  of  Hearing. — If  you  sing  a  note  into  a  piano,  the  cords 
of  the  piano  tuned  for  this  note  only  respond.  Now  the  basilar 
membrane  is  supposed,  like  a  harp,  to  represent  a  series  of  cords 
which,  like  the  piano-strings,  respond  to  the  sounds  striking  them. 
This  membrana  basilaris  is  striated  in  a  radiating  direction,  and 
these  striations  increase  as  it  ascends  toward  the  helicotrema.  Un- 
like the  harp,  the  cords  are  joined  together  by  their  edges;  but,  as 
they  are  stretched  only  in  a  radiating  direction,  they  can  vibrate  as 
though  they  were  separate  cords.  Now,  the  cords  are  very  short, 
being  at  most  not  over  ^/^^  iiich  in  length;  so  that  they  would  be 
expected  only  to  vibrate  for  high  sounds;  but  it  must  be  remem- 
bered that  these  cords  are  weighted  with  the  arches  and  cells  of 
Corti,  which  lower  their  sound.  Hence  we  have  a  series  of  cords  in 
the  basilar  membrane  vibrating  separately  to  musical  sounds.  We 
know  that  there  are  in  man  about  3000  arches  of  Corti,  and  as  at  least 
two  of  the  cords  correspond  to  an  arch  of  Corti,  we  have  6000  cords. 
Now,  the  scale  of  musical  sounds  extends  to  seven  octaves,  and  we 
have  400  arches  of  Corti  to  1  octave.  In  1  octave  there  are  13  semi- 
tones, and  we  have  66  cords  corresponding  to  a  semitone;  so  that 
we  have  sufficient  cords  to  vibrate  in  unison  with  all  possible  musical 
sounds. 


THE  SENSE  OF  HEARING. 


695 


When  the  sound-waves  vibrate  the  cells  of  Corti  they  make  the 
terminal  filaments  of  the  cochlear  nerve  vibrate,  because  they  are  in 
relation  with  the  cells  of  Corti.  The  analysis  of  sounds  takes  place 
in  the  brain. 

Binaural  Audition. — The  hearing  of  a  single  sound  with  both 
ears  may  be  due  to  habit  or  to  the  connection  in  the  nerve-centers 
of  the  fibers  connected  with  both  ears.  Undoubtedly  binaural  audi- 
tion facilitates  our  knowledge  of  the  direction  of  sound,  since  each 
ear  has  its  own  axis  and  direction. 


Fig.   317. — Schema  of  the  Semicircular   Canals,  the  Posterior  Part  of 
the'  Skull  Removed.     (Hedon,  after  Ewald.) 

In  the  plane  1  lies  the  anterior  canal.    In  the  plane  2  the  external  canal. 
In  the  plane  3  the  posterior  canal. 

We  combine  binauricular  audition,  just  as  we  judge  of  the  relief 
of  objects  in  binocular  vision  (stereoscopic  vision),  to  determine  the 
direction  of  sounds.  The  tympanic  membrane  may  be  looked  upon 
as  an  organ  of  pressure-sense  by  variations  of  air-pressure,  even 
when  sound-sensations  are  not  produced. 

A  blind  man  has  been  able  to  state  correctly  that  he  has  passed 
a  fence,  and  whether  it  be  of  solid  board  or  of  open  picket.  It  may 
be  stated  that  the  membrana  tympani  is  the  outward  organ  of  pressure- 
sense,  by  which  we  know  more  or  less  the  position  of  objects  inde- 
pendent of  the  sensations  of  sight  and  hearing.  The  air  is  in  endless 
movement,  and  its  waves,  striking  against  various  objects,  must  be 
impinged  against  the  drumhead  with  an  intensity  dependent  upon 
their  position  and  the  physical  properties  of  the  bodies  reflecting  it. 


696  PHYSIOLOGY. 

Auditory  Sounds. — All  auditory  sensations  are  immediately  re- 
ferred to  the  external  air.  When  your  head  is  immersed  in  water, 
then  the  auditory  sensations  are  not  projected  externally,  but  seem 
to  arise  in  the  ear. 

Auditory  Judgement. — The  auditory  sensations  inform  us  of  the 
nature,  distance,  and  relative  situation  of  bodies.  The  Judgments 
draw  their  exactness  from  associations  established  in  previous  ex- 
periences between  those  of  hearing  and  the  other  senses.  When  we 
hear  a  particular  instrument,  the  sensation  we  experience  calls  up  a 
picture  of  all  its  qualities  which,  from  our  past  experience,  we  know 
belong  to  that  instrument.     The  appreciation  of  the  distance  of  a 


"•?S!55a!!;LH|||lci«'(^ 


Fig.  318. — Semi-circular  Canals  on  Right  Side  Destroyed.  Com- 
mencing rotation  of  head  of  pigeon  about  five  days  after  the  operation. 
(After  EwALD. )  (From  Tigerstedt's  "Human  Pliysiology,'  copyright, 
1906,  by  D.  Appleton  and  Company.) 

body  by  its  sound  results  from  thousands  of  experiences  between  audi- 
tory impressions  of  that  body  and  the  visual  impressions.  The  auricle 
has  an  important  part  in  the  determination  of  the  direction  of 
sounds,  causing  an  inequality  of  impressions  which  strike  the  two 
ears. 

Semicircular  Canals. — The  semicircular  canals  are,  through  the 
vestibular  nerve  and  the  cerebellum,  the  most  important  agents  in 
the  preservation  of  equilibrium.  When  in  a  pigeon  the  horizontal 
canals  are  divided,  the  head  moves  from  left  to  right  and  from  right 
to  left,  with  nystagmus  and  a  tendency  to  revolve  on  its  vertical  axis. 
When  the  inferior  vertical  or  posterior  canals  are  divided,  the  head 
oscillates  from  front  to  rear;  the  animal  has  a  tendency  to  fall  back- 
ward.    A  section  of  the  superior  vertical  canal  causes  the  head  to 


THE  SENSE  OB  HEARING.  697 

oscillate  from  front  to  rear,  with  a  tendency  to  fall  forward.  A  sec- 
tion of  all  the  canals  is  followed  by  contortions  of  the  most  bizarre 
nature.  After  a  destruction  of  all  the  canals  the  animal  cannot  main- 
tain his  equilibrium. 

Similar  phenomena  have  been  observed  in  man  in  disease  of  the 
semicircular  canals,  known  as  Meniere's  vertigo.  In  the  fixed  position 
of  the  head  there  is  equilibrium,  hut  with  each  movement  the  vary- 
ing tension  of  the  liquid  in  the  ampulla  changes  and  irritates  the 
hair-cells. 

The  horizontal,  semicircular  canals  form  the  arc  of  a  circle,  with 
an  ampulla  at  each  end.  In  rotation  of  the  head  to  the  right,  the 
endolymph  in  the  ampulla  of  the  right  horizontal  canal  will  accumu- 


Fig.  319. — Twisting  of  the  Head  of  a  Pigeon  twenty  days  after 
removal  of  all  the  semi-circular  canals  on  the  right  side.  (Ewald, 
J.  R.)  (From  Tigerstedt's  "Human  Physiology,"  copyright,  1906,  by 
D.  Appleton  and  Company.) 

late  in  the  ampulla  because  the  membranous  canal  is  very  narrow. 
This  will  cause  a  high  pressure  in  the  ampulla. 

These  ampullae  and  canals  are,  then,  sensory  organs,  and  give  the 
animal  an  idea  of  the  position  of  his  head  in  space.  Now,  as  the  canals 
are  at  right  angles  to  each  other  according  to  the  three  dimensions  in 
space,  their  section  makes  the  animal  unable  to  know  the  position 
of  his  head  and  thus  produces  vertigo.  Cyon's  theory  that  the  semi- 
circular canals  give  us  a  series  of  unconscious  sensations  as  to  the 
position  of  our  heads  in  space,   (See  cerebellum.) 

Ewald  holds  that  all  the  muscles  of  the  body  are  kept  in  a  state  of 
tonus  by  means  of  the  semicircular  canals,  and  that  injury  to  them 
affects  those  muscles  whose  movements  are  most  delicate,  such  as 
those  of  the  eye  and  larynx.  The  loss  of  tonus  may  be  explained  for 
some  of  the  muscles  by  disturbances  in  the  reflex  arc  of  the  vestibular 
nerve,  Deiters's  nucleus,  and  the  vestibulo-spinal  tract.     Here  is  a 


698  PHYSIOLOGY. 

reflex  between  the  semicireiilar  canals  and  the  muscles  of  the  body 
innervated  by  the  anterior  horns  which  liave  the  vcstibulo-spinal 
tract  connected  with  thcni. 

The  fibers  from  Deitcrs's  nucleus  go  to  the  nuclei  of  the  motor 
nerves  of  the  eye  by  the  posterior  longitudinal  bundle;  hence  the 
nucleus  of  Deiters  may  be  a  reflex  center,  with  the  semicircular  canal 
on  one  side  and  the  fibers  from  Deiters's  nucleus  to  the  motor  nuclei 
for  the  eye-muscles  on  the  other  side.  Destruction  of  the  semicircular 
canals  would  thus  cause  loss  of  tonus  in  the  eye-muscles. 


Fig.  320. — Position  of  Pigeon's  Head  after  removal  of  all  the  semi- 
circular canals  on  both  sides.  (Ewald,  J.  R.)  (From  Tigerstedt's 
"Human  Physiology,"  copyright,   1906,  by  D.  Appleton  and  Company.) 

A  20-gram  lead  baU  fastened  to  beak  with  wax,  which  cannot  be  moved,  owing 
to  weakness  of  the  muscles  of  the  neck. 

TJtriculus  and  Sacculus. — The  utriculus  and  sacculus.  small  sacs, 
also  contain  hair-cells,  and  lying  among  them  are  the  otoliths,  con- 
sisting of  crystals  of  calcium  carbonate.  Breuer  states  that  these  sacs 
give  us  information  when  the  head  is  at  rest  and  when  it  is  making 
slow  rotary  movements.  Thus  they  aid  the  function  of  the  semicir- 
cular canals.  In  this  view,  the  otoliths  mechanically  stimulate  the 
hairs. 


CHAPTER  XIX. 

SPECIAL  SENSES  (Concluded.) 

VISION. 

Those  bodies  are  said  to  be  liniiinons  which  especially  affect  the 
organ  of  vision.  Some  are  luminous  in  themselves,  others  become 
so  by  reflection.  Since  there  is  no  direct  contact  between  the  visual 
apparatus  and  the  object  which  makes  the  impression,  and  since  the 
distance  which  separates  them  is  often  infinite,  it  is  impossible  not 
to  admit  the  existence  of  a  particular  intervening  agent  between  the 
center  of  radiation  and  the  eye.     This  agent  is  ether. 

How  Does  Light  Transmit  Itself? — The  accepted  theory  to-day 
with  regard  to  its  propagation  is  the  undulatory,  or  wave,  theory. 
Its  doctrines  make  light,  like  heat  and  sound,  a  mode  of  motion. 

A  luminous  body  is  one  whose  particles  are  in  a  state  of  vibration. 
That  they  may  give  rise  to  a  luminous  impression  it  is  necessary  that 
they  be  transmitted  to  the  eye.  Ordinarily  the  atmospheric  air  is  the 
usual  medium  for  the  transmission  of  the  vibrations  of  a  sounding 
body  to  our  ears.  However,  a  luminous  body  does  not  become  invisi- 
ble in  a  vacuum,  as  does  a  sounding  body  become  inaudible.  Hence, 
there  must  be  supposed  the  existence  of  a  highly  elastic  medium  that 
pervades  all  spaces  and  all  bodies.  To  this  especial  medium  luminous 
bodies  communicate  their  vibrations  to  be  transmitted  with  enormous 
velocity.     This  medium  is  known  to  physicists  as  ether. 

Suppose  a  luminous  body  isolated  in  a  gas  or  suspended  in  a 
vacuum;  it  will  be  visible  in  all  directions.  Imagine,  also,  a  point  of 
space  lighted  up  by  its  radiations.  The  line  which  joins  this  point 
to  one  of  the  elements  of  the  luminous  body  represents  the  direction  of 
a  ray  of  light.  So  long  as  no  obstruction  intervenes  the  ray  of  light 
pursues  an  even,  straight  course.  Should,  however,  a  mirror  inter- 
cept its  path,  the  greater  portion  of  it  will  be  bent  out  of  its  regular 
course.  That  is,  it  is  reflected.  In  all  cases  of  reflection  it  is  well  to 
remember  that  "the  angle  of  reflection  always  equals  the  angle  of  in- 
cidence." 

Again,  the  passage  of  light  through  transparent  media  of  various 
densities  presents  peculiarities:  its  straight  course  is  modified — 
broken.  To  convey  a  conception  of  this  phenomenon  the  term  re- 
fraction is  used. 

(699)  , 


700  PHYSIOLOGY. 

The  organ  of  siglit,  the  eye,  is  constructed  upon  the  principles  of 
the  camera  obscura.  In  the  latter  the  collecting  lens  unites  the  light 
impressions  at  the  back  of  the  apparatus  to  form  upon  the  ground- 
glass  plate  a  diminished  and  reversed  image  of  external  objects. 

Structure. — The  (!ye  is  composed  of  three  concentric  coats  (scle- 
rotic, choroid,  and  retina),  the  aqueous  and  vitreous  humors  and  the 
crystalline  lens. 


Fig.  321. — Diagram  of  a  Horizontal  Section  through  the  Human  Eye. 

(Yeo.) 

1,  Cornea.  2,  Sclerotic.  3,  Choroid.  4,  Ciliary  processes.  5,  Suspensory 
ligament  of  lens.  6,  So-called  posterior  chamber  between  iris  and  lens.  7, 
Iris.  8,  Optic  nerve.  8',  Entrance  of  cerebral  artery  of  retina.  8",  Central 
depression  of  retina,  or  yellow  spot.  9,  Anterior  limit  of  retina.  10,  Hyaline 
membrane.  11,  Aqueous  chamber.  12,  Crystalline  lens.  13,  Vitreous  humor. 
14,  Circular  venous  sinus  which  lies  around  the  cornea,  a-a,  Antero-posterior 
axis  of  bulb.     6-6,  Transverse  axis  of  bulb. 

The  first,  or  outside,  coat  of  tlie  eye  is  opaque  in  all  of  its  parts 
except  a  small  anterior  segment.  This  area,  which  is  about  one-sixth 
of  the  entire  circumference,  is  perfectly  transparent.  The  dense, 
opaque  part  is  known  as  the  sclerotic;  the  transparent  portion  is  the 
cornea,  which  is  the  most  anterior  portion  of  the  sclerotic. 

The  sclerotic  is  thickest  behind,  in  the  neighborhood  of  the  part 
pierced  by  the  optic  nerve,  which  is  placed  about  a  tenth  of  an  inch 
inside  of  the  antero-posterior  axis.     The  sclerotic  thins  a  little  as  it 


VISION. 


701 


passes  forward,  and  is  weakest  about  two  lines  from  the  cornea;   the 
anterior  portion  again  increases  in  thickness. 

Cornea. — It  is  joined  to  the  sclerotic  coat  by  direct  continuity 
of  tissue.  The  tissue  of  the  cornea  absorbs  water  readily  and  becomes 
opaque  after  death.  The  cornea  has  five  layers.  The  first,  or  anterior, 
epithelial  layer  is  composed  of  several  layers  of  epithelial  cells;  the 
deepest  are  cylindrical,  which  pass  over  into  the  lower  polygonal 
cells,  which,  on  the  surface,  become  flat,  nucleated  cells.  At  the  edge 
of  the  cornea  this  epithelium  becomes  continuous  with  that  of  the 
conjunctiva.     Second  layer:  the  anterior  elastic  lamina  (of  Bowman) 


Vig.  322. — Anterior-postei-ior  Section  of  the  Eyeball.     (Leveill:^.) 

1,  Optic  nerve.  2,  Sclerotic.  3,  Cornea.  4,  Spaces  of  Fontana.  5,  Choroid. 
6,  Ciliary  muscle.  7,  Ciliary  processes.  8,  Iris.  9,  Retina.  10,  Jacobs's  mem- 
brane. 11,  Anterior  chamber.  12,  Posterior  chamber.  13,  Pupillary  area.  14, 
Aqueous  humor.  15,  Hyaloid  membrane.  16,  Canal  of  Stilling.  17,  Canal  of 
Petit.  18,  Vitreous  humor.  19,  Capsule  of  the  lens.  20,  Fluid  of  Morgagni. 
21,  Lens. 


is  formed  by  the  superficial  part  of  the  proper  structure  of  the  cornea, 
which  is  denser  than  the  rest  of  the  tissues  and  free  from  cor- 
puscles. This  layer  is  strongly  developed  in  man  and  is  a  homogene- 
ous refractive  membrane.  Fibrils  can  be  demonstrated  in  it  by 
means  of  certain  reagents.  Third  layer:  the  substantia  propria,  or 
the  cornea  proper,  forms  the  main  mass  of  the  cornea.  It  consists 
of  fibrils  of  connective  tissue  bound  together  in  flat  lamella  (about 
60  in  number).  The  fibrils  run  in  various  directions,  and  cross  each 
other  at  various  angles.  Between  the  lamelhe  are  canals  and  spaces 
which  contain  a  serous  fluid.  In  these  spaces  are  found  the  connec- 
tive-tissue cells,  having  many  processes  and  large  nuclei,  around 
which  the  serous  fluid  trickles  to  carry  nutriment  to  the  surround- 


702 


PHYSIOLOGY. 


ing  tissue.  By  the  chloride  of  gold  method  a  picture  is  obtained  of 
this  system  of  canals.  The  fourth  layer:  the  posterior  elastic  layer, 
or  membrane  of  Descemet.     This  lamina  is  about  V2500  of  an  inch 


Fig.  323. — Section  through  the  Human  Cornea.     (BoHM  and  Davidoff.  ) 

1,    Anterior   epithelium.     2,    Basal   colls.     3,    Bowman's   layer. 
4,  Substantia  propria. 

thick,  firm,  refractive,  and  homogeneous  in  structure.  When  pieces 
of  this  layer  are  separated,  they  curl  up  with  the  attached  surface 
innermost.     At  its  circumference  the  lamina  breaks  up  into  bundles 


Fig  324. — Corneal   Corpuscles  of  Dog.      (BoHM  and  Davidoff.) 


of  fibers,  some  of  which  form  the  pillars  of  the  iris.  To  these 
radiating  and  anastomosing  bundles  of  elastic  fibers  prolonged  from 
the  circumference  of  Descemet's  membrane  has  been  sriven  the  name 


VISION.  703 

of  pectinate  ligament.  The  fifth  layer  of  the  cornea  is  the  posterior 
epithelial  layer,  composed  of  low,  hexagonal  cells.  The  epithelium 
is  deficient  at  the  circmnference  in  the  interval  between  the  pillars 
of  the  iris.  The  openings  formed  are  mouths  of  cavernous  spaces 
(the  spaces  of  Fontana),  which  lead  into  the  circumferential  channel 
(canal  of  Schlemm),  through  the  intervention  of  which  the  aqueous 
chamber  is  placed  in  connection  with  the  canal  of  Schlemm,  which 
is  a  lymphatic  channel.  The  cornea  contains  no  blood-vessels.  The 
corneal  nerves  enter  into  the  substantia  propria  of  the  cornea,  where 


Fig.   325. — Corneal   Nerves   of   the   Pig.      (Rollet.) 

1,  1,  Larger  nerves.     2,   Plexus  beneath   Bowman's  layer.     3,  3,  Terminal  twigs 
ascending  through  the  epithelium.     4,   Sub-epithelial  plexus. 

they  lose  their  medullary  sheaths  and  form  four  plexuses  at  different 
levels : — 

1.  The  ground  plexus,  in  the  deep  layer  of  the  substantia 
propria. 

2.  The  subbasal  plexus. 

3.  The  subepithelial  plexus. 

4.  The  intraepithelial  plexus,  which  consists  of  fine  fibers  run- 
ning between  the  epithelial  cells,  ending  in  knoblike  terminations. 

Choroid. — The  dark-brown  choroid  coat  is  the  vascular  coat 
of  the  eye.  It  consists  of  two  parts,  which  are  continuous  with  one 
another — the  choroid  and  the  iris.  The  choroid  is  composed  of  sev- 
eral layers.  Externally  it  is  bounded  by  a  nonvascular  membrane, 
the  lamina  supra  choroidca.     The  arteries  groove  the  sclerotic  coat 


704 


PHYSIOLOGY. 


before  passing  into  the  choroid.  After  entering  its  substance  they 
go  beneath  the  veins,  while  the  latter  (vasa  vorticosa)  receive  their 
tributaries  as  curved  branches  arranged  in  a  peculiar  form,  which 


Fig.  326. — Diagram  of  the  Vessels  of  the  Eye.      (Leber.) 

1,  Cornea.  2,  Sclera.  3,  Lens.  4,  4,  Short  ciliary  nerves.  5,  Long  posterior 
ciliary  artery.  6,  Anterior  ciliary  artery  and  vein.  7,  Posterior  conjunctival 
artery  and  vein.  9,  Vessels  of  the  internal  optic  sheath.  8,  Vessels  of  the 
external  optic  sheath.  11,  Vena  vorticosa.  12,  Posterior  short  ciliary  vein.  13, 
Branch  of  short  posterior  ciliary  artery  to  the  optic  nerve.  14,  Anastomosis  of 
choroidal  vessels  with  those  of  the  optic  nerve.  15,  Chorio-capillaris.  16, 
Episcleral  branches.  17,  Recurrent  choroidal  artery.  18,  Large  arterial  circle  of 
Iris  (transverse  section).  19,  Vessels  of  iris.  20,  Ciliary  prccess.  21,  Branch 
of  vena  vorticosa  from  the  ciliary  muscle.  22,  Branch  of  anterior  ciliary  vein 
from  the  ciliary  muscle.  23,  Canal  of  Schlemm.  24,  Plexus  of  the  corneal 
margin.    25,  Anterior  conjunctival  artery  and  vein. 

has  been  compared  to  the  branching  of  a  weeping  willow,  and  form 
four  or  five  large  trunks,  which  pierce  the  sclerotic  half  way  between 
the  optic  nerve  entrance  and  the  edge  of  the  cornea.     In  the  inter- 


VISION. 


705 


vals  between  the  vessels  are  elongated,  stellate  pigment-cells.  The 
inner  part  of  the  choroid  is  formed  mainly  by  capillary  blood-vessels 
(tunica  Euyschiana  vel  chorio-capillaris).  This  reaches  to  one- 
eighth  of  an  inch  from  the  corneal  margin,  where  its  vessels  join 
those  of  the  ciliary  processes.  On  the  inner  surface  of  the  tunica 
Euyschiana  is  a  structureless  membrane,  the  membrane  of  Bruch, 
which  lies  next  to  the  pigmentary  layer  of  the  retina.     The  choroid 


Fig.  .327. — Meridional  Section  of  the  Human  Ciliary  Body. 
(BoHM  and  Davidoff.  ) 

1,  2,  Conjunctiva.  3,  Sclera.  4,  Meridional  fibers  of  tlie  ciliary  muscle. 
5,  Ciliary  processes.  6,  Circular  fibers  of  the  ciliary  muscle.  7,  Iris  pigment. 
8,  Stroma  of  iris.  9,  Canal  of  Schlemm.  10,  Membrane  of  Descemet.  11,  Cor- 
nea.    12,  Corneal  epithelium. 

coat  ends  anteriorly  in  the  ciliary  processes  and  the  iris.  The 
ciliary  processes  consist  of  about  seventy  to  eighty  ridgelike  pro- 
cesses running  meridionally.  They  are  arranged  around  the  lens, 
and  toward  the  outside  the  ground-substance  of  the  processes  bor- 
ders on  the  ciliary  muscle.  They  have  the  same  structure  as  the 
choroid,  and  contain  very  numerous  blood-vessels,  derived  from  the 
anterior  ciliary  arteries. 

45 


706  PHYSIOLOGY. 

Uses. — By  reason  of  its  vascularity  the  choroid  is  destined  to 
nourish  the  all-important  and  underlying  retina.  By  reason  of  its 
elasticity  and  contained  musculature  the  choroid  maintains  intra- 
ocular pressure.  The  pigment  of  the  choroid  is  believed  to  serve  a 
dioptric  purpose:  that  of  absorbing  the  superfluous  rays  of  light 
which  pass  through  the  eyeball  on  their  way  to  the  retina.  Their 
absorption  prevents  dazzling  and  interference  with  vision. 


Fig.   328. — Dissection   of   the   Zonula.      (After   Schultze. ) 
1,  Lens.    2,  Cut  surface  of  iris,     3,  Ciliary  processes.     4,  Choroid.     5,  Zonula. 

Ciliary  Muscle. — The  libers  of  this  muscle  can  be  divided  into 
three  parts:  (1)  The  strongest  layer  is  nearest  the  sclerotic.  It  is 
composed  of  a  thick  layer  of  fibers  having  a  meridional  direction, 
which  extend  backwards  into  the  choroid.  (3)  The  second  part  of 
the  muscle  contains  fibers  which  are  less  intimately  connected  with 
each  other.  Their  direction  deviates  more,  and  they  radiate  towards 
the  center  of  the  ocular  globe.  These  fibers  terminate  near  the  pos- 
terior surface  of  the  ciliary  body.  (3)  The  third  part  of  the  ciliary 
muscle  is  represented  by  the  ring-muscle  of  H.  Miiller,  and  is  much 


VISION. 


707 


developed  in  hypermetropic  eyes,  and  atrophied  or  absent  in  myopic 
eyes.  It  is  composed  of  circular  fibers,  which  form  a  ring  parallel 
with  the  base  of  the  cornea.  The  ciliary  muscle  arises  from  the 
sclerotic  close  to  the  cornea;  its  fibers  are  inserted  into  the  pecti- 
nate ligament,  and  extend  to  be  attached  to  the  choroid,  as  has  Just 
been  described. 

Ciliary    Buthj. — This    includes    the    ciliary    processes    and    the 
ciliary  muscle. 


Fig.  329. — Lateral  View  of  the  Orbit,  Showing  the  Nerves.     (Deaver.) 

1,  Antrum.  2,  Bristle  in  the  antrum.  3,  Loop  between  orbital  and  lacrimal 
nerves.  4,  Tarsal  plate.  5,  Lacrimal  gland.  6,  Tendon  of  superior  oblique.  7, 
Pulley  of  the  same.  8,  Infundibulum.  9,  Frontal  sinus.  10,  Supra-orbital  nerve. 
11,  Supra-trochlear  nerve.  12,  Levator  palpebrge  muscle.  O,  Lacrymal  nerve. 
J,  Superior  rectus  muscle.  A,  Frontal  nerve.  13,  Internal  rectus  muscle.  14, 
Optic  nerve.  15,  Short  ciliary  nerve.  16,  Nasal  nerve.  17,  Ciliary  ganglion.  18, 
Lacrimal  nerve.  19,  Motor  oculi  nerve.  20,  Patheticus  nerve.  21,  Abducens 
nerve.  22,  Ophthalmic  division  of  the  fifth  nerve.  23,  Gasserian  ganglion.  24. 
Fifth  nerve.  25,  Inferior  maxillary  nerve.  26,  Superior  maxillary  nerve.  27, 
Orbital  nerve. 


Iris.- — This  body  is  to  be  considered  as  a  process  of  the  choroid. 
It  is  made  up  of  four  layers:  (1)  The  anterior  epithelium,  made  of 
flat  cells,  which  cover  the  anterior  surface  of  the  iris.  (2)  The 
stroma  of  the  iris,  which  consists  of  connective  tissue  which  contains 
numerous  blood-vessels,  which  are  radially  arranged  and  have  no 
muscular  sheaths.  In  this  part  of  the  iris  the  smooth  muscle-cells 
are  collected  to  form  the  sphincter  and  dilator  muscles  of  the  pupil. 
The  sphincter  muscles  are  arranged  circularly  around  the  edge  of 
the   pupil.     The   dilating  muscles   run   in   a   radial   manner.     The 


708 


PHYSIOLOGY. 


coloring  inn  tier  which  is  found  in  the  connective  tissue  of  the 
stroma  of  (he  ii'is,  and  its  varying  (juantity,  give  the  color  to  the 
iris.  (3)  The  posterior  limiting  layer,  or  a  portion  of  Bruch's  mem- 
brane. (-1)  The  pigment  layer  (uvea).  This  is  made  up  of  two 
layers  of  cells;  the  posterior  layer  is  cubical  and  full  ol'  j)igment, 
the  anterior  layer  is  Hat  and  contains  only  a  small  amount  of  pig- 
ment. This  pigment-layer  is  a  continuation  anteriorly  of  the  pig- 
ment-layer of  the  retina.  The  color  of  the  iris  is  due  to  pigmented 
connective-tissue  corpuscles,  especially  in  brunettes.  The  artery 
and  veins  of  the  iris  lie  at  its  periphery. 


OPTIC      CENTIie.- /— ~ 


Fig.  330. — The  Nervous  Meclianism  of  the  Iris. 


The  pupil  is  made  smaller  by  contraction  of  its  circular  fibers. 
These  belong  to  the  smooth  type  of  muscle-fibers  and  are  innervated 
by  the  oculomotor  through  the  medium  of  its  ciliary  branches. 

The  pupil  enlarges  through  contraction  of  the  radiating  fibers 
of  the  iris.  It  is  innervated  by  the  ciliary  branches  derived  from 
the  great  sympathetic.  Sensory  nerves  are  present,  coming  from 
the  first  branch  of  the  fifth,  or  trigeminus. 

Hence,  stimulation  of  the  oculomotor  and  trigeminus,  as  well 
as  cutting  the  sympathetic  nerve  in  the  neck,  produces  contraction 
of  the  pupil.  Irritation  of  the  sympathetic  causes  the  pupil  to 
dilate.  The  normal  contraction  and  dilatation  of  the  pupil  are  re/?e;c 
movements  that  are  caused  by  the  rays  of  a  very  strong  or  very  faint 
light  striking  the  retina.     From  the  retina  the  impression  is  con- 


VISION. 


709 


veyed  by  the  optic  nerve  to  the  anterior  corpora  (juadrigemina  and 
then  to  tlie  oculomotor  nucleus  and  by  its  nerves  to  the  iris.  It  is  not 
due  to  the  direct  action  of  liglit  upon  the  iris  itself. 

The  following  cause  changes  in  the  diameter  of  the  pupil: — 
Contraction  of  Pupil. — Stimulation  of  optic  nerve;  stimulation 
of  third  cranial  nerve ;  section  of  fifth  cranial  nerve ;  section  or 
paralysis  of  the  cervical  sympathetic;  light  acting  on  retina;  accom- 
modation for  a  near  object;  myotics  (eserin,  stimulation  of  the  ends 
of  oculomotor) ;  ana?sthetics  (at  first). 

Dilatation-  of  Pupil.- — Section  of  the  optic  nerve;    paralysis  of 
third  cranial  nerve;   stimulation  of  fifth  cranial  nerve;   stimulation 


Fig.    331. — Isolated    Lens    Fibers.       (J.    Arxold.) 

of  sympathetic;  stimulation  of  sensory  nerves;  mydriatics  (atropin, 
by  paralyzing  the  ends  of  oculomotor);  dyspnoea,  asphyxia;  anaes- 
thetics (at  the  end). 

Meltzer  and  Auer  have  shown  that,  with  the  superior  cervical 
ganglion  present,  adrenalin  does  not  act  on  the  pupil.  When  the 
ganglion  is  removed,  then  adrenalin  dilates  the  pupil.  I  have  con- 
firmed this  statement. 

The  Ceystallixe  Lexs. — The  lens  is  situated  behind  the  iris, 
and  enclosed  in  a  distinct  capsule.  The  lens  consists,  in  the  begin- 
ning, of  cylindrical  cells,  which  in  the  course  of  development  in- 
crease in  height,  until  exceedingly  long  cells  are  formed.  The  lens- 
fibers  are  flattened  hexagonal  prisms,  which  are  thickened  at  their 
posterior  ends.     They  run  in  a  meridional  direction  from  the  an- 


710  PHYSIOLOGY. 

terior  surface  backward,  joined  by  a  small  quantity  of  cement  sub- 
stance. The  outer  fibers  have  oval  nuclei,  whilst  in  the  center  of 
tlie  lens  no  nuclei  are  found.  The  capsule  of  the  lens  is  thicker  on 
the  anterior  surface  tbi'.n  on  the  posterior.  It  is  a  clear,  refractive 
membrane,  nonvascular.     Between  the  anterior  surface  of  the  lens 


Fig.   332. — Transverse  Section  of  Lens   Fibers.      (J.   Arxold.) 

and  the  capsule  there  is  a  single  layer  of  cubical,  nucleated  cells. 
The  radius  of  curvature  of  the  anterior  surface  of  the  lens  varies 
with  the  accommodation  for  distant  vision.  It  is  about  10  milli- 
meters to  0  millimeters  in  near  point  of  distinct  vision. 

Cataract. — Normally  the  lens  is  transparent.  When  it  becomes 
opaque  for  any  reason,  then  there  results  the  condition  known  as 
cataract.  Tliis  condition  is  artificially  produced  in  frogs  by  the 
injection  of  grape-sugar.  Cataract  in  diabetes  is  from  the  same 
cause. 


Fig.  333. — Anterior  Surface  of  tlie  l^cns  of  an  Adult.     (J.  Arnold.) 

The  Eetina. — The  retina  contains  the  terminations  of  the 
optic-nerve  fibers.  It  ends  at  the  pupillary  border  of  the  iris.  The 
optical  part  of  the  retina  ends  in  the  ora  serrata,  a  zigzag  line  in  the 
vicinity  of  the  ciliary  body. 

Bods  and  Cones. — Each  rod  consists  of  a  rod  and  a  rod-fiber, 
the    fiber   containing   the    nucleus.     The    rods    are    cylindrical   and 


VISION. 


711 


elongated.  The}'  are  divided  into  two  parts,  the  outer  segment  and 
the  inner.  Tlie  outer  segment  is  doubly  refracting,  contains  the 
visual  purple,  and  breaks  up  into  many  superposed  discs  when  acted 


Fig.   3.34. — Diagram  of  the  Structure  of  the  Human  Retina  According 
to  r4olgi's  Method.     (Greeff.) 

I,  Pigment  epithelium  layer.  II,  Rods  and  cones.  Ill,  Granules  of  the  visual 
cells.  IV,  Outer  plexiform  layer.  V,  Layer  of  horizontal  cells.  VI,  Layer  of 
bipolar  cells.  VII,  Layer  of  amakrine  cells.  VIII,  Inner  plexiform  layer.  IX. 
Ganglion  cell  layer.  X,  Layer  of  nerve  fiber.  1,  Diffuse  amakrine  cell.  2, 
Diffuse  ganglion  cell.  3,  Centrifugal  nerve  fiber.  4,  Amakrine  association  fiber. 
5,   Neuroglia  cells.     6,   Miiller's  radial  fibers. 

upon  by  certain  reagents.  The  inner  segment  is  spindle-shaped, 
granular,  and  singly  refractive.  The  ellipsoid  of  Kraus  is  in  the 
outer  part  of  the  inner  segment,  and  exhibits  a  fibrous  structure. 


712 


PHYSIOLOGY. 


The  rod-fiber  is  a  contiiination  at  its  inner  end  of  the  rod.     The 
fiber  contains  the  rod-nnclous. 

Cones. — Both  rods  and  cones  are  closely  set  lilvc  a  palisade  over 
the  whole  extent  of  the  retina,  between  the  external  limiting  mem- 
brane and  the  pigmentary  layer,  except  at  the  macula  lutea,  where 
there  are  only  cones.  The  smallest  angular  distance  at  which  points 
can  be  separately  distinguished  is  50  seconds,  with  which  the  size 
of  a  retinal  image  is  3.G5  micromillimeters.  This  size  coincides 
closely  with  the  diameter  of  the  cones  at  the  fovea,  which  are  about 
3  micromillimeters. 


Fig.  335. — Hexagonal  Cells  from  the  Pigment  Layer  of  the  Retina  of  a 
Rabbit.      (Ball.) 

The  cones,  like  the  rods,  consist  of  two  segments,  an  inner  and 
an  outer.  The  cones  are  shorter  than  the  rods.  The  outer  seg- 
ment of  the  cone  has  cross  striations.  The  inner  segment  is  much 
thicker  and  shorter  than  the  rod,  and  is  rounded.  The  ellipsoid  of 
the  cone  is  larger  than  that  of  the  rod,  and  lies  in  the  peripheral 
part  of  the  inner  segment.  A  cone-fiber  is  a  continuation  of  the 
cone.  Between  each  cone  there  are  usually  two  or  three  rods,  show- 
ing the  greater  abundance  of  rods.  The  external  limiting  mem- 
brane is  a  product  of  the  Miiller  fibers,  the  sustentacular  tissue  of 
the  retina.     In  the  vicinity  of  the  ora  serrata  the  nerve-fiber  and 


VISION. 


713 


ganglion-cell  first  disappear.  At  a  certain  distance  from  the  ora 
serrata  the  rods  disappear,  and  then  the  cone-cells  change  and 
become  a  layer  of  cylindrical  epithelium. 

Tlie  Pigmentary  Layer. — It  is  composed  of  hexagonal  pigment- 
cells.  The  outer  surface  of  the  cell,  turned  towards  the  choroid,  is 
smooth  and  flattened,  and  the  part  of  the  cell  near  this  surface  is 
without  pigment  and  is  nucleated.  The  inner  boundary  of  the  cell 
is  loaded  with  pigment  and  is  prolonged  into  fine,  straight,  filament- 
ous processes,  which  reach  for  a  certain  distance  into  the  outer  seg- 


A  B 

Fig.  336. — Action  of  the  liight  on  Retina.  Section  of  retina  of  frog. 
(Englemann.)  (From  Tigerstedt's  "Human  Physiology-."'  copyright, 
1006,  by  D.  Appleton  and  Company.) 

A,    After    two    days    of   rest,    animal    in    dark,    pigment    concentrated,    cones 
protruded.     B,  After  diffuse  daylight,  cones  retracted,  pigment  diffused. 

ments  of  the  rods  and  cones,  which  are  imbedded  in  the  pigment- 
cells.  The  pigment  is  in  the  form  of  small,  dark-brown  granules  and 
rods.  In  the  dark,  the  pigment  is  mainly  heaped  up  in  the  body 
of  the  cell;  but  when  light  strikes  the  pigment,  it  is  drawn  in 
between  the  rods.  The  pigment  seems  to  renew  the  visual  purple  of 
the  outer  segment  of  the  rods  after  they  have  been  bleached  by  the 
light.     The  eyes  of  albinos  have  no  pigment  in  the  cells. 

Macula  Lvtea. — The  yellow  spot  of  Soemmering  is  an  oval  de- 
pression in  the  center  of  the  retina.     It  measures  one-twentieth  of 


714 


PHYSIOLOGY. 


an  inch  across  and  is  one-tenth  of  an  inch  to  the  outer  side  of  the 
])oint  of  entrance  of  tlie  o])ti(;  nerve.  Jts  center  is  the  fovea  cen- 
iralis.  In  I  lie  fovea  there  are  no  rods:  cones  only  ai'e  |)resent,  and 
these  are  longer  and  narrower  than  those  of  the  other  i)arts  of  the 
retina. 

When  tlie  optic  nerve  penetrates  the  eye  it  projects  somewhat 
beyond  the  inner  surface  of  the  eyeball  as  a  papilla.  In  this  papilla 
there  are  none  of  the  essential  nerve-elements  of  the  retina,  so  that 
rays  of  lif^iit  cannot  be  perceived  l)y  this  particular  area;  hence  the 
name  of  blind  spot. 

The  nervous  layer  of  the  retina  is  composed  princi])ally  of  the 
terminal  nerve-elements  of  the  optic  nerve.     Externally,  it  is  coated 


Fig.   .337.— Riglit   Eye,  Normal   Fundus   Oculi.      (Ball.) 


with  a  pigment-layer;    internally,  it  is  lined  with  a  homogeneous, 
transparent  structure,  the  hyaloid  membrane. 

Histological  Structure. — The  histological  structure  of  the  retina 
is  very  complicated.  The  retina  is  really  an  outward  expansion  of 
the  original  forebrain.  The  retina  is  usually  divided  into  eight 
layers : — 

1.  The  layer  of  nerve-fibers. 

2.  The  layer  of  ganglionic  cells. 

3.  The  inner  molecular  layer. 

4.  The  inner  nuclear  layer. 

o.  The  outer  molecular  layer. 
(').  The  outer  nuclear  layer. 

7.  The  layer  of  rods  and  cones. 

8.  The  hexagonal  pigment-layer. 


VISION. 


715 


The  first  layer  consists  of  neiiraxons  from  tho  ganglionic  cells 
of  the  second  layer.  The  second  layer  consists  of  a  lot  of  mnlti- 
polar  nerve-cells,  and  their  neuraxons  run  inward  to  form  most  of 
the  fibers  of  the  optic  nerve.  The  dendrons  of  these  multipolar 
cells  are  branched  and  terminate  in  the  inner  molecular  layer,  of 
which  this  third  layer  is  chiefly  composed.  The  fourth  inner  nuclear 
layer  is  made  up  chiefly  of  round  and  oval  cells  with  a  peripheral 
neuraxon  and  a  central  neuraxon. 

The  peripheral  neuraxon  arborizes  around  the  dendrons  of  a 
ganglionic  cell  in  the  inner  molecular  layer. 

The  fifth  outer  molecular  layer  is  made  up  of  the  arborizations 
of  the  neuraxons  of  the  visual  cells  of  the  outer  nuclear  layer. 


lobuL 


f.  of  Rolando 
intraparietal  fissure 

/.  of  Sylirius 
parallel  fissure 


corpus 


fascia.  . 
denlata 


A  B 

Fig.  338.— Diagram  of  Occipital  Region  of  Riglit  Cerebral  lleiuisplieres. 

(Ball.) 
A,   From  iniior,  and  li,   from  outer  aspect. 

The  sixth  layer,  the  outer  nuclear  layer,  is  the  layer  of  bipolar 
visual  cells.  Their  central  neuraxons  end  in  arborizations  in  the 
outer  molecular  layer  about  the  dendrons  of  the  bipolar  cells  of  the 
inner  nuclear  layer.  The  peripheral  processes  of  these  cells  are  the 
rods  and  cones  of  the  retina,  which  are  similar  to  the  dendrons  of 
other  nerve-cells. 

The  seventh  layer  of  rods  and  cones  are  the  dendrons  of  the 
visual  cells. 

The  eighth  layer  is  the  pigment-layer  of  the  retina. 

The  retina  is  essentially  formed  by  a  number  of  nerve-cell 
chains,  the  elements  of  which  are  arranged  in  three  series  from  with- 
out in.  The  first  is  the  rod  and  tlie  cone;  the  second  is  the  bipolar 
cell,  which  interlaces  with  the  peripheral  dendrons  of  the  ganglonic 
cells.     The  third  element  is  the  ganglion-cell. 


716  PHYSIOLOGY. 

Tlic  optic  tract  arises  in  the  retinal  cells,  which  are  its  trophic 
center.  These  retinal  cells  send  in  fibers  which  arborize  around  the 
cells  of  the  anterior  corpora  quadrigemina,  pulvinar,  and  the  lateral 
corpus  geniculatum.  ^Now,  from  the  lateral  corpus  geniculatum  and 
pulvinar  we  have  a  second  set  of  neuraxons  running  to  the  occipital 
cortex,  the  center  of  vision.  Here  the  lateral  corpus  geniculatum 
and  pulvinar  are  the  relay  centers  in  the  path  of  visual  impulses. 

The  Vitreous  Humor. — The  hyaloid  membrane,  a  homogene- 
ous capsule,  encloses  the  vitreous  humor.  This  hyaloid  membrane 
divides  as  it  cdmes  forward  over  the  vitreous,  one  part  going  to  the 
capsule  of  the  lens  as  the  zonule  of  Zinn,  and  the  other  passing  in 
front  of  the  vitreous.  The  free  part  of  the  hyaloid,  stretching  from 
the  capsule  of  the  lens  to  the  ciliary  body,  is  termed  the  suspensory 
ligament  of  the  lens.  Between  these  two  layers  of  the  hyaloid  the 
canal  of  Petit  is  formed,  a  lymphatic  canal.  In  the  center  of  the 
vitreous  is  the  canal  of  Stilling,  which,  in  the  foetal  state,  was  the 
pathway  of  the  artery  of  Zinn  to  the  posterior  part  of  the  capsule 
of  the  lens.  The  vitreous  has  no  blood-vessels,  and  is  composed 
chemically  of  water,  98.5  per  cent.,  and  salts,  extractives,  and  traces 
of  proteid  and  nucleo-albumin.  The  vitreous  has  fine  intercrossing 
connective-tissue  fibers,  connective-tissue  cells,  and  leucocytes. 

Aqueous  Humor. — This  fluid  contains  about  2  per  cent,  of 
solids,  chiefly  in  the  form  of  sodium  chloride.  It  occupies  the 
anterior  chamber  in  the  space  back  of  the  cornea  and  in  front  of 
the  iris.  The  so-called  posterior  chamber  lies  between  the  back  of 
the  iris  and  in  front  of  the  lens. 

When  by  ulceration  of  the  cornea  or  accident  the  aqueous  humor 
escapes,  it  is  found  to  be  regenerated  very  rapidly. 

The  secretion  of  the  aqueous  humor  has  been  studied  by  fluore- 
scin  instilled  into  the  fluids  of  the  eyeball.  It  has  been  found  that 
ihe  humor  is  secreted  by  the  posterior  surface  of  the  iris  and  ciliary 
body.     It  passes  through  the  pupil  into  the  anterior  chamber. 

Blood-vessels  of  the  Eye. — There  are  two  systems  of  blood- 
vessels: the  retinal  and  the  ciliary  system.  These  systems  are 
separate,  and  anastomose  only  at  the  j^lace  of  entrance.  The  retinal 
system  is  the  central  artery  of  the  retina,  which  goes  through  the 
axis  of  the  optic  nerve  until  it  reaches  the  optic  papilla,  where  it 
divides  into  two  branches,  one  running  forward  and  the  other  in  a 
posterior  direction.  These  vessels  are  seen  with  the  ophthalmo- 
scope. 


VISION. 


717 


Tha  Cilianj  System. — These  break  through  the  sclera  to  supply 
the  choroid,  the  ciliary  body,  and  the  iris. 

The  short  ciliary,  about  six  to  twelve  in  number,  supply  the 
choroid  and  ciliary  processes. 

The  long  ciliary,  two  in  number,  penetrate  the  sclerotic,  run 
forward  between  the  choroid  and  sclerotic  to  the  ciliary  muscle, 
forming  a  very  vascular  circle  about  the  iris. 


Fie 


339. — Diagram  of  the  Lymph  Spaces  of  the  Eyeball. 
(After  FucHS.) 


1,  Anterior  chamber.  2,  Posterior  chamber.  3,  Canal  of  Sohlemm.  4,  Hya- 
loid canal.  5,  Anterior  ciliary  vein.  6,  Continuation  of  Tenon's  capsule  on  the 
ocular  tendons.  7,  Lymph  space  around  the  vena  vorticosa.  8,  Perichoroidal 
space.     9,   Supra-vaginal  space.     10,   Inter-vaginal  space.' 

In  deep-seated  ciliary  congestion  you  have  a  pus-zone  about  the 
cornea,  which  is  much  different  from  the  bloodshot  eye  of  conjunc- 
tivitis. 

The  capsule  of  Tenon  is  a  thin  membrane  which  envelops  the 
eyeball  from  the  optic  nerve  to  the  ciliary  region,  forming  a  socket 
in  which  it  plays.  On  its  inner  surface  it  is  smooth,  and  is  in  con- 
tact with  the  outer  surface  of  tlie  sclerotic,  tlie  perisclerotic  lymph- 


718 


PIIYRTOLOGY. 


space  lying  between  it  and  the  sclerotic.  There  are  some  nnstriped 
muscular  fibers  in  the  capsule  of  Tenon.  These  muscular  libers  are 
innervated  by  the  cervical  sympathetic,  and  project  the  eyeball  when 
in  action. 

Intraocular  rrcssurc. — The  iiiiraocular  pressure  depends  upon 
the  tension  of  blood  in  the  arteries  of  the  eye.  The  pressure  under- 
goes oscillations  simultaneous  with  the  pulse  and  respiratory  move- 
ments. 

The  pressure  is  about  20  to  30  millimeters  of  mercury. 


Fig.   .'MO. — .Schematic  Eye   three   Times  Natural    Size.      (Landolt.) 

(j)'.  Anterior  or  principal  focus.  A,  Anterior  surface  of  cornea.  //'  and  H", 
Principal  points.  K'  and  A"',  Nodal  points.  0",  Posterior  or  second  principal 
focus.    F.c,  Fovea  centralis.    <^',   (p",  Optic  axis. 


The  aqueous  humor,  which  is  secreted  and  absorbed  with  great 
ease,  appears  to  regulate  the  pressure. 

Lymphatics.— The  lymphatics  of  the  eye  comprise  an  anterior 
and  posterior  set.  The  former  is  located  in  the  anterior  and  posterior 
chambers  of  the  eye  and  has  communication  with  the  lymphatics  of 
the  iris,  ciliary  processes,  cornea,  and  conjunctiva.  The  posterior 
set  consists  of  the  perichoroidal  spaces  lying  between  the  choroid 
and  sclerotic  coats  of  the  eyeball. 


VISION.  719 

Optic  Nerve. 

The  optic  ner\'e  contains  centripetal  and  centrifugal  tibers. 
The  bundle  of  centripetal  tibers  from  the  second  layer  of  retinal 
ganglionic  cells,  which  originate  in  the  vicinity  of  the  macula,  go 
into  the  optic  tract  of  the  same  and  opposite  side.  Those  going  into 
the  optic  tract  of  the  same  side  come  from  the  temporal  tract  of 
the  macuhi,  while  the  decussating  fibers  come  from  the  nasal  side 
of  the  macula ;  hence  each  optic  tract  is  made  up  of  fibers  from  the 
temporal  half  of  the  retina  of  the  same  eye  and  from  the  nasal  half 
of  the  opposite  eye.  The  optic  tract  then  goes  backward,  passing 
around  the  cerebral  peduncle,  and  breaks  up  into  two  bundles,  the 
external  and  the  internal.  The  internal  bundle  is  connected  with 
the  internal  geniculate  body  and  the  posterior  corpus  quadrigeminum, 
and  is  a  part  of  Gudden's  commissure.  It  has  no  connection  with 
vision.  The  external  bundle  goes  to  the  external  geniculate  body, 
the  i^ulvinar  and  anterior  corpus  quadrigeminum.  The  cells  in  the 
external  geniculate  body  receive  the  terminal  arborizations,  as  also 
do  the  cells  of  the  pulvinar  and  corpus  quadrigeminum.  From  these 
ganglia  neuraxons  go  through  the  most  posterior  end  of  the  internal 
capsule  (optic  radiations  of  Gratiolet),  to  end  in  the  occipital  lobe, 
mainly  in  the  cuneus. 

The  pyramidal  cells  send  centrifugal  fibers  to  the  external  geni- 
culate body,  to  the  pulvinar  and  the  anterior  corpus  quadrigeminum, 
and  from  here  new  centrifugal  axons  go  to  the  retina. 

Irritation  of  the  occipital  cortex  in  the  monkey,  say  of  the  right 
lobe,  causes  movement  of  the  eyes  to  the  opposite  side,  through  the 
action  of  the  efferent  fibers. 

The  average  dimensions  of  the  dioptric  system  of  the  eye  are 
as  follows: — 

Index  of  refraction  of  air 1. 

Index  of  refraction  of  cornea,  aqueous  luinior,  and  vitreous 

bod}' 1.3365 

Total  index  of  refraction  of  the  crystalline  lens 1.4371 

Radius  of  curvature  of  the  cornea 7.829  mm. 

Radius  of  curvature  of  the  anterior  surface  of  the  crystal- 
line lens   10.0      mm. 

Radius  of  curvature  ol  the  posterior  surface  of  the  crystal- 
line lens   (5.0      mm. 

Distance  from  the  apex  of  the  cornea  to  tlie  anterior  sur- 
face of  the  crystalline  lens 3.G      mm. 

Distance  from  the  apex  of  the  cornea  to  the  posterior  sur- 
face of  the  crystalline  lens 7.2      mm. 

Thickness  of  the  lens 3.6      mm. 


720  PHYSIOLOGY. 

Using  the  above  values,  the  positions  of  the  cardinal  points  of 
Gauss,  of  the  human  eye  on  the  optical  axis,  calculated  from  the 
apex  of  the  cornea,  are  as  follows: — 

Tlie  first  principal  focus  is  situated  13.745  millimeters  in  front 
of  the  cornea. 

The  other  points  ai'c  behind  the  cornea: — 

The  first  principal  [joint 1.75:32  mm. 

The  second  principal  point 2.1101  mm. 

The  difference  is 0.35U9  mm. 

The  first  nodal  point '. G.9085  mm. 

The  second  nodal  point 7.;3254  mm. 

The   second   principal    focus 2.282;}7  mm. 

These  values  are  shown  in  Fig.  340,  but  are  three  times  as  great 
as  in  nature. 

From  these  data  are  shown  the  course  of  rays  through  the  eye 
and  the  position  and  size  of  images. 

Perception  of  Light. 

Light  is  due  to  vibrations  of  ether;  a  proper  conception  of  them 
gives  the  sensation  of  sight.  Transmission  of  light,  with  air  as  a 
medium,  is  186,0U0  miles  per  second.  The  rapidity  of  the  vibra- 
tions influences  the  sensation  produced,  for  color  is  for  luminous 
sensation  what  height  is  for  sound.  The  inferior  limit  of  visible 
vibrations  is  represented  by  the  color  red;  the  superior  limit  is 
exemplified  in  violet. 

For  light  to  be  perceived  physiologically  by  any  individual  it 
must  make  an  impression  ui^on  the  retina.  The  light  falling  upon 
the  retina  immediately  stirs  uj)  certain  changes  in  it  which  in  turn 
give  rise  to  nervous  changes  in  the  fibers  of  the  optic  nerve.  This 
last  change,  or  "visual  impulse,"  produces  a  further  series  of  events 
within  the  brain,  one  effect  of  which  is  a  change  in  our  conscious- 
ness;   that  is,  there  is  a  sensation. 

The  point  upon  the  retina  at  which  the  impressions  are  strongest 
and  most  exact  is  the  macula  lutea  and  its  fovea  centralis.  The 
anatomical  layer  designed  to  be  impinged  upon  by  a  distinct  image 
is  the  membrane  of  Jacobson,  the  layer  of  rods  and  cones.  As  only 
the  cones,  and  no  rods,  are  found  in  the  fovea  centralis,  it  is  the 
point  where  objects  are  fixed.  Hence  it  must  be  held  that  the  cones 
are  the  specific  elements  of  the  retina  that  are  designed  to  make  the 
individual  perceive  a  luminous  impression  precisely.  Nevertheless, 
the  field  of  vision,  though  indistinct  toward  its  periphery,  is  very 
much  enlarged. 


VISION.  721 

The  luminous  impression  consists  of  the  vibrations  of  the  lumi- 
nous ether  which  stimulate  the  outer  portion  of  the  rods  and  cones. 
In  them  there  is  produced  a  molecular,  mechanical  change,  or  dis- 
turbance. Whenever  the  layer  of  rods  and  cones  is  stimulated,  the 
excitation  is  propagated  from  without  inward  to  all  of  the  retinal 
elements. 

Von  Kries  holds  that  the  cones  alone  have  the  power  to  per- 
ceive colors  (day  vision),  whilst  the  rods  are  sensitive  only  to  light 
and  darkness.  The  rods,  by  their  adaptability  in  the  dark  through 
the  regeneration  of  their  visual  purple,  form  the  special  apparatus 
for  vision  in  dim  lights  (night  vision).  The  various  elements  are 
connected  by  fibers,  and,  finally,  by  the  optic  nerve  with  the  brain. 

Physiology  of  the  Eye. 

The  study  of  the  phenomena  of  the  eye  may  be  divided  into 
four  parts:  (1)  dioptrics,  {2}  accommodation,  (3)  imperfections  and 
corrections,  and  (4)  vision  icith  both  eyes. 

Dioptrics. — The  eye  has  previously  been  mentioned  as  being  like 
a  camera  obscura.  If  a  small  opening  exist  in  the  shutter  of  a  dark 
room  the  rays  of  light  from  tlie  outside  passing  through  the  opening 
will  form  an  inverted  image  of  the  external  object  upon  the  opposite 
wall  of  the  chamber.  However,  unless  the  opening  be  very  small, 
the  image  will  be  blurred  and  indistinct.  These  latter  qualities  will 
be  due  to  overlapping  of  rays  of  light  from  various  points  of  the 
object.  If  the  opening  be  small  enough  the  overlapping  rays  will 
be  cut  off  and  a  distinct  image  be  formed.  Should  a  convex  lens  be 
interposed  in  the  path  of  the  rays  of  light  the  opening  may  be  very 
considerably  enlarged,  and  yet  the  various  rays  be  brought  to  a  focus 
so  that  diffused  images  will  be  prevented. 

The  camera  obscura  is  popularly  known  to-day  in  the  form  of 
the  photographic  camera.  The  latter  consists  of  a  box  blackened  on 
the  interior  to  prevent  reflection  from  the  walls.  In  front  is  a  short 
tube  which  contains  achromatic  lenses.  In  the  back  wall  of  the 
camera  is  found  a  ground-glass  plate  upon  which  the  image  formed 
by  the  lens  is  focused.  If  the  camera  be  so  adapted  that  parallel 
rays  falling  upon  the  lens  are  focused  upon  the  ground-glass  plate, 
then  divergent  rays  must  have  their  focal  point  behind  the  plate. 
Should  the  plate  be  moved  backward  or  forward  the  focal  point  can 
be  made  to  coincide  with  the  conjugate  focus  of  the  rays  diverging 
from  the  object. 

46 


•^22  PHYSIOLOGY. 

Spherical  Aberration,  which  interferes  with  distinctness,  is 
gotten  rid  of  by  cutting  off  outside  rays.  In  the  camera  this  point 
is  accomplished  l)y  the  insertion  of  a  diaphragm  through  a  slit  in 
the  lens-tube.  The  diaphragm  is  pierced  by  holes — a  larger  or 
smaller  one  being  used  according  as  the  light  is  feeble  or  strong. 

The  eye  may  be  very  aptly  compared  to  the  camera.  It  has  a 
small  opening  in  front  through  which  pass  the  rays  of  light.  The 
sclerotic  and  choroid  coats  form  its  walls.  The  refracting  lenses  are 
the  cornea,  aqueous  humor,  crystalline  lens,- and  vitreous  humor. 
They  all  tend  toward  the  accomplishment  of  the  same  end :  to  bring 
parallel  rays  of  light  to  a  focus  upon  a  sensitive  plate  (the  retina), 


Fig.   341. — Diagram  Illustrating  Spherical  Aberrations.      (Ganot.) 

The  rays  passing  through  the  edge  of  the  lens  have  a  shorter  focal 
distance  than  those  passing  nearer  to  the  center. 

there  to  form  a  real  inverted  image  of  the  object.  Last,  the  iris  with 
its  pupil  acts  as  a  diaphragm. 

Chromatic  Aberration. — The  edge  of  the  lens  of  a  camera 
represents  the  outer  angle  of  a  prism.  White  light  falling  upon  it  is 
decomposed  into  its  spectral  components.  Objects  seen  upon  the 
ground-glass  plate  have  an  iridescent  hue.  In  the  eye  this  trouble 
is  obviated  by  the  presence  of  the  iris  and  the  fact  of  the  edge  of 
the  lens  being  more  angular  and  less  curved. 

Visual  Angle. — It  is  usually  stated  to  be  the  angle  included 
by  the  lines  from  the  extreme  points  of  the  object  where  they  cross 
at  the  nodal  point.  The  apparent  size  of  the  object  depends  upon 
the  visual  angle.  Acuteness  of  vision  is  inversely  as  the  size  of  the 
visual  angle. 

Act  of  Accommodation. — AYlien  a  luminous  body  is  brought  too 
near  to  the  eye,  the  rays  which  pass  from  it  tend  to  come  to  a  focus 


VISION. 


723 


behind  the  retina.  In  this  way  circles  of  diffusion  form,  which 
would  prevent  the  appearance  of  a  distinct  image  if  a  special  appar- 
atus did  not  exist  for  the  purpose  of  modifying  the  degree  of  refrac- 
tion. This  modification  is  what  is  understood  by  the  term  accommo- 
dation. 

Mechanism  of  Accommodation. — The  ciliary  muscle,  when  it 
contracts,  causes  the  zone  of  Zinn  to  advance,  and  thus  diminishes 
the  tension  exercised  by  the  latter  upon  the  capsule  of  the  crystalline 
lens.     The  lens,  left  to  itself,  assumes  the  form  which  the  elasticity 


Fig.  342. — Schemo  of  Accommodation  for  Near  and  Distant  Objects. 
(Landois,  after  Helmholtz.) 

The  right  side  of  the  figure  represents  the  condition  of  the  lens  during 
accommodation  for  a  near  object  and  the  left  side  when  at  rest.  The  letters 
indicate  the  same  parts  on  both  sides;  those  on  the  right  side  are  marked  with 
a  stroke  (or  minute  mark).  A,  Left  half  of  lens.  B,  Right  half  of  lens.  C, 
Cornea.  S,  Sclerotic.  CS,  Canal  of  Schlemm.  VK,  Anterior  chamber.  J,  Iris. 
P,  Margin  of  pupil.  T',  Anterior  surface.  //,  Posterior  surface  of  lens.  R, 
Margin  of  the  lens.  F,  Margin  of  ciliary  processes,  a,  h.  Space  between  the 
two  former.  The  line  Z-X  indicates  the  thickness  of  the  lens  during  accom- 
modation for  a  near  object.  Z-Y,  the  thickness  of  the  lens  when  the  eye  is 
passive. 

of  its  fibers  naturally  gives  it  and  becomes  more  convex,  especially 
at  its  anterior  surface.  When  the  action  of  the  oculomotor  nerve 
ceases,  the  ciliary  muscle  is  relaxed,  the  ciliary  processes  become 
tense  and  make  traction  on  the  zone  of  Zinn,  which  in  turn  flattens 
the  lens  by  exerting  upon  it  a  traction  in  the  direction  of  its  equator. 
The  retina  follows  along  with  the  choroid  in  the  movement  of 
accommodation.  When  the  traction  of  the  ciliary  muscle  ceases 
relaxation  of  accouimodatiou  in  tliis  way,  the  border  of  the  retina, 
being  closely  attached  with  the  choroid,  is  stretched  and  irritated  by 
the  siulden  relaxation  of  accommodation  until  the  lens  flattens. 

These  locomotor  changes  of  the  choroid  may  generate  a  choroid- 
itis, especially  in  the  production  and  progress  of  myopia.  Atropine,  by 


724  PHYSIOLOGY. 

paralyzing  the  oculomotor  nerve  and  thus  the  ciliary  muscle,  has  a 
very  favorable  influence  by  putting  the  affected  membranes  at  rest. 

The  suspensory  ligament  (zone  of  Zinn)  is  not  a  membrane,  but 
an  agglomeration  of  fibers  of  the  nature  of  connective  tissue.  They 
originate  partly  at  the  ora  serrata  from  the  intervals  between  the 
ciliary  processes,  and  a  few  of  them  from  the  ciliary  processes 
themselves. 

Accompanying  the  act  of  accommodation  is  a  contraction  of  the 
pupil,  which  dilates  when  the  accommodation  relaxes,  and  a  conver- 
gence of  the  eyeballs  due  to  a  contraction  of  the  internal  recti. 

The  range  of  accommodation  is  as  follows: — 


BARS 

Range  of 
Accommodation 

10 

14  D. 

15 

12 

20 

10 

25 

8.0 

.30 

7 

35 

5.5 

40 

4.5 

Years 

Rangk  of 
Accommodation 

45 

3.5 

50 

2.5 

55 

1.75 

60 

1. 

65 

0.75 

70 

0.25 

75 

0. 

This  table  shows  that  the  power  to  accommodate  diminishes 
rapidly  and  considerably  as  we  become  older.  This  is  due  to  the 
decreasing  elasticity  of  the  crystalline  lens.  The  crystalline  lens 
commences  early  to  change  its  physical  constitution  and  becomes 
more  rigid,  whilst  our  other  bodily  forces  are  in  a  state  of  progres- 
sive development. 

In  what  may  be  regarded  as  the  normal,  or  so-called  emmetropic, 
eye,  the  near  point  of  accommodation  is  about  five  inches.  The  far 
limit,  for  all  practical  purposes,  is  from  200  feet  up  to  an  infinite 
distance.     In  this  eye  the  range  of  distinct  vision  has  wide  latitudes. 

In  the  myopic,  or  short-sighted,  eye  the  near  point  is  two  and 
one-half  inches  from  the  cornea.  The  far  limit  is  at  a  variable,  but 
not  very  great,  distance.  The  range  of  vision  in  this  eye  is  very 
limited.  In  this  the  rays  of  light  are  brought  to  a  focus  in  front 
of  the  retina. 

In  the  hypermetropic,  or  far-sighted,  eye  rays  of  light  coming 
from  an  infinite  distance  are,  in  the  passive  state  of  the  eye,  brought 
to  a  focus  behind  the  retina.     The  near  point  is  some  distance  away. 

The  presbyopic,  or  long-sighted,  eye  of  aged  persons  resembles 
the  hypermetropic  eye,  but  differs  in  so  far  that  the  former  is  an 
essentially  defective  condition  of  the  mechanism  of  accommodation. 

There  are  two  changes  which  occur  when  we  accommodate  for 
near  objects:    one  is  that  the  pupil  contracts  to  cut  off  divergent 


VISION. 


725 


rays;  the  other  is  a  change  of  curvature  of  the  lens.  The  ciliary 
muscle  is  the  motive  power  of  accommodation.  Its  paralysis  renders 
accommodation  impossible.  The  oculomotor  innervates  the  ciliary 
muscle.  Its  paralysis  by  atropine  produces  both  dilatation  of  the 
pupil  and  inability  to  accommodate. 

To  correct  anomalies  of  refraction  it  is  necessary  to  use  lenses. 
These  are  transparent  media  which  seem  to  refract  rays  of  light 


Fig.   343. — Refraction  of   Pai-allel   Rays  of   Light  in   Emmetropia    (E), 
Hypermetropia   {H) ,  and  Myopia   {M) .     ( Ball. ) 

passing  through  them.  They  have  curved  surfaces.  The  direction 
which  the  rays  take  on  emerging  from  the  medium  depends  upon 
the  nature  of  the  curvature.  The  chief  forms  of  lenses  are  convex 
and  concave;  convex  lenses  may  be  doubly  convex,  plano-convex,  or 
concavo-convex.  A  concave  lens  may  have  equivalent  features.  A 
convex  lens  converges  the  rays  of  light;  a  concave  lens  diverges  the 
rays  of  light.  In  myopia  a  concave  lens  is  used;  in  hypermetropia 
and  presbyopia,  a  convex  lens. 


726 


PHYSIOLOGY. 


Astigmatism  is  n  defect  of  refraction  due  to  a  want  of  S3'mmetry 
in  the  refracting  media  of  the  eye.  The  result  of  this  is  that  the 
rays  of  light  passing  through  the  lens  are  not  l)rought  to  a  focus  at 
the  same  point.  This  want  of  symmetry  is  usually  in  the  cornea, 
but  may  he  in  the  lens.  To  remedy  this  defect  we  use  a  lens  called 
a  cylinder  to  level  up  the  curvature  of  one  of  the  meridians  of  the 


Fig.  .344. — Different  Kinds  of  Lenses.      (Ganot.  ) 

A,  Double  convex.  B,  Plano-convex.  C,  Converging  concavo-convex.  D, 
Double  concave.  E,  Plano-concave.  ¥,  Diverging  concavo-convex.  C  and  F  are 
also  called  meniscus  lenses. 


cornea  to  correspond  to  the  curvature  of  the  others.  Cylinders  have 
no  curvature  in  one  axis,  but  more  or  less  considerable  curvature  in 
the  opposite  axis  in  correspondence  with  the  degree  of  astigmatism 
that  has  to  be  corrected. 

Lenses. — Lenses  are  arranged  according  to  their  focal  distance 
in  inches,  and,  as  the  unit  was  taken  as  one  inch,  all  weaker  lenses 


r    G 


^^e-^) 


Fig.   345. — Refraction  of  Rays   in  Regular  Astigmatism.      (Ball.) 

were  expressed  in  fractions  of  an  inch.  However,  Bonders  made 
the  standard  in  lenses  of  a  focal  distance  of  one  meter,  and  this  unit 
he  called  a  dioptre.  Thus  the  standard  in  a  weak  lens  and  the 
stronger  lens  are  multiples  of  these.  Hence  a  lens  of  two  dioptres 
equals  one  of  about  twenty  inches'  focus. 

Purktn.te-Sanson's  Images.— If  you  place  a  lighted  candle  in 
front  of  the  eye  of  a  person,  three  images  of  the  flame  are  seen. 
One,  which  is  direct,  small,  brilliant,  and  comes  from  the  anterior 


VISION.  727 

surface  of  the  cornea;    another,  which  is  in  the  middle,  is  direct, 

larger,  hut  not  so  hright,  and  is  due  to  the  anterior  surface  of  the 

lens,  which  acts  as  a  convex  mirror;    and,  finally,  a  third  image, 

small,  inverted,  and  brilliant,  due  to  the  posterior  surface  of  the 


Fig.  34G. — Uiagrani  Showing  Refraction  by  a  Double  Convex  Lens. 

(  Gaxot.  ) 

The  incident  ray  (,L-B)  is  refracted  at  the  points  of  incidence  (B),  and 
emergence  (D),  toward  the  axis  (M-N-A),  which  it  cuts  at  F. 

lens,  which  also  acts  as  a  convex  mirror.  If  the  person  experimented 
on  looks  fixedly  at  objects  placed  at  different  distances,  the  only 
change  in  the  three  reflections  which  we  mentioned  will  be  found  to 
take  place  in  that  caused  by  the  anterior  surface  of  the  crystalline 
lens.  This  fact  leads  to  the  conclusion  that  the  phenomena  of 
accommodation  are  dependent  upon  a  change  in  the  anterior  surface 
of  the  crvstalline  lens. 


Fig.   347. — Concave  Lens   Diverging   Parallel   Rays   of    Light. 
(Laiiousse.  ) 

In  the  act  of  accommodation,  when  the  candle  is  brought  nearer 
the  eye,  the  image  due  to  the  anterior  surface  of  the  crystalline  lens 
becomes  smaller  because  the  lens  becomes  more  convex. 

The  form  and  variations  in  form  of  the  dioptric  surfaces  of  the 
eye  can  be  measured  by  Helmholtz's  ophthalmometer  and  the  phako- 
scope  of  Helmholtz. 


'28 


PlIVSIOLOaY. 


Blind  Spot. — ]\[iU"ri()llc's  cxpcriiiiciit  jji-ovcs  Hint  at  the  en- 
trance ot  the  o])tie  nerve,  w  Ihtc  rods  and  cones  ai'e  not  lo  Ix;  tound, 
the  spot  is  a  blind  spot. 

Thus:  make  a  cross  and  a  cireh'  about  tliree  inches  a])art  upon 
])apcr.     With   the   right   eve    view   the   cross,   keeping  the   k'ft   eye 

12  3  12  3 


A  B 

Fig.  34S. — Piirkinje-Sanson  Images.      (Ball.) 

A,  In  the  absence  of  accommodation.  IS,  In  accommodation.  1,  Reflection 
from  the  cornea.  2,  From  the  anterior  surface  of  the  lens.  3,  From  ihe  poste- 
rior surface  of  the  leas. 

closed.  Hold  the  paper  about  a  foot  from  the  eye,  when  both  cross 
and  circle  will  be  visible.  Let  the  paper  be  gradually  brought  nearer 
the  eye,  keeping  the  right  eye  steadily  fixed  on  the  cross.  At  a  cer- 
tain moment  the  circle  will  disappear,  and  that  time  is  when  the 
image  of  the  circle  falls  upon  the  optic  nerve  entrance. 


+ 


Fig.   349. — Diagram   to  Sliow   tlie   Blind   Spot  in  tlie   Visual   Field. 

(Ball.) 

The  minimum  visual  angle  is  fifty  seconds;  below  this  limit  the 
extreme  points  of  an  object  are  no  longer  separate  and  but  one  point 
is  perceived.  The  minimum  visual  angle  corresponds  to  a  retinal 
image  of  about  .004  millimeter,  which  is  nearly  the  diameter  of  one 
of  the  cones  of  the  retina. 

AcuTENESS  OF  VisiON. — Acutcness  of  vision  is  in  inverse  ratio 
to  the  visual  angle.  It  diminishes  as  the  later  increases.  In  favor- 
able conditions,  bodies  having  a  diameter  of  V^^  to  Vioo  of  an  inch 
are  perceived  by  the  naked  eye. 


VISION. 


729 


Circles  of  Diffusion. — When  rays  of  light  proceeding  from  a 
luminous  object  do  not  come  to  a  focus  directly  on  the  retina,  the 
image  is  no  longer  distinct,  and  circles  of  diffusion  appear  about  it. 
In  the  normal  condition,  the  luminous  rays  passing  to  a  point  of  the 
retina  through  the  pupil  form  a  cone,  the  base  of  which  is  at  the 
pupil  and  the  apex  at  the  retinal  focus.     But  if  the  focus  be  placed 


Fig.  350. — Scheiner's  Experiment — an  experiment  to  determine  the 
minimum  distance  of  distinct  vision. 

in  front  of  or  behind  the  retina,  the  latter  intersects  the  bundle  of 
rays  so  that,  instead  of  a  point  on  the  retina  corresponding  to  one 
on  the  luminous  object,  we  have  a  circle  formed.  The  different 
points  of  the  retina  will  be  intersected  by  rays  coming  from  various 
parts  of  the  object,  and  the  image  in  this  way  becomes  blurred  and 


Fig.  351. — Diagram  to  show  that  the  visual  angle  and  size  of  the  retinal 
image  vary  with  tlie  distance  of  the  object  from  the  eye.     (Ball.) 

The  image  of  S-B  is  seen  at  0.8.  under  the  angle  g,  and  the  image  of 
T.C.   is  seen  at  I-W  under  the  angle  Ma. 

loses  its  distinctness.  The  existence  of  these  circles  of  diffusion 
explains  why  it  is  that  we  cannot  at  the  same  time  see  clearly  objects 
which  are  placed  at  different  distances  from  the  eye.  Their  size 
varies  with  the  distance  of  the  focus  from  the  retina,  being  larger 
as  the  distance  is  greater,  and  also  with  the  size  of  the  pupil,  con- 


730  PHYSIOLOGY. 

trad  ion  of  which  narrows  tlic  cone  ol'  luminous  rays  and  conse- 
quently the  circles  of  diffusion. 

SciiEiNEK^s  Experiment. — A  card  is  taken  in  which  two  small 
holes  are  placed  close  togethePo  The  card  is  held  close  to  the  eye, 
and  in  front  of  it  a  needle  is  held.  When  you  move  the  needle 
nearer  the  card,  and  then  farther  from  it,  a  position  is  found  where 
it  is  distinctly  seen.  If  it  be  brought  slightly  nearer,  the  needle 
appears  double,  and  you  obtain  the  double  image.  The  explanation 
is  easily  seen  from  the  diagram.  Fig.  350. 

e  f  represent  the  holes  in  the  card,  a  the  point  of  the  needle,  h 
a  lens,  and  m  n  I  a  screen  at  varying  distances  from  it.     With  the 

TS 


NA 

Fig.  352. — Diagram  Showing  tlip  Corneal  Axis,  IJ-E;  the  Optic 
Axis,  0-A;  the  Visual  Line,  R-Y ;  the  Line  of  Fixation,  R-J ;  and 
the  Three  Angles.     (Ball.) 

The  angle  between  U-E  and  the  visual  line  R-Y  is  the  angle  Alpha,  averaging 
5  degrees.  The  angle  between  the  optic  axis  (O-.l)  and  the  line  of  regard  {R-J) 
is  the  angle  gamma.  The  angle  between  the  optic  axis  (0-A)  and  the  line  of 
vision  (R-Y)  is  the  angle  beta.     T8,  Temporal  side.    NA,  Nasal  side. 

screen  at  n,  a  distinct  single  image  of  the  needle  is  perceived,  because 
the  rays  e  and  /  coincide  and  are  focused  at  n  n.  At  the  position 
m  the  image  is  blurred  and  double  because  the  rays  from  e  do  not 
coincide  with  those  from  f;  while  at  I  the  image  is  also  double 
and  blurred  because  the  rays  are  intercepted  after  they  have  diverged 
from  their  focus.  Let  h  represent  the  refractive  media  of  the  eye, 
and  m  n  the  retina. 

The  Optic  Axis. — This  is  a  line  which  passes  through  the 
nodal  point  and  the  center  of  the  cornea.  If  prolonged  backwards, 
it  falls  upon  the  retina  on  the  inner  side  of  the  yellow  spot. 

The  Visual  Line. — The  visual  line  joins  the  macula  lutea 
with  the  point  on  which  the  eye  is  fixed.     It  passes  through  the  cor- 


VISION. 


731 


nea  a  little  to  the  inner  side  of  its  center,  and  therefore  forms  an 
angle  with  the  optic  axis,  which  is  termed  the  angle  alpha,  which 
normally  does  not  exceed  -l  to  5  degrees. 

Horopter. — The  horopter  represents  all  those  points  of  the 
outer  world  from  which  rajs  of  light  passing  into  both  eyes  fall  on 
identical  points  of  the  retina,  the  eyes  being  in  a  certain  position. 

It  is  a  circle  of  which  the  chord  is  formed  by  the  distance 
between  the  point  of  decussation  of  the  rays  of  light  in  the  eye.     Its 


size  is  determined  by  the  position  of  the  two  eyes  and  the  point 
towards  which  their  axes  converge.  All  objects  not  found  in  the 
horopter,  or  which  do  not  form  an  image  on  corresponding  points  of 
the  retina,  are  seen  double. 

IxvERTED  Image  of  Objects. — The  rays  proceeding  from  the 
surface  of  luminous  bodies  above  the  optic  axis  cross  in  the  eye  so 
as  to  be  brought  to  a  focus  below  the  axis,  and  mce  versa.  Thus  an 
inverted  image  is  formed  on  the  retina. 

The  Acuteness  of  Vision  is  tested  by  Snellen's  types.  It  has 
been  found  out  that  square  letters  which  have  limbs  and  parts  equal 


732 


PHYSIOLOGY. 


in  breadth  to  two  of  the  height  of  the  letters  are  distinctly  legible 
to  a  normal  eye  under  an  angle  of  live  minutes.  These  letters  arc 
numbered,  the  numbers  expressing  in  meters  tlie  distance  at  which 
the  letter  can  be  seen  under  an  angle  of  five  minutes.  The  eye  is 
tested  with  letters  smaller  and  smaller  at  the  same  distance  from 
the  eye,  (!  meters.     Suppose  No.  6  type  is  thus  seen;    then  Ve  =  l, 


Fig.  .354.— The  Visual  Angle. 


If  Xo.  <S  is  only  seen  at  6 
or  three-fourths  of  that  of 


the  acuteness  of  vision  of  a  normal  eye. 
meters,  then  the  acuteness  of  vision  is  ^/ 
the  normal  eye. 

Duration  of  Eetinal  Stimulation. — Light  impresses  the  re- 
tina, but  the  excitation  of  it  does  not  cease  immediately  with  the 
disappearance  of  the  luminous  vibrations.  Indeed,  they  persist  for 
a  certain  time,  about  one-eighth  of  a  second:  that  is,  proportional 
to  the  intensity  of  the  excitation.     Upon  a  disc  black  and  white  sec- 


Fig.  .355. — Optogram  on  the  Rabbit's  Retina  of  a  Window  Four 
Meters  Distant.  (Kuhne. )  (From  Tigerstedt's  "Human  Physiology," 
copyright,  1906,  by  D.  Appleton  and  Company.) 

b,  6,  White  streak  of  nerve-fibers,  and  yellow  spot  in  its  center. 

tions   are   alternately   painted.     When   the  disc  is  made  to   rotate 
rapidly  the  disc  appears  neither  black  nor  white,  but  gray. 

Visual  Pueple,  or  Rhodopsin. — The  outer  part  of  the  rods 
contains  a  reddish  coloring  matter  which  is  called  visual  purple. 
The  cones  do  not  have  any.  This  coloring  matter  must  be  kept  in 
the  dark,  for  it  bleaches  the  moment  light  strikes  it.     But  the  color 


VISION.  733 

will  return  if  the  eye  is  again  brought  into  a  dark  chamber.  The 
bile  acids  extract  the  coloring  matter  from  the  retina.  The  visual 
purjole  is  a  product  of  melanin  or  fuscin. 

Kiihne  has  shown  that  an  image  or  optogram  of  an  object  may 
be  fixed  on  the  retina  by  plunging  it  into  a  -f-per-cent.  alum  solution 
immediately  after  death. 

The  visual  purple  increases  in  the  dark,  and  is  supposed  to  ren- 
der the  rods  more  irritable  in  the  dim  light  of  the  evening.  Hence 
Van  Kries  has  put  forth  the  theory  that  the  more  abundant  rods  in 
the  peripheral  field  of  the  retina  are  chiefly  fitted  for  vision  at  night, 
whilst  the  cones  are  chiefly  for  day  vision  in  strong  light. 


Fig.  356. — Diagram  Illustrating  the  Decomposition  of  White  Light 
into  the  Seven  Colors  of  the  Spectrum  in  Passing  Through  a  Prism. 
(  Beclard.  ) 

r.  Red.    0,  Orange.    ;,  Yellow,     v,  Green.     6,  Blue,     i.  Indigo.     i(,  Violet. 

Color-vision. — White  light  is  composed  of  rays  of  different  re- 
frangibility  by  reason  of  the  different  length  and  duration  of  the 
luminous  rays.  These  various  rays  falling  upon  the  retina  determ- 
ine in  the  individual  different  sensations  wliich  correspond  to  the 
colors.  To  decompose  white  light  into  its  different  colors,  the  prism 
is  used.  A  ray  of  white  light  upon  issuing  from  the  prism  presents 
the  spectrum.  That  is,  there  emerge  the  principal  simple  colors 
from  the  most  to  the  least  refrangible.  They  are  violet,  indigo,  blue, 
green,  yellow,  orange,  and  red.  Each  primary  color  cannot  be  fur- 
ther decomposed,  but  all  can  be  reunited  by  a  biconvex  lens  so  that 
white  light  will  result  again.  The  ultra-red  (thermal)  and  ultra- 
violet (chemical)  rays  do  not  make  any  impression  upon  the  retina. 


734 


PHYSIOLOGY. 


The  former  do  not  pass  through  the  media  of  the  eye,  since  by  vibra- 
tion-rates beneath  435,000,000,000  per  second  the  retina  is  not  stim- 
ulated; the  latter  color  produces  no  sensation,  since  to  vibration- 
rates  above  764,000,000,000  per  second  the  retina  is  insensible. 

Sensations  op  Color. — In  the  production  of  the  sensations  of 
color  there  are  three  chief  factors:  tone,  saturation,  and  intensity. 
The  tone  of  the  color  depends  upon  the  number  of  vibrations  of  the 
ether.  A  color  is  said  to  be  saturated  when  it  does  not  contain  any 
white  light.  The  simple  colors  of  the  spectrum  are  saturated.  The 
intensity  of  color  depends  upon  the  amplitude  of  the  vibrations. 


Fig.  357. — Wools  for  the  Detection  of  Color  Blindness.      (Oliver.) 


Loss  of  Color-vision,  or  Daltonism. — Young  stated,  as  the 
explanation  of  color-vision,  that  all  the  colors  were  referable  to  three 
fundamental  sensations:  those  of  red,  green,  and  violet.  Corre- 
sponding to  the  three  sensations  excited  by  these  three  colors  were 
three  kinds  of  retinal  fibers,  stimulation  of  which  gives  rise  to  sen- 
sations of  red,  green,  and  violet.  It  is  also  supposed  that  white  light 
stimulates  these  fibers  with  difl^erent  degrees  of  activity  according  to 
the  length  of  the  wave.  The  longest  wave  acts  most  on  the  fibers 
which  respond  to  the  red  color,  the  medium  wave  on  the  fibers  which 
respond  to  green,  and  the  shortest  wave  on  the  violet.  Helmholtz 
adopted  the  theory  of  Young.  It  is  also  supported  by  the  facts  of 
color-blindness,  in  which  there  is  an  inability  to  distinguish  one  or 
more  of  the  fundamental  colors.  The  commonest  form  of  color- 
blindness is  that  in  which  red  is  the  invisible  color,  and  in  the  com- 


VISION.  735 

pound  colors  in  which  red  enters  the  complementary  color  alone  is 
visible,  white  appearing  as  bluish  green.  Another  theory  of  color- 
vision  is  that  of  Hering.  The  six  sensations  of  color  readily  fall 
into  three  pairs,  the  members  of  each  pair  having  similar  relation- 
ship. White  and  black  naturally  go  together,  the  one  being  antagon- 
istic of  the  other.  According  to  Hering,  the  retina  is  undergoing 
metabolic  changes,  and  he  supposes  there  are  three  distinct  visual 
substances  which  are  undergoing  anabolism  and  catabolism.  When 
breaking  down,  or  catabolism,  is  in  excess  of  the  building  up,  or 
anabolism,  we  have  a  sensation  of  white;  when  upbuilding  predomi- 
nates, we  have  black. 

Anabolism  of  the  visual  substances  by  the  rays  of  light  produces 
green,  blue,  and  black;  catabolism  of  these  visual  substances  pro- 
duces white,  red,  and  yellow. 

(  White  is  eatabolic  C  Red  is  catabolic 

1.  ^  and  2.  ^  and 

I   Black  is  anaboli..  I   (ireen  is  anabolic. 

j   Yellow  is  catabolic 
3.  <  and 

I    Blue  is  anabolic. 

In  applying  this  theory  to  colnr-ljlindness  it  must  be  assumed 
that  those  who  are  red-blind  want  the  red-green  visual  substance; 
they  have  only  the  black-white  and  yellow-blue  visual  substance  in 
the  retina. 

According  to  the  Young-Helmholtz  theory,  there  is  a  defect  cor- 
responding to  the  three  color-perceiving  fibers.  According  to  this 
theory  color-blindness  is  of  four  kinds:  red,  green,  and  violet,  and 
complete  blindness  to  colors.  In  the  Hering  theory  the  kinds  are: 
(1)  comjilete,  (2)  blue-yellow,  (3)  red-green,  and  (4)  incomplete  color- 
blindness. 

Color-blindness  is  also  called  Daltonism,  after  Dalton,  a  Quaker, 
who  first  described  it.  The  percentage  of  color-blindness  among  per- 
sons is  al)out  -i  per  cent,  in  males,  and  1  per  cent,  in  females;  and 
among  Quakers  4Vo,  because  for  generations  they  have  worn  drabs. 
The  disease  is  hereditary.  The  cones  in  color-vision  are,  according 
to  Van  Kries,  for  the  perception  of  color,  whilst  the  rods  are  for  the 
perception  of  light  and  darkness. 

CoMPLEiiEXTARY  CoLORS. — Those  colors  are  complementary 
which  when  mixed  together  produce  white.  The  following  table 
gives  the  complementary  colors  of  the  spectrum: — 


736 


PHYSIOLOGY. 


Red — greenish  blue. 
Orange — Prussian  blue. 
Yellow — indigo-blue. 


Greenish  yellow — violet. 
Green — purple. 


Green  alone  has  no  complementary  color  in  the  spectnim. 
gives  a  white  color  with  the  compound  color  purple. 


It 


Fig.  358. — Diagram  Illustrating  Irradiation.      (Stirling.) 

If  this  diagram  is  held  some  distance  from  the  eye,  especially  if  not  exactly 
focused,  the  white  dot  will  appear  larger  than  the  black,  though  both  are  of 
exactly  the  same  size. 

Irradiation. — This  is  a  phenomenon  which  is  observed  when 
looking  at  a  strongly  illuminated  object  upon  a  dark  background; 
the  object  appears  larger  than  it  really  is.  Thus,  of  two  rings  of 
equal  size,  one  white  on  black,  the  other  black  on  white,  the  former 
appears  larger  than  the  latter.  Irradiation  is  due  to  imperfect 
accommodation.     Here  the  margins  of  an  object  are  projected  upon 


CT  Z 


Fig.  359. — Diagram  to  show  ( 1 )  the  primary  position  of  the  right 
eye;  (2)  the  eye  turned  upward  and  inward,  and  (3)  downward  and 
outward.      (  Ball.  ) 

er.   External   rectus,     ir,    Internal    rectus,     so,   io,    Superior  and   inferior 
oblique,    sr,  ifr,  Superior  and  inferior  recti. 

the  retina  in  circles  of  diffusion  and  the  brain  tends  to  increase  the 
ill-defined  margin  to  those  parts  of  the  visual  image  which  are  most 
prominent  in  the  image  itself.  What  is  bright  seems  larger  and 
overcomes  what  is  dark.  Black  clothes  make  one  appear  to  be  much 
smaller  than  light  clothes.  A  short  person  would  look  taller,  and  a 
fat  person  would  look  thinner,  dressed  in  vertical  stripes. 


VISION. 


737 


After-images. — When  a  bright  light  is  thrown  on  the  eye  and 
then  suddenly  put  out,  there  remains  for  a  short  time  an  impression 
of  the  same  light,  as  though  the  retinal  molecules  still  continued  to 
vibrate  from  the  light  stimulus.  This  is  a  positive  after-image. 
AVhen  the  eye  has  received  a  stimulus  for  some  time,  the  sensation 
■which  follows  the  withdrawal  is  of  a  different  kind,  and  you  have  a 
negative  after-image,  which  is  due  to  exhaustion  of  the  retinal  cells. 
For  instance,  if  you  look  at  a  red  color  for  some  time  and  the  eye 
afterward  is  focused  on  a  white  ground,  the  negative  after-image  is 
a  greenish-blue;  that  is,  the  color  of  the  negative  image  is  comple- 
mentary to  that  cf  the  object. 


Fig.  300. — Muscles  Associated  in  Moving  the  Eyeballs  in  the  Directions 
Indicated  by  the  Arrows.      (Ball.) 

Phosphenes. — If  the  retina  he  pricked,  compressed,  or  twitched 
by  any  sudden  movement,  an  impression  of  light  will  be  produced. 
The  same  effect  follows  the  use  of  electricity.  Hence  the  retina  is 
an  essentially  sensitive  membrane.  No  matter  by  what  cause  its 
sensibility  be  excited,  it  always  gives  rise  to  the  subjective  phe- 
nomenon of  a  luminous  sensation. 

Vision  with  Both  Eyes. — The  study  of  phenomena  bearing  upon 
this  subject  comprises:  (1)  movements  of  the  eyes,  (2)  litwcular  vision, 
and  (3)  the  advantages  of  sight  ivitli  loth  eyes. 

MovEMEN^TS  OF  THE  Etes. — The  eyeball  may  be  considered  as 
an  articulated  spherical  globe  which  turns  upon  three  axes  that  cross 
each  other.  Six  voluntary  muscles  affect  the  three  rotations  of  the 
eye.  The  rectus  internns  and  externus,  when  acting  alone,  turn  the 
eye  from  side  to  side.     The  superior  and  inferior  recti  give  to  the 

47 


738 


PHYSIOLOGY. 


ocular  sphere  an  up-and-down  movement.     The  superior  or  inferior 
oblique  muscle,  acting  alone,  gives  the  eye  an  oblique  movement. 


A    X 


Paralysis  of  right 
external  rectus. 


Paralysis  of  right 
iateriial  rectus. 


Paralysis  of  right 
sujierior  rectus. 


/ 


Paralysis  of  right 
inferior  rectus. 


Paralysis  of  right 
superior  oblique. 


Paralysis  of  right 
inferior  oblique. 


Fig.  301. — Positions  of  Images  in  Ocular  Paralyses.     (Ball.) 
The  true  image  is  black,  the  false  is  red. 

Coordinated  Movements. — The  two  eyes  always  present  coordi- 
nated movements  in  order  to  maintain  the  parallelism  or  conver- 
gence of  the  two  visual  lines.  The  visual  line  is  that  line  which 
passes  between  the  object,  center  of  the  pupil,  and  center  of  rota- 
tion of  the  ocular  glolje.  For  accommodation  at  a  distance  the  two 
visual  lines  are  parallel.  In  accommodation  for  near  objects  the 
lines  are  convergent. 


Pig.  3G2. — Capsule  of  Tenon.     (Ball,  after  Merkel.) 

So  long  as  the  muscles  of  the  eyeball  are  normal  in  function 
their  movements  are  in  cooordination.  Should  one  or  more  become 
paralyzed  or  seized  with  spasm,  then  proper  parallelism  and  conver- 


VISION. 


739 


gence  are  lost.  Strahismus  will  then  be  present  and  the  object 
looked  at  will  appear  double:    diplopia. 

Stevens  has  given  a  number  of  terms  for  the  deviation  of  the 
visual  axis  of  nonparalytic  origin.  Thus  orthophoria  is  a  condition 
of  muscular  equilibrium  of  the  eyeballs  with  the  least  nervous  effort. 
Esophoria  is  a  tending  of  the  visual  lines  inwards.  Exophoria  is  a 
tending  of  the  visual  lines  outward.  .Hyperphoria  is  a  tending  of 
the  visual  lines  of  one  eye  in  a  direction  above  its  fellow. 

The  innervation  of  the  muscles  of  the  eye  is  derived  from  the 
third,  fourth,  and  sixth  pairs  of  cranial  nerves. 


Fig.   3G3. — Diagram  Illustrating  Binocular   Vision.      (Beclard.) 

The  lines  from  the  object  indicate  that  rays  from  the  back  of  the  book 
fan  on  coincident  points  of  the  retina,  wh'le  each  eye  further  has  a  special  field 
of  vision. 

BixocuLAE  Vision'. — Looking  into  space  with  one  eye,  one  sees 
an  almost  circular  field.  "With  the  one  eye  he  can  look  toward  the 
opposite  side  as  far  as  the  root  of  the  nose  permits.  If  he  opens  the 
other  eye  the  visual  space  becomes  much  more  extended  in  a  trans- 
verse direction,  but  corresponding  to  a  monocular  field,  since  the  two 
monocular  fields  are  superposed. 

"Why  should  any  point  or  object  be  seen  single  and  not  double, 
when  the  point  forms  not  one,  but  two  images  upon  the  retinre? 
The  explanation  accepted  is  that  the  images  are  as  two  correspond- 
ing identical  points.     These  points  are  ?o  related  to  one  another  that 


740 


PHYSIOLOGY. 


the  sensations  from  each  arc  lilondcd  into  one  perception.  The 
movements  of  the  eyeballs  are  also  adapted  to  bring  the  image  of 
the  object  to  fall  upon  identical  parts.  The  law  results  that  if  one 
luminous  ])oint  simultaneously  impresses  two  identical  points,  it  must 
be  seen  as  single  and  not  double.  The  two  images  are  referred  to 
one  point  in  space  and  they  produce  in  the  individual  only  one 
impression. 

The  muscles  concerned  in  the  movements  of  the  eyeball  are  as 
follows : —  t 


Fig.  304. — Lacrimal  and  Meibomian  Glands,  the  latter  viewed  from 
the  posterior  surface  of  the  eyelids.  The  conjunctiva  of  the  upper  lid 
has  been  partially  dissected  off,  and  is  raised  so  as  to  show  the  Meibo- 
mian glands  beneath.     (Raymond,  after  Testut.) 

1,  Free  border  of  upper,  and  2,  free  border  of  lower  lid,  with  openings  of  the 
Meibomian  glands.  5,  Meibomian  glands  exposed,  and  6,  as  seen  through  con- 
junctiva. 7,  8,  Lacrimal  gland.  9,  Its  excretory  ducts,  with  10,  their  openings 
in  the  conjunctival  cul-de-Huc.     11,   Conjunctiva. 


Inward — Eectus  internus. 

Outward — Eectus  extemus. 

Upward — Rectus  superior,  obliquus  inferior. 

Downward — Rectus  inferior,  obliquus  superior. 

Inward  and  upward — Rectus  internus,  rectus  superior,  obliquus 
inferior. 

Inward  and  downward — Rectus  internus,  rectus  inferior, 
obliquus  superior. 

OutAvard  and  upward — Rectus  externus,  rectus  superior,  obliquus 
inferior. 


VISION. 


dowmvard — Kectus     externus, 


741 
rectus    inferior. 


Outward    and 
obliquus  superior. 

Stekeoscopic  Yisiox. — When  two  monocular  pictures  are  placed 
side  by  side,  and  viewed  by  the  two  eyes  respectively  through  the 
two  halves  of  a  convex  lens,  we  have  one  form  of  the  instrument 
called  the  stereoscope.     The  most  striking  results  are  produced  by 


l>'ig.  365. — Loring's  Ophthalmoscope. 

two  photographs  taken  at  the  same  time  by  two  cameras,  so  placed 
that  their  axes*  shall  form  the  same  angle  with  each  other  as  that 
which  the  axes  of  the  two  eyes  would  form  when  looking  at  the  same 
object.  "When  we  look  at  a  solid  object  near  l^y  with  l:)oth  eyes,  the 
right  eye  sees  farther  round  the  object  on  the  right  side,  and  the 
left  eye  farther  round  on  the  left  side.  These  two  slightly  different 
images,   when    compared   in   the  mind,   produce    the   perception  of 


742 


PHYSIOLOGY. 


solidity  or  depth,  since  experience  has  taught  us  that  those  objects 
only  which  have  depth  can  affect  the  eyes  in  this  way. 

The  photographs  are  slightly  different  from  each  other,  for  if 
they  were  identical  no  sensation  of  relief  will  ensue.  The  combina- 
tion of  the  dissimilar  images  furnished  by  the  two  eyes  is  a  mental 
act. 

0 


Fig.  .366. — Direct  Oplitlialmoscopy.      (Ball.) 

Lacrymal  Secretion. — Lately  it  has  been  shown  by  Landolt  that 
in  the  rabbit  and  the  monkey  secretory  nerves  of  the  lacrymal  gland 
run  in  the  facial  nerve.     These  nerves  leave  the  geniculate  ganglion 


Eve 


Lens 

Fig.  .367. — Indirect  Ophthalmoscopy. 


;  Ball.  ) 


and  enter  the  superficial  petrosal.  We  then  find  them  in  the  supe- 
rior maxillary  and  occasionally  in  the  ophthalmic.  He  believes  these 
fibers  run  in  the  glosso-pharyngeal  and  then  in  the  facial,  but  he  did 
not  locate  the  nucleus  from  which  they  arise.  Eserin  increases  the 
secretion  of  tears,  atropine  decreases  it. 


VISION. 


743 


Ophthalmoscope. — This  is  a  small  concave  mirror  by  means  of 
which  rays  of  light  are  directed  through  the  pupil  of  the  eye  so  that 
the  deep  parts  are  illuminated  and  made  visible.  There  is  a  hole 
in  the  center  of  the  mirror  through  which  the  examiner  looks.  But 
the  ophthalmoscope  may  be  used  with  or  without  lenses.  Without 
lenses  the  ophthalmoscope  gives  an  erect  image.  If,  however,  we 
use  a  convex  lens  over  the  central  aperture  of  the  ophthalmoscopic 
mirror  the  observer  sees  a  re-inverted  image.  If  a  concave  lens  is 
used  over  the  aperture  of  the  ophthalmoscopic  mirror  there  is  seen 
an  erect  image  considerably  magnified.  The  instrument  is  usually 
fitted  with  a  series  of  concave  and  convex  mirrors,  which  can  be 
revolved  in  front  of  the  central  aperture  of  the  mirror. 

If  the  observer  is  myopic  he  can  nse  the  concave  lenses  to  cor- 
rect his  myopia.  If  he  is  long-sighted,  he  corrects  it  by  means  of 
one  of  the  convex  lenses. 


Fig.  368. — The  McHardy  Perimeter.     (Brown.) 

If  the  eye  examined  be  short-  or  long-sighted,  the  retinal  image 
could  not  be  brought  into  focus  with  the  mirror  alone,  but  the 
examiner  can  adjust  his  concave  or  convex  disc,  as  the  case  may  be, 
and  find  a  lens  to  correct  the  short  or  long  sight  of  the  eye  examined. 

In  this  way  the  ophthalmoscope  may  be  used  to  measure  the 
degree  of  myopia  or  hypermetropia  of  the  eye  examined. 

Perimeter. — It  has  been  noted  that  by  the  peripheral  parts  of 
the  retina  a  person  can  observe  pretty  definitely  the  form  and  color 
of  objects.  To  determine  just  how  far  this  field  of  indirect  vision 
extends  in  exevx  direction  from  the  visual  axis  is  to  locate,  bv  the 


744 


PHYSIOLOGY. 


perimeter,  the  field  of  indirect  vision.     The  instrument  devised  for 
this  purpose  is  called  the  perimeter. 

With  the  perimeter  the  eye  is  made  to  view  a  fixed  point  from 
Avhich  a  ([uadrant  proceeds  so  that  the  eye  lies  in  the  center  of  it. 
Around  the  fixed  point  the  quadrant  rotates,  and  this  circumscrihes 
the  surface  of  a  hemisphere  in  the  center  of  which  the  eye  is  located. 
From  this  fixed  point  ohjeets  are  slid  on  semicircular  arms  and  are 


7< 

2M^ " 

X*^' 

/             y\                      )ir-^ ' 

/ 

1  /\  ^ 

,.      r,^      ;,■      rli       'A.       ^ITJ^ 

\\ 

jL?          TO 

\  \\  ^ 

\ 

/ 

\ 

izs\ 

J/ita- 

Blue 

Yellow.. 
R(2d_._ 

/s 

\'      \    ^-^\    y^ 

2S5' 

2SJ' 

Fig.  369. — Diagram  of  tlie  Normal  Visual  Field  for  White  and  Colors. 

(Jennings.) 

The   outer   continuous    line    indicates    the    limit   of   the   field    for   white,    and 
the  broken  lines  indicate  the  limits  of  the  color  fields. 


gradually  placed  more  toward  the  periphery  of  the  field  of  vision 
until  the  ohject  is  no  longer  noticed.  Then  hy  moving  the  semi- 
circular arm  in  different  meridians  of  the  field  of  vision  we  ohtain 
what  is  called  the  field  of  vision.  The  field  of  vision  is  more 
extended  below  and  to  the  outer  side.  It  is  narrowed  above  by  the 
brow;   below  by  the  cheek  and  the  nose. 


VISION. 


745 


Fig.  370. — Diagram  of  the  Visual  Tract.      (Ball. 


R.F.,  Right  visual  field.     L.F.,  Left  visual  field.    A'.  Nasal  side, 
side.     R.R.,   Right  retina.     L.R.,   Left  retina.     O.C,   Optic   chiasm 
nerve.      O.T.,    Optic    tract.      C.Q.,    Corpora    quadrigemina. 
geniculate  body.     T.O.,   Optic  thalamus.     C.C,   Corpus  ca.llosum 


T,  Temporal 

O.y.,    Optic 

Ex.G.B.,    External 


746 


PHYSIOLOGY. 


Visual  Field. — 'I'lie  Loundary  of  the  visual  field  of  white  light 
crosses  the  upper  vertical  meridian  at  55°,  the  median  meridian  at 
<;0°,  the  lower  vertical  meridian  at  70°,  and  the  external  meridian 
beyond  !)0°.     The  field  for  yellow  light  is  witliin  that  for  white,  the 


Fig.    371. — Diagram    of   Right   Homonymous   Hemianopsia    and    of    the 
sites  of  lesions  which  may  cause  it.      (  Ball.  ) 

RE,  Right  eye.  LE,  Left  eye.  ON,  Optic  nerve.  C,  Chiasma.  OT,  Optic 
tract.  Th,  Thalaml  optici.  O,  Corpora  geniculata.  Q,  Corpora  quadrigemina. 
RC,  Right  cuneus.     OR,  Optic  radiations. 


field  for  blue  light  within  that  for  yellow,  the  field  for  red  within 
that  for  yellow,  and  the  field  for  green  is  much  smaller. 

Pathological. — Argyll-Eobertsox  Pupil. — Here  there  is  no 
contraction  of  the  pupil  to  light  (no  light-reflex) ;  but  it  does  con- 
tract when  the  accommodation  is  called  into  play  for  near  objects,. 


VISION.  747 

it  has  accommodation-reflex.  It  occurs  in  locomotor  ataxia  and  in 
paresis.  Both  pupils  act,  though  only  one  retina  is  stimulated,  owing 
to  the  intercentral  coupling  of  the  two  constricting  centers  of  the 
pupil.  In  dyspnoea  the  pupil  dilates,  but  wheh  asphyxia  ensues  the 
dilatation  diminishes.  Atropine  paralyzes  the  oculomotorius  terminals 
(thus  paralyzing  accommodation),  but  after  its  section  the  dilatation 
of  the  pupil  is  still  further  increased  by  atropine;  hence  it  must  be 
an  action  on  the  dilating  fibers.  Eserin,  a  myotic,  contracts  the 
pupil,  due  to  stimulation  of  the  oculomotor.  The  ansesthetics  con- 
tract the  pupil,  but  when  their  action  is  deep  they  dilate  it. 

Weenicke's  Hemiopia  Pupillaky  Eeaction. — If  the  light  is 
thrown  on  the  hemianopic  half  of  the  retina,  the  pupil  remains  inac- 
tive. Here  there  is  an  interruption  in  the  path  between  the  retina 
and  the  geniculate  bodies;  the  hemiopia  is  not  central,  but  due  to 
a  lesion  in  the  tract  of  the  optic  nerve.  If  the  light  is  thrown  on 
the  sensitive  half  of  the  retina,  the  pupil  immediately  contracts. 


CHAPTER  XX. 

CRANIAL    NERVES. 

The  cranial  nerves  are  twelve  pairs  of  nerves  which  reach  their 
respective  terminations  after  passage  through  foramina  located  in 
the  base  of  the  cranium.  They  are  designated  numerically,  begin- 
ning from  the  anterior  jDortion  of  the  base  of  the  brain  backward,  as 
well  as  by  names  dependent  upon  their  functions  and  distribution. 
They  are  as  follows: — 

1.  Olfactory.  5.  Trifacial.  9.  Glosso-pharyngeal. 

2.  Optic.  G.  Abducent.  10.  Pneuniogastric. 

3.  !Motor  oculi.  7.  Facial.  11.  Spinal  accessory. 

4.  Pathetic.  8.  Auditory.  12.  Hypoglossal. 

Origin  of  the  Cranial  Nerves. — Upon  examination,  each  cranial 
nerve  is  found  to  possess  a  point  of  superficial  orifjin  as  well  as  a 
nucleus  of  deep  origin. 

The  superficial  origin  is  that  point  upon  the  brain's  surface 
where  each  nerve  emerges.  This  is  but  the  apparent  origin  of  each 
pair  of  nerves,  since  their  individual  fibers  may  be  traced  more 
deeply. 

Each  cranial  nerve  has  a  special  nucleus  of  gray  matter  lying 
deeply  within  the  brain-substance.  The  nucleus  consists  of  a  col- 
lection of  cells  from  whose  prolongations  spring  the  axis-cylinders 
which  constitute  the  fibers  of  the  nerves. 

The  gray  masses  which  represent  the  prolongations  of  the 
anterior  horns  of  the  cord  into  the  medulla  oblongata  form  the 
nuclei  of  origin  of  the  cranial  motor  nerves.  The  base,  separated 
from  the  head  of  the  horn  by  decussation  of  the  pyramidal  columns, 
remains  contiguous  to  the  central  canal.  It  is  prolonged  in  its 
entirety  upon  the  floor  of  the  fourth  ventricle,  lying  upon  each  side 
of  the  raphe.  Beneath  the  trigonum  hypoglossi  lies  the  nucleus  of 
tlie  hypoglossal;  beneath  the  eminentia  teres  is  found  the  common 
nucleus  of  the  facial  and  abducent;  the  nuclei  of  the  oculomotor  and 
pathetic  lie  upon  each  side  of  the  aqueduct. 

Tlxe  head  of  the  anterior  horn,  cut  into  fragments  by  the  motor 
decussation,  forms  that  which  is  known  as  the  antero-lateral  nucleus. 
This  is  the  motor  nucleus  of  the  mixed  nerves.  Bv  its  most  internal 
(748) 


CRANIAL  NERVES.  749 

parts  it  represents  the  accessory  or  anterior  nucleus  of  the  hypo- 
glossus;  farther  up,  tlie  proper  nucleus  of  the  facial;  and  in  the 
pons  there  is  found  the  motor  root  of  the  trigeminus. 

The  gray  masses  of  the  posterior  horns  of  the  cOrd,  prolonged 
into  the  medulla  oblongata  and  cut  by  the  sensory  decussation  or 
fillet,  form  the  sensiiire  nuclei  of  the  cranial  nerves.  The  base  of 
the  posterior  horn  forms  the  sensory  nucleus  of  the  mixed  nerves, 
namely :  glosso-pharyngeal,  vagus,  and  spinal  accessory.  Above 
these  nuclei  there  is  a  gray  layer  which  represents  the  oblongata  cen- 
ter of  the  internal  root  of  the  auditory;  higher  still  arises  the  sen- 
sory nucleus  of  the  trigeminus.  The  head  of  this  horn,  under  the 
name  of  gray  nucleus  of  Kolando,  ascends  in  the  pons  to  form  the 
ascending  root  of  the  trigeminus. 

Among  the  twelve  pairs  of  cranial  nerves,  ten  have  their  points 
of  origin  in  cells  of  the  gray  nuitter  of  the  cord.  This  latter  has 
been  prolonged  into  the  medulla  oblongata  and  pons  in  the  form  of 
four  motor  and  sensory  columns.  Thus  these  cranial  nerves  are  com- 
parable to  spinal  nerves. 

Comparable  to  Spixal  Xerves. — The  law  of  double  root  is  as 
applicable  here  as  to  the  spinal  nerves.  Those  nerves  destined  for 
movement  originate  in  the  prolongations  of  the  anterior  horns,  while 
those  which  preside  over  sensibility  take  their  origin  in  gray  matter 
of  the  medulla  and  pons  which  has  sprung  from  the  posterior  horns 
of  the  spinal  cord. 

Point  of  Difference. — There  is  this  difference,  however,  between 
cranial  and  spinal  nerves:  In  the  spinal  nerves,  the  two  roots  are 
intimately  united  just  outside  of  the  spinal-cord  substance  to  form 
a  mixed  nerve.  In  the  case  of  the  cranial  nerves  the  posterior  sen- 
sory roots  and  the  anterior  motor  roots  remain,  for  the  most  part, 
separated  to  form  nerves  that  are  either  exclusively  motor  or  exclu- 
sively sensory.  In  other  words,  the  cranial  nerves  represent  the  dis- 
sociated spinal  nerves  in  which  the  anterior  and  posterior  roots 
remain  habitually  isolated  to  form  nerves  which  are  either  fine  con- 
ductors of  motion  or  sensation,  dependent  upon  their  source. 

In  the  hypoglossal  alone  are  fulfilled  the  true  characteristics, 
for  in  numerous  cases  it  is  fouiid  to  have  a  ganglion  upon  its  pos- 
terior root. 

The  mesencephalon  has  been  considered  to  possess  parallel  fea- 
tures with  the  spinal  cord,  in  that  it  is  formed  of  a  series  of  seg- 
ments corresponding  to  the  cranial  nerves.  As  the  student  already 
knows,  each  spinal  nucleus  has  peripheral  conductors  which  bring  to 


750 


PHYSIOLOGY. 


the  cord  its  sensory  impressions,  and  motor  nerves  to  conduct  to  the 
muscles  the  motor  reactions.  In  the  same  way  the  central  conduc- 
tors of  the  brain  bring  to  it  sensory  impressions  and  by  its  motor 
fibers  carry  out  motion.  Hence  it  results  that  all  of  the  sensory 
fibers  of  centripetal  course  have  their  origin,  not  in  the  gray  nuclei 
of  the  medulla  oblongata,  but  in  the  ganglia  annexed  to  the  dorsal 
roots  of  the  cranial  nerves. 

The  oblongata  nuclei  are  but  terminal  nuclei,  for  in  them  the 
sensory  fibers  terminate  by  fine  arborizations-  w^hich  surround  the 
central  cells  without  penetrating  them.  The  termination  is  identical 
wdth  that  of  the  sensory  roots  Qf  the  spinal  nerve. 


JX,  IS.  w. 


Fig.  372. — Position  of  the  Xuclei  of  the  Cranial  Nerves. 
(After  Edinger.) 

The  medulla  oblongata  and  pons  are  Imagined  as  transparent.     The  nuclei 
of  origin  (motor),  black;    the  end  nuclei  (sensory),  red. 

The  sensory  fibers  of  the  tenth,  ninth,  seventh,  and  fifth  pairs 
of  cranial  nerves,  as  well  as  that  of  the  auditory,  originate  in  their 
respective  ganglia.  Thus,  there  is  the  jugular  for  the  tenth  pair, 
the  jugular  and  petrosal  for  the  ninth  pair,  the  geniculate  for  the 
seventh,  Gasserian  for  the  fifth,  and  Scarpa's  and  spiral  ganglia  for 
the  eighth  pair. 

On  the  contrary,  the  motor  fibers  of  the  cranial  nerves  arise  in 
the  central  cells  of  the  medulla  and  pons,  just  like  the  motor  fibefs 
of  the  spinal  cord.  Thus,  fine  anatomy  demonstrates  that  the 
cranial,  like  the  spinal,  nerves  have  dovhie  roofs. 

Decussations. — The  afferent  or  sensory  cranial  nerves  do  not 
decussate.     Of  the  motor  cranial  nerves,  the  third  and  fourth,  the 


CRANIAL  NERVES.  751 

motor  root  of  the  fifth,  the  seventh,  the  motor  root  of  the  vagus, 
the  giosso-pharyngeal,  and  the  hypoglossal  decussate  partially.  The 
jjathetic  decussates  completely  in  the  valve  of  Vieussens.  The  last- 
named  nerve  springs  from  the  oculomotor  nucleus  united  with  that 
of  the  pathetic.  These  portions  of  gray  matter  are  a  direct  part 
of  the  anterior  horn  of  the  spinal  cord  lying  heneath  the  aqueduct 
of  Sylvius. 

In  Chapters  XYII  and  XIX  were  considered  the  olfactory,  or 
first  pair  of  cranial  nerves,  and  the  optic,  or  second  pair;  so  that  in 
this  chapter  there  will  be  taken  up,  first,  the  motor  oculi,  or  third 
pair  of  cranial  nerves. 

THIRD  PAIR,   OR  MOTOR  OCULI   NERVE. 

This  nerve  arises  from  a  nucleus  situated  between  the  corpora 
ciuadrigemina  and  beneath  the  floor  of  the  aqueduct  of  Sylvius. 
Beneath  the  posterior  end  of  the  anterior  corpus  quadrigeminum 
this  nucleus  becomes  continuous  with  the  nucleus  of  the  trochlearis 
or  patheticus.  The  oculomotor  nuclei  consist  (1)  of  a  group  of 
cells  concerned  in  accommodation;  (2)  those  concerned  in  the  reflex 
action  of  the  iris  to  light;  (3)  the  innervation  of  all  the  muscles  of 
the  eye  except  the  external  rectus  and  superior  oblique.  The 
neuraxons  of  these  cells  pass  by  and  through  the  red  nucleus  and 
emerge  at  the  inner  side  of  the  cerebral  crura,  to  pass  through  the 
interpeduncular  space  along  the  outer  boundary  of  the  cavernous 
sinus;  they  then  enter  the  sphenoidal  fissure,  and  go  to  the  muscles 
of  the  eyeball,  except  the  external  rectus  and  superior  oblique.  It 
also  gives  fibers  to  the  ciliary  muscle  and  the  sphincter  of  the  pupil 
and  a  branch  to  the  elevators  of  the  upper  lid. 

The  posterior  longitudinal  bundle  is  also  connected  with  the 
nuclei  of  the  third,  fourth,  and  sixth  nerves.  The  oculomotor 
nucleus  also  has  a  connection  with  the  optic  neurons  in  the  anterior 
corpora  quadrigemina.  In  the  cavernous  sinus  it  receives  filaments 
coming  from  the  carotid  branches  of  the  great  sympathetic  and  a 
branch  from  the  ophthalmic  of  the  trigeminus. 

Functions.- — From  a  functional  point  of  view,  it  may  be  said  that 
tlie  motor  oculi  is  devoted  exclusively,  in  conjunction  with  the  fourth 
and  sixth  pairs  of  nerves,  to  making  the  sight  perfect.  With  these 
nerves  it  concurs  to  regulate  the  varied  movements  which  allow  the 
eye  to  act  as  a  telescope  upon  a  support  that  is  furnished  •«dth 
numerous  articulations.  By  means  of  these  muscles  and  nerves  of 
the  orbit  the  individual  is  enabled  to  remove  the  visual  field  from 


752 


I'liyyiOLOGY. 


place  to  iDlacG  and  in  all  directions  to  any  objects  which  he  might 
wish  to  examine. 

For  its  part,  the  motor  ocnli  allows  the  eye  to  see  particularly 
objects  that  are  situated  high  or  low  or  at  one  side.  However,  it 
has  a  most  important  function  in  the  harmony  of  the  associated 
movements  by  which  two  images  fall  upon  identical  points  of  the 
retina  of  the  two  eyes,  thus  causing  but  one  and  the  same  impression. 

The  third  pair  of  nerves  manages  to  regulate  the  amount  of 
light  which  falls  upon  the  retina?.  Its  function  in  this  capacity  is 
to  protect  the  optic  nerve  against  a  too  intense  excitement  from 


Fig.  373. — Distribution  of  the  Third  and  Sixth  Nerves  in  the  Orbit. 

(  Lf:VEILLE. ) 

1,  The  third  nerve.  2,  Its  superior  division.  3,  Its  inferior  division.  4, 
Branch  to  the  inferior  oblique  muscle.  !J,  The  sixth  nerve  distributed  to  the 
external  rectus  muscle. 

excessive  light.  By  contracting  the  pupil  it  lessens  the  pencil  of 
light  which  penetrates  into  the  depths  of  the  ocular  globe. 

On  the  contrary,  it  is  the  sympathetic  which  produces  dilatation 
of  the  pupil  so  that  the  retina  may  receive  all  of  the  light  which  can 
be  reflected  from  obscure  objects.  For  the  accomplishment  of  con- 
traction and  dilatation  of  the  pupil  it  must  be  remembered  that  the 
iris  comprises  two  kinds  of  muscular  fibers:  circular  and  radiating. 
The  former  are  connected  with  the  motor  oculi;  the  latter  with  the 
sympathetic. 

Finally,  the  third  nerve  is  considered  to  have  an  important 
function  in  the  act  of  accommodation. 


CEANIAL  NERVES.  753 

Pathology. — The  motor  oculi  is  frequently  a  sufferer  by  reason 
of  its  situation  and  course.  It  is  often  compressed  by  tumors  at 
the  base  of  the  brain.  In  its  passage  through  the  sinus  cavernosus 
it  is  exposed  to  compression  by  a  thrombosis  of  this  venous  canal. 

The  course  of  the  third  nerve  through  the  interpeduncular  space 
makes  it  play  a  considerable  part  in  pathology.  This  is  the  place  of 
predilection  for  meningitic  deposits.  This  segment  of  the  nerve  is 
most  frequently  compressed  in  the  exudates  of  tubercular  meningitis. 
It  is  also  the  point  of  attack  of  constitutional  syphilis,  particularly 
during  the  tertiary  period;  this  is  a  chronic  meningitis  which  has 
its  principal  focus  at  the  interpeduncular  space  as  an  exudate.  Diph- 
theritic infection  often  attacks  the  third  pair  of  cranial  nerves. 

Paralysis  of  the  oculomotor  gives  rise  to  external  squint.  Its 
irritation  causes  internal  squint,  and  also  contraction  of  the  pupil, 
or  myosis.  The  eye  deviates  outward  in  paralysis,  due  to  the  action  of 
the  external  rectus  not  being  antagonized  by  the  internal  rectus. 

Diplopia. — The  deviation  of  one  of  the  eyes  does  not  permit  the 
maintenance  of  parallelism  of  the  visual  axes.  Without  this  coinci- 
dence the  two  images  will  not  fall  upon  identical  points  in  the  retina. 
Hence  all  objects  seen  will  be  double.  This  symptom,  known  as 
diplopia,  renders  the  sight  very  uncertain  and  often  produces  vertigo. 

Should  the  paralysis  be  general,  so  that  it  comprises  the  elevator 
of  the  lid,  jSTature  brings  for  itself  a  remedy  for  the  defect  of  diplopia 
by  suppressing  the  vision  of  one  eye.  It  does  this  by  letting  the  lid 
fall  over  the  deviating  eye.  This  drooping  of  the  lid  gives  the  con- 
dition known  as  ptosis. 

Stimulation  of  the  motor  fibers  of  the  third  can  be  produced 
reflexly  by  teething  or  intestinal  irritations  of  children;  hence  their 
squint.  Chronic  spasms  of  the  eye-muscles  which  are  involuntary 
are  called  by  the  name  nystagmus. 

Drugs. — Atropine  paralyzes  the  intra-ocular  ends  of  the  motor 
oculi;    Calahar  bean  stimulates  them  or  paralyzes  the  sympathetic. 

FOURTH  PAIR,  OR  PATHETIC  NERVE. 

Distribution. — The  pathetic  supplies  the  superior  oblique  muscle. 

Physiology. — If  the  peripheral  end  of  the  pathetic  be  electrically 
irritated,  the  superior  oblique  muscle  contracts  and  turns  the  eyeball 
downward  and  outward. 

The  pathetic  is  a  nerve  that  is  especially  endowed  for  the  realiza- 
tion of  simple  vision  with  the  two  eyes  in  inclined  positions  of  the 
head.     It  is  impossible  for  an  individual  to  carry  one  eye  downward 

48 


-54 


PHYSIOLOGY. 


and  outward.  That  is,  he  cannot  make  a  movement  directed  l)y  the 
superior  oblique  and  still  keep  the  Iread  perfectly  vertical.  It 
becomes  necessary  that  the  head  be  inclined  to  one  side,  and  at  the 
time  this  inclination  is  produced  the  rotation  of  the  eyeball  occurs 
without  the  will  having  the  power  to  prevent  it.  By  the  very  act 
of  inclination  of  the  head  the  necessary  parallelism  of  the  two  eyes 
is  positively  destroyed;  hence  this  involuntary  action  of  the  supe- 
rior oblique  to  place  the  visual  axes  upon  the  same  plane. 


Nucleus  of  oculo-motor, 

'  Edinger-Westphal  nucleus. 
Principal  nucleus. 
Median  nucleus. 


Nucleus  of  fourth  nerve. 


Fig.  374. — Nuclei  of  Origin  of  the  Third  and  Fourtli  Nerves, 
(PoiRiER  and  Charpy.) 

The  fourth  pair  of  cranial  nerves  arise  from  a  collection  of  cells 
beneath  the  anterior  part  of  the  posterior  corpus  quadrigeminum. 
It  completely  decussates  in  the  superior  medullary  velum.  It  starts 
behind  the  quadrigeminal  body  and  then  appears  like  a  white  thread 
winding  around  the  outer  side  of  the  crus  of  the  cerebrum.  It  then 
pierces  the  dura  mater,  runs  along  the  outer  wall  of  the  cavernous 
sinus,  and  enters  the  sphenoidal  foramen  with  the  oculomotor  and 
abducent.     It  supplies  the  superior  oblique  muscle  of  the  eye. 

Pathology. — Usually  the  first  sign  of  any  disorder  of  the  pathetic 
is  a  giddiness  when  ascending  or  descending  a  stairs,  owing  to  the 


CRANIAL  NERVES.  755 

double  vision  that  occurs  when  the  patient,  in  going  down,  looks 
at  his  steps. 

To  overcome  this  diplopia  he  gives  to  his  head  a  position  that 
is  quite  characteristic.  He  holds  his  head  bent  forward  and  directed 
to  the  ground.  This  position  overcomes  the  necessity  of  moving  the 
eyeballs  from  above  downward  aud  so  minimizes  the  liability  to 
diplopia. 

SIXTH  PAIR,  OR  ABDUCENT  NERVE. 

This  nerve  arises  from  a  collection  of  ceils  seated  beneath  the 
floor  of  the  fourth  ventricle  below  the  stria  acustica^.  The  loop  of 
the  facial  incloses  it.  The  abducent  emerges  between  the  summits 
of  the  pyramidal  bodies  of  the  medulla  oblongata  and  the  pons.  As 
a  threadlike  nerve  it  goes  through  the  cavernous  sinus  and  through 
the  sphenoidal  foramen  to  the  external  rectus.  The  nucleus  of  the 
abducent  has  a  connection  with  the  posterior  longitudinal  bundle  of 
fibers  to  the  opposite  oculomotor  nucleus,  thus  permitting  associated 
movements  of  the  eyeball.  The  pontal  olives  are  connected  by  fibers 
with  the  oculomotor  nucleus.  And  these  olives  are  also  connected 
with  the  auditory  nuclei  and  these  nuclei  are  connected  with  the 
cerebellum,  so  that  there  is  an  association  between  the  motor  nerves 
of  the  eye,  the  auditory  nerves,  and  the  cerebellum. 

Physiology. — The  sixth  nerve  is  exclusively  motor.  It  has  for 
its  only  aim  to  excite  the  external  rectus.  When  the  nerve  is 
strongly  galvanized  the  eyeball  deviates  outward.  Its  section,  on 
the  contrary,  produces  an  internal  strabismus.  It  is  especially 
adapted  for  seeing  objects  placed  to  one  side.  In  general,  the 
abducent  is  but  one  of  the  elements  for  the  exercise  of  perfect 
vision. 

Pathology. — Paralysis  is  the  most  common  manifestation  in  the 
sixth  pair.  A  considerable  concussion  of  the  orbital  cavity,  espe- 
cially when  it  is  upon  the  external  side,  will  particularly  paralyze 
the  ab'ducent.  Unilateral  paralyses  of  this  nerve  are  usually  of  peri- 
pheral origin.  Bilateral  paralysis  is  generally  due  to  central  dis- 
turbance. The  most  prominent  symptom  of  this  affection  is  an 
internal  or  convergent  strabismus.  The  eye  is  held  inward  by  the 
tonus  of  the  rectus  intcrnus,  so  that  not  more  than  one  part  of 
the  cornea  is  perceived. 


756  PHYSIOLOGY. 

CONJUGATE  DEVIATION. 

Waller  explains  this  as  follows:  The  two  eyes  arc  exactly  equal 
and  parallel  for  different  directions  of  distant  vision.  Both  eyes  are 
turned  to  the  right  or  to  the  left,  up  or  down,  so  that  the  object 
lixed  gives  images  on  corresj^onding  parts  of  both  retina?.  In  move- 
ments directly  u])ward  or  downward  muscles  of  the  same  name  in 
each  eye  are  associated  in  action;  but  in  lateral  movements  the  asso- 
ciation is  asymmetrical :  e.g.,  the  external  rectus  of  one  eye  acts  with 
the  internal  rectus  of  the  other,  and  the  peculiarity  of  this  asso- 
ciated action  seems  still  more  striking  when  it  is  remembered  that 
the  external  rectus  is  supplied  by  the  sixth  nerve,  while  the  internal 
rectus  is  supplied  by  the  third.  A  similar,  if  less  striking,  associa- 
tion of  asymmetrical  muscles  on  the  two  sides  occurs  in  the  rotation 
of  the  head  and  nock,  which  arc  turned  to  the  right  by  the  right 
inferior  oblique  and  the  left  sterno-mastoid  muscles,  and  to  the  left 
by  the  left  inferior  oblique  and  the  right  sterno-mastoid.  In  look- 
ing to  the  right  we  contract  the  right  external  and  left  internal 
recti:  i.e.,  impulses  pass  through  the  right  sixth  nerve  and  the  left 
third,  possibly  from  the  left  and  from  the  right  side,  respectively,  of 
the  motor  cortex,  but  more  probal)ly  from  only  the  left  motor  cor- 
tex, in.  which  case  we  must  suppose  that  certain  nerve-fibers  cross 
twice:  once  between  the  cortex  and  bulljar  nucleus  and  a  second 
time  between  the  nucleus  and  nerve-termination.  Unilateral  con- 
vulsions of  cortical  origin  are  accompanied  by  rotation  of  the  head 
and  eyes  toward  the  convulsed  side:  i.e.,  away  from  the  cerebral 
lesion.  Thus  a  discharging  lesion  of  the  right  motor  cortex  causes 
convulsions  of  the  left  side  of  the  body,  with  rotation  of  the  eyes 
to  the  left.  This  is  a  "conjugate  deviation."  A  destructive  lesion 
of  the  right  motor  cortex  causes  paralysis  of  the  left  side  of  the 
bod}^  with  rotation  of  the  eyes  to  the  right.  The  peculiarity  in  this 
case  is  that  there  is  a  cessation  of  action  along  the  left  sixth  nerve 
(external  rectus)  and  the  right  third  nerve  (internal  rectus),  the 
deviation  of  the  eyes  to  the  right  being  caused  by  the  unbalanced 
action  of  the  muscles,  which  rotate  the  eyes  to  the  right. 

FIFTH  PAIR,  TRIGEMINUS,   OR  TRIFACIAL   NERVE. 

The  fifth  pair  of  nerves,  like  a  spinal  nerve,  has  two  roots:  an 
anterior  motor  one  and  a  posterior  sensory  one.  The  neuraxons  of 
the  motor  nucleus  in  the  pons  make  up  the  motor  root.  The  sen- 
sory arises   in   the    Gasserian  ganglion,   and,  like   a   posterior-root 


CRANIAL  NERVES. 


757 


Fig.  375. — Tlie  Origin  of  the  Trigeminal  Nerve, 


758  PHYSIOLOGY. 

ganglion,  its  neuraxons  are  divided,  one  j^art  going  to  the  skin  of 
the  face  and  the  other,  running  toward  the  pons,  also  divides  into 
two  parts,  one  going  upward  and  the  other  downward.  The  gela- 
tinous substance  of  Kolando  on  the  posterior  horn  receives  the  fibers 
running  downward,  which  arborize  around  the  cells. 

The  descending  part  of  the  trigeminus,  known  as  the  ascending 
root,  extends  down  to  the  second  cervical  vertebra,  continually  giv- 
ing off  collaterals  as  it  descends,  which  arborize  around  the  gelatin- 
ous substance  of  Eolando  of  the  posterior  horn,  thus  making  the 
lower  trigeminal  nucleus  a  long  one.     The  descending  branch  also 


Fig.  37G. — Oplithalmie  Division  of  the  Fifth  Nerve.     (LE^iiiiLL^.) 

1,  Skin  of  the  forehead  turned  down.  2,  Optic  nerve.  3,  Third  nerve.  4, 
Fourth  nerve.  5,  Ophthalmic  division  of  the  fifth  nerve.  6,  Lacrymal  branch. 
7,  Union  of  the  fourth  nerve  with  the  lacrymal  branch  of  the  fifth.  8,  Frontal. 
9,  Nasal.     10,  Internal  branch  of  nasal. 

has  collaterals,  which  arborize  around  the  motor  nuclei  of  the  hypo- 
glossal, facial,  and  trifacial.  The  neuraxons  of  the  sensory  nuclei 
in  which  the  trigeminus  ends  decussate  and  go  to  the  cortex  in  the 
fillet. 

Cortical  Connection. — The  sensory  path  ends  in  the  inferior  part 
of  the  central  region  of  the  cortex,  going  up  in  the  fillet  and  the 
thalamus.  The  nucleus  of  the  motor  root  lies  in  the  pons,  near  the 
sensory  nucleus  of  the  trigeminus  and  back  of  the  nucleus  of  the 
facial,  of  which  it  is  probably  a  part.  There  is  another  nucleus,  the 
accessory  nucleus  of  the  motor  nucleus,  which  is  situated  beneath 
the  aqueduct  of  Sylvius,  and  which  sends  descending  fibers  to  the 
motor  nucleus. 


CRANIAL  NERVES.  759 

The  trigeminus  emerges  from  the  pons  by  two  roots:  a  large 
sensory  root  and  a  small  motor  root.  The  large  root  has  the  Gas- 
serian,  or  semilunar,  ganglion,  while  the  small  root  runs  beneath  it. 
From  the  semilunar  ganglion  emanate  the  ophthalmic,  superior  max- 
illary, and  a  third  branch,  which  joins  the  small  root  of  the  trifacial 
to  form  the  inferior  maxillary  nerve.  The  nasal  branch  of  the 
ophthalmic,  ciliary,  or  lenticular  ganglion  gives  off  the  ciliary  nerves 
for  the  ciliary  muscle  and  iris.  This  ganglion  receives  motor  fibers 
from  the  oculomotor  nerve  and  branches  from  the  sympathetic. 
The  superior  maxillary  branch  passes  through  the  rotund  foramen 
of  the  sphenoid  bone  and  gives  off  dental  nerves  and  spheno-palatine 
nerves  which  go  to  Meckel's,  or  the  spheno-palatine,  ganglion.  It 
gives  off  nasal,  palatine,  and  pterygoid  nerves.  The  pterygoid  nerve 
gives  off  a  branch,  the  great  petrosal,  which  enters  the  cranial  cavity 
through  the  cavity  of  the  foramen  lacerum  and  enters  a  canal  on 
the  front  of  the  petrous  portion  of  the  temporal  bone  to  join  the 
facial  nerve.  The  inferior  maxillary  nerve  is  formed  of  the  small 
motor  root  of  the  trigeminus  and  a  third  branch  of  the  semilunar 
ganglion,  and  makes  its  exit  from  the  skull  by  the  oval  foramen.  It 
gives  off  the  auriculo-temporal  and  the  lingual  nerve,  which  in  its 
course  is  joined  by  the  chorda  tympani  of  the  facial  and  the  inferior 
dental  nerves.  On  the  sensory  division  of  the  inferior  maxillary 
nerve  is  seated  the  otic,  or  ganglion  of  Arnold.  From  it  emanates 
the  small  petrosal  nerve,  which  enters  the  cranium  through  a  fine 
canal  in  the  spinous  process  of  the  sphenoid  bone  and  then  courses 
along  a  canal  in  front  of  the  petrous  portion  of  the  temporal  bone 
to  join  the  facial.  The  otic  ganglion  gives  out  filaments  to  the  ten- 
sor palati  and  tensor  tympani  muscles. 

Physiology. — From  the  point  of  view  of  general  sensibility  the 
trigeminus  possesses  a  considerable  domain.  To  it  alone  is  intrusted 
the  giving  of  general  sensibility  to  nearly  all  parts  which  enter  into 
the  composition  of  the  head.  In  the  external  covering  of  the  head 
but  one  region  escapes  it.  This  is  the  lateral  and  posterior  part  of 
the  hairy  scalp,  the  innervation  for  the  latter  coming  from  the  cer- 
vical nerves. 

As  to  mucous-membrane  sensibility,  trifacial  innervation  comes 
only  to  the  posterior  third  of  the  tongue,  where  the  glosso-pharyn- 
geal  innervates  the  palate,  with  the  middle  and  inferior  parts  of  the 
phar}'nx. 

These  points  being  eliminated,  it  gives  tactile  sensibility  not 


7G0 


PHYSIOLOGY. 


only  to  the  skin,  bnt  also  to  all  of  the  tissues  of  the  head,  compris- 
ing the  glands,  meninges,  organs  of  sense,  bone,  and  dental  pulp. 

Reflex  Relations. — By  reason  of  the  ciliary  filaments  the  trigem- 
inus is  in  particular  reflex  relation  with  the  motor  oculi  and  sympa- 


HtLit.  teraporallJ. 


HuBC  masseter 


N.  hypoplospnii. 


riatysma  inyoide^. 
Muse,  sternohyoideua. 

Muse,  steriiothyreoideui 

Muse,  omohyoideufl. 


Kd.  thuracici  anteriores. 


Unsc  splentna. 

Muse,  steriiocleidomaatoideiu. 

I^.  accesaorius 

Muse.  levator  anguli  scapulae 

Muse.  cueull;irw  or  trapeziu*. 
K.  dora&lia  acapulaa. 


N.  axLllArU. 

N.  thoracinu  Ungb. 


H.  pIiTenicus. 


ErVa 
BupraclavlcuJIar* 


Fig.  377. — Distribution  of  the  Sensory  Nerves  of  the  Head,  together  with 
the  Situation  of  the  Motor  Points  on  the  Neck.     (Landois.) 

SO,  Distribution  of  the  supraorbital  nerve.  ST,  Supratrochlear  nerve.  IT, 
Infratrochlear  nerve.  L,  Lacrymal  nerve.  N,  Ethmoid  nerve.  10,  Infraorbital 
nerve.  B,  Buccinator  nerve.  SM,  Subcutaneous  malar  nerve.  AT,  Auriculo- 
temporal nerve.  AM,  Great  auricular  nerve.  OMj,  Greater  occipital  nerve. 
OMi,  Lesser  occipital  nerve.  C3,  Third  cervical  nerve.  CS,  Cutaneous  branches 
of  the  cervical  nerves.  CW,  Situation  of  the  central  convolutions  of  the  cere- 
bral hemisphere.     8C,  Situation  of  the  speech-center  (third  frontal  convolution). 

thetic.  Because  of  the  ramifications  of  the  trifacial  branches  in  the 
mucous  membrane  of  the  nose  there  is  established  a  very  intimate 
relation  with  the  expiratory  muscles  and  nerves.  Even  the  slightest 
touch  may  occasion  a  sudden  and  violent  sneeze.     A  close  relation- 


CRANIAL  NERVES.  761 

ship  exists  betAveen  this  nerve  and  the  mnscles  and  nerves  of  degluti- 
tion. 

A  remarkable  fact  in  connection  with  the  trigeminus  is  its  great 
functional  resistance  to  various  poisons  which  are  capable  of  paralyz- 
ing nerves  of  sensation.  While  all  other  regions  of  the  body  show 
the  effects  of  anEesthetics,  those  under  the  dominion  of  the  trigem- 
inus still  preserve  a  high  degree  of  sensibility.  Even  though  a 
patient  be  anaesthetized  with  chloroform,  yet  will  he  perceive  punc- 
tures in  the  temples  and  frontal  regions.  This  occurs  in  spite  of 
the  fact  that  sensations  are  not  perceived  elsewhere. 

Motor  Functions. — By  its  short  root  the  trigeminus  holds  under 
its  power  the  movements  of  elevation,  depression,  and  rotation  of 
the  lower  jaw.  If  this  root  be  cut,  it  is  found  that  the  muscles  con- 
cerned in  the  performance  of  the  above-mentioned  movements  are 
paralyzed.  The  lower  jaw  remains  passively  separated  from  the 
upper. 

Trophic  Function. — AVithin  twenty-four  hours  after  intracranial 
section  of  the  trigeminus,  the  cornea  becomes  opaque.  At  the  end 
of  five  or  six  days  the  cornea  becomes  ver}^  white  in  color.  The  iris 
becomes  inflamed  and  covered  with  false  membranes.  In  about  eight 
days  the  cornea  becomes  detached  and  the  contents  of  the  eye  escape. 

The  suppression  of  the  fifth  pair  is  followed  by  remarkable 
alterations  in  the  Schneiderian  membrane.  It  becomes  spongy,  and 
bleeds  upon  the  least  touch.  The  place  where  the  olfactory  bulbs 
lie  is  completely  changed.  Thus  the  acts  of  olfaction  and  vision  are 
indirectly  affected. 

Pathology. — By  reason  of  the  intimate  association  of  the  trigem- 
inus, and  its  Gasserian  ganglion,  with  the  petrous  portion  of  the 
temporal  bone,  it  is  exposed  to  all  of  the  shocks  and  blows  that  are 
able  to  fracture  this  bone. 

The  relations  of  the  trigeminus  with  its  meninges  are  very  apt 
to  be  disturbed  seriously  by  the  presence  of  tumors.  The  false  mem- 
branes which  are  found  in  meningitis  compress  it  and  so  produce 
atrophy.  The  exudates  of  tubercular  meningitis  very  often  produce 
anaesthesia  of  the  face. 

The  fifth  pair  is  mout  often  the  seat  of  either  excessive  sensi- 
bility or  paralysis.  It  is,  perhaps,  the  one  nerve  which  is  the  most 
frequently  affected  in  neuralgia.  The  relative  nearness  of  the  tri- 
geminus to  its  sensory  center  probably  explains  the  acuteness  of  tlie 
pains  in  neuralgia. 


702  PHYSIOLOGY. 

SEVENTH  PAIR,  FACIAL  NERVE,  OR  PORTIO  DURA. 

The  facial  nerve  arises  from  a  nucleus  beneath  the  floor  of  the 
fourth  ventricle.  This  nerve  contains  a  motor  and  a  sensory  root. 
The  sensory  root  comes  from  the  cells  of  the  geniculate  ganglion,  and 
is  called  the  nerve  of  Wrisberg.  The  motor  pontal  nucleus  gives  oft' 
the  neuraxons  of  the  motor  root.  The  motor  nucleus  is  thought  to 
be  the  upward  part  of  the  nucleus  ambiguuS;,  which  originates  the 
motor  fibers  in  the  vagus  and  glosso-pharyngeal  nerves.  The  neu- 
raxons of  the  motor  nucleus  form  a  distinct  knee,  which  uprising  on 
the  floor  of  the  fourth  ventricle  is  known  as  the  eminentia  teres. 
The  facial  nerve  in  its  course  to  the  periphery  makes  a  peculiar  loop, 
or  knee,  inclosing  the  nucleus  of  the  abducent,  and  emerges  from  a 
depression  back  of  the  pons  between  the  olivary  and  restiform  bodies, 
enters  the  internal  auditory  meatus  with  the  auditory  nerve,  leaves 
the  auditory  nerve,  enters  the  Fallopian  canal,  and  makes  its  exit 
by  the  stylomastoid  foramen  to  go  to  the  muscles  of  the  face.  The 
nerve  of  Wrisl)erg,  or  tlie  sensory  part  of  the  facial,  is  made  up  of 
neuraxons  from  the  cells  of  the  geniculate  ganglion  seated  in  the 
Fallopian  canal.  The  auditory  nerve  is  also  called  portio  mollis,  and 
it  lies  to  the  outer  side  of  the  facial, — the  portio  dura, — and  between 
the  two  is  the  pars  intermedia  portio  inter  duram  et  mollem  of  Wris- 
berg, which  extends  from  the  medulla  to  join  the  facial  in  the 
internal  auditory  meatus.  It  is  connected  with  both  auditory  and 
facial  nerves,  between  which  it  lies.  The  central  neuraxons  of  the 
geniculate  ganglion  or  the  nerve  of  Wrisberg  go  to  the  fasciculus 
solitarius  or  the  vagus  and  glosso-pharyngeal  roots.  The  peripheral 
neuraxons  of  the  geniculate  ganglion  join  the  facial,  and  Duval  states 
that  they  go  to  form  the  nerve  of  taste :  the  chorda  tympani. 

In  the  hiatus  Fallopii  the  great  petrosal  nerve  branches  off  from 
the  facial.  It,  in  conjunction  with  a  filament  from  the  glosso-pharyn- 
geal and  another  from  the  sympathetic,  passes  over  to  join  the  gan- 
glion of  Meckel. 

The  S7naU  petrosal  leaves  the  aqueduct  by  a  particular  opening 
to  end  in  the  otic  ganglion. 

Cortical  Connection. — Tlie  motor  path  from  the  cortex  to  the 
facial  nucleus  arises  from  the  inferior  part  of  the  central  con- 
volutions. 

Chorda  Tympani. — A  few  millimeters  above  the  stylo-mastoid 
foramen  the  facial  gives  off  a  branch  of  very  considerable  size:  the 
chorda  tympani.     It  ascends  into  the  cavity  of  the  tympanum.     It 


CRANIAL  NERVES.  763 

passes  between  the  malleus  and  incus,  giving  a  branch  to  the  lat- 
ter, and  then  enters  the  zygomatic  fossa.  The  chorda  tympani  then 
descends  between  the  two  pterygoid  muscles  to  meet  the  nerve  of 
.taste.  After  communicating  with  the  latter  it  accompanies  it  to  the 
submaxillary  gland.  There  it  joins  the  submaxillary  ganglion  to 
terminate  in  the  lingual  nerve. 

Physiology. — While  the  trigeminus  is  responsible  for  the  sen- 
sibility of  the  face,  the  facial  presides  over  the  contraction  of  the 
facial  muscles  of  expression. 

The  facial  nerve  is  purely  motor,  and  so  has  nothing  to  do  with 
the  transmission  of  sensory  impressions  developed  upon  the  face. 
After  its  section  the  skin  still  preserves  all  of  its  sensibility.  On 
the  other  hand,  after  section  of  the  trifacial  it  completely  disap- 
pears. Though  the  facial  does  not  transmit  sensory  impressions,  yet 
in  itself  it  is  sensitive  because  of  the  branches  which  it  receives  from 
the  trigeminus.  If  the  nerve  be  pinched,  the  animal  shows  signs 
of  pain. 

Pathology. — The  facial  is  the  motor  nerve  which  suffers  most 
easily  from  the  influence  of  cold.  Facial  paralysis,  or  Bell's  palsy, 
may  occur  very  easily  when  draughts  from  a  window  blow  upon  the 
face. 

When  the  paralysis  is  unilateral,  the  face  is  drawn  toward  the 
sound  side.  The  labial  commissure  on  the  paralyzed  side  is  lower 
than  that  on  the  other  side,  thus  giving  to  the  mouth  an  oblique 
direction. 

Bell's  paralysis  is  usually  due  to  a  cold  draught  of  air  striking 
the  nerve  at  its  exit  from  the  stylo-mastoid  foramen.  When  the 
cause  is  seated  in  the  brain  the  external  rectus  is  usually  affected, 
because  its  nerve  is  also  involved  and  usually  there  is  paralysis  of 
the  opposite  half  of  the  body,  or  crossed  paralysis.  Here  the  lesion 
is  in  the  pons.  If  the  lesion  is  seated  in  the  petrous  portion  of  the 
temporal  bone,  there  is  not  only  facial  palsy,  but  also  loss  of  taste 
from  an  involvement  of  the  chorda  tympani. 

EIGHTH   PAIR,  OR  AUDITORY  NERVE. 

The  anatomy  and  function  of  this  nerve  have  been  discussed  in 
Chapter  XVIII.  "^ 

NINTH  PAIR,  OR  QLOSSO=PHARYNGEAL  NERVE. 

The  glosso-pharyngeal  nerve  is  a  nerve  of  both  motion  and  sen- 
sation. 


764  PHYSIOLOGY. 

Cortical  Connections. — Tlio  sensory  ascending  path  of  the  ninth 
nerve  ends  in  the  inferior  part  of  the  central  region  of  the  cortex 
and  in  the  immediate  neighborhood  of  the  posterior  part  of  the  sec- 
ond and  third  frontal  convolutions. 

The  nucleus  ambiguus  gives  off  neuraxons  to  form  its  motor 
root.  The  sensory  neuraxons  arise  'from  the  jugular  and  petrosal 
ganglions  and  arborize  about  two  sensory  nuclei  in  the  medulla 
oblongata.  The  lower  sensory  end  nucleus  produces  an  elevation  on 
the  ficor  of  the  fourth  ventricle,  and  is  called  the  ala-cinerea.  The 
upper  nucleus  is  also  connected  with  sensory  neuraxons  of  glosso- 
pharyngeal nerves,  while  the  lower  portion  of  this  nucleus  is  in  rela- 
tion with  the  vagus.  The  second  nucleus  is  called  the  vertical 
nucleus,  the  fasciculus  solitarius,  the  combined  descending  root  of 
the  pneumogastric  and  glosso-pharyngeal  nerves,  or  the  respiratory 
bundle.  This  respiratory  tract  extends  from  the  olive  down  the 
spine  to  the  eighth  cervical  nerve.  This  respiratory  bundle  of  Gierke 
may  associate  the  nuclei  coordinating  the  various  respiratory  muscles. 
The  glosso-pharyngeal  nerve  arises  by  a  half-dozen  cords  from  the 
restiform  body  and  goes  through  the  jugular  foramen  into  the  vagus, 
where  it  has  a  small  ganglion:  the  jugular.  As  it  emerges  from  the 
jugular  foramen  there  is  developed  the  petrosal  ganglion,  or  gan- 
glion of  Andersch. 

Nerve  of  Jacobson. — This  same  ganglion  gives  origin  to  the  nerve 
of  Jacobson.  It  enters  the  cavity  of  the  tympanum  by  way  of  an 
opening  in  its  floor,  where  it  divides  into  three  filaments.  These  are 
distributed,  one  to  the  round  window,  another  to  the  oval  window, 
and  the  third  to  the  lining  membrane  of  the  Eustachian  tube  and 
tympanum. 

Physiology. — The  ninth  is  a  mixed  nerve.  Its  motor  properties 
are  distributed  to  the  middle  constrictors  of  the  pharynx  and  the 
stylo-pharyngeus  muscle. 

The  most  important  sensory  function  of  the  glosso-pharyngeal 
is  the  part  which  it  plays  in  the  role  of  the  sense  of  taste. 

The  ninth  nerve  has  an  action  upon  the  blood-vessels  of  the 
tongue  that  is  identical  with  that  of  the  chorda  tympani.  If  the 
glosso-pharyngeal  be  cut  and  its  peripheral  end  stimulated,  the 
tongue  becomes  a  livid  red. 

Pathology. — In  man  there  are  no  clear  cases  recorded  where 
there  have  been  uncomplicated  affections  of  the  glosso-pharyngeal. 


CRANIAL  NERVES.  765 

TENTH   PAIR,   PNEUMOGASTRIC,   OR   VAGUS. 

Of  all  of  the  cranial  nerves,  the  vagus  is  the  most  important 
and  has  the  most  functions  of  a  varied  nature  in  clinical  study.  It 
is  a  nerve  of  motion  and  sensation. 

Cortical  Connection. — The  motor  path  to  the  nucleus  of  the 
vagus  is  from  the  inferior  part  of  the  central  convolutions. 

The  motor  neuraxons  arise  from  the  nucleus  ambiguus.  The 
sensory  roots  come  from  the  neuraxons  of  the  jugular  and  petrosal 
ganglions.  The  sensory  neuraxons  have  been  described  under  the 
preceding  nerve:  the  glosso-pharyngeal.  The  vagus  springs  by 
means  of  from  ten  to  fifteen  cords  from  the  groove  behind  the  olivary 
body  and  passes  through  the  jugular  foramen  with  the  glosso-pharyn- 
geal and  spinal  accessor}''  nerves.  In  the  jugular  foramen  it  has  a 
ganglion :  the  jugular  ganglion.  After  it  emerges  from  the  foramen 
it  has  an  enlargement,  the  gangliform  plexus,  or  ganglion  nodosum.    . 

The  plexus  gives  off  the  plianjngcal  and  superior  laryngeal  nerves. 

The  pharyngeal  nerves,  three  in  number,  go  down  the  side  of 
the  pharynx  to  supply  the  mucous  membrane  and  muscles  of  the 
pharynx.  The  superior  laryngeal  goes  down  the  side  of  the  larynx. 
This  nerve  also  furnishes  a  collateral  branch,  important  from  a  phy- 
siological standpoint,  to  the  crico-thyroid  muscle.  It  then  loses 
itself  in  the  mucous  membrane  of  the  larynx. 

At  the  base  of  the  neck  the  vagus  gives  off  another  branch,  the 
recurrent,  or  inferior  laryngeal.  The  nerve  upon  the  right  side 
descends  in  front  of  the  subclavian  artery  and  winds  around  it  pos- 
teriorly from  beneath.  Upon  the  left  side  the  nerve  winds  around 
the  arch  of  the  aorta  in  the  same  manner. 

As  collateral  branches,  the  vagus  furnishes  cardiac  fibers,  which 
form  the  cardiac  plexus  and  are  destined  to  innervate  the  heart. 
There  are  also  oesophageal  fibers  whose  terminations  are  distributed 
to  the  ctsophagus  and  trachea. 

In  the  cervical  region  the  tenth  pair  gives  rise  to  a  branch,  the 
nerviis  depressor.  It  results  by  the  fusion  of  two  fibers:  one  from 
the  superior  laryngeal  and  the  other  from  the  vagus  itself.  The 
nervus  depressor  loses  itself  in  the  cardiac  tissue  of  the  heart  at 
the  level  of  the  aortic  and  pulmonary  orifices. 

During  the  first  portion  of  its  course  the  vagus  forms  numerous 
anastomoses.  These  are  with  the  spinal  accessory,  the  facial,  and 
hypoglossal  cranial  nerves  and  with  a  great  number  of  branches  from 
the  various  ganglia  of  the  sympathetic  system. 


766  PHYSIOLOGY. 

In  the  thorax  the  vagus  gives  off  cardiac  and  pulmonary 
branches.  These  also  anastomose  with  the  symimthctics  to  form 
numerous  plexuses. 

The  terminal  branches  of  the  vagus  are  distributed  to  the  stom- 
ach, solar  plexus,  and  also  to  the  hepatic  plexus  of  the  sympathetic. 

The  most  striking  feature  with  regard  to  the  vagus  is  the  great 
number  of  its  anastomoses.  It  is  a  very  complex  nerve  and  in  no 
part  of  its  course  is  it  exclusively  itself. 

Physiology. — The  relationship  existing  between  the  vagus  and 
spinal  accessory  nerves  is  a  very  intimate  one  by  reason  of  their 
anastomoses.  This  makes  the  determination  of  the  true  nature  of 
the  vagus  one  of  the  difficult  problems  of  physiology. 

It  is  certain  that  the  vagus  is  endowed  with  sensibility,  for  the 
suppression  of  the  spinal  accessory  does  not  deprive  the  parts  of  any 
sensibility  in  any  portion  of  their  common  distribution.  But,  as  the 
spinal  accessory  is  motor  and  the  vagus  sensory,  it  does  not  neces- 
sarily follow  that  the  latter  nerve  is  exclusively  sensory  and  that  all 
movements  realized  by  association  should  be  the  special  work  of  the 
spinal  accessory.  It  was  Bernard  who  first  demonstrated  that  the 
vagus  in  itself  is  a  mixed  nerve.  After  he  had  torn  out  all  of  the 
root-fibers  of  the  spinal  accessory  in  animals  he  found  that  the  motor 
acts  of  the  larynx  persisted  in  the  phenomena  of  respiration.  How- 
ever, while  the  vagus  in  itself  is  a  mixed  nerve  and  has  a  certain 
amount  of  motor  functions,  yet  its  principal  role  is  of  a  sensory 
nature. 

The  mode  of  distribution  of  the  vagus  indicates  that  the  nerve 
exercises  some  action  upon  (1)  the  digestive  apparatus,  (2)  upon  the 
respiratory  apparatus,  (3)  upon  the  circulation,  (4)  upon  the  hepatic 
apparatus,  and  (5)  an  indirect  action  upon  the  kidneys  and  supra- 
renal glands. 

Pathology. — The  recurrent  is  more  liable  to  be  pressed  upon  by 
reason  of  its  peculiar  course  and  its  direct  relations  with  the  great 
vessels  and  body  of  the  thyroid.  As  the  vagus  is  a  mixed  nerve,  it 
is  very  evident  that  compression  causes  troubles  in  motion  and  sensi- 
bility, either  isolated  or  conjointly. 

Any  lesions  located  at  the  origin  of  the  vagus  cause  phenomena 
of  irritation  in  the  whole  sphere  of  distribution  of  this  nerve.  Re- 
flexly  the  vagus  is  capable  of  affecting  the  chorda  tympani  and 
increasing  the  flow  of  saliva.  It  is  for  this  reason  that  intestinal 
parasites  often  cause  ptyalism. 

The  sensibility  of  the  branches  of  the  vagus  in   the  stomach 


CRANIAL  NERVES.  767 

remains  mitonscious  during  the  normal  physiological  state,  when  it 
does  not  seem  to  be  any  greater  than  that  of  the  sympathetic.  Dur- 
ing pathological  conditions,  however,  it  acquires  a  high  degree  of 
intensity.  Thus,  in  simple  wounds  of  the  stomach,  without  haemor- 
rhage or  peritonitis,  the  impression  carried  to  the  medullary  center 
may  be  of  such  a  nature  as  to  cause  rapid  death. 

The  great  frequency  of  gastralgia  is  due  to  an  affection  of  the 
terminal  branches  of  the  tenth  pair.  At  its  cranial  end  this  same 
nerve  is  found  to  be  in  direct  relation  with  the  trigeminus  through 
the  intervention  of  the  gray  tubercle  of  Kolando.  This  fact  un- 
doubtedly furnishes  the  key  to  the  headache  which  so  often  accom- 
panies gastralgia. 

The  vagus  is  the  chief  sensory  carrier  of  the  reflex  movements 
of  circulation  and  respiration.  Thus,  irritation  of  the  renal  and 
hepatic  plexuses  can  produce  vomiting. 

Angina  pectoris  has  its  seat  in  the  cardiac  plexus.  The  sensa- 
tion experienced  is  like  that  seen  in  the  renal  and  hepatic  plexuses 
after  renal  and  hepatic  colic. 

ELEVENTH   PAIR,   OR  SPINAL  ACCESSORY   NERVE. 

The  eleventh  pair  of  cranial  nerves,  the  spinal  accessory,  is  com- 
posed of  two  distinct  parts:  a  spinal  portion  and  an  accessory  por- 
tion. A  group  of  cells  in  the  anterior  horns  of  the  spinal  cord  and 
extending  downward  to  the  sixth  cervical  segment  is  called  the 
accessory  nucleus.  There  is  another  group  of  cells  at  the  exit  of 
the  first  cervical  nerve  which  extends  into  the  medulla  oblongata 
and  is  the  origin  of  the  hypoglossal  nerve.  The  medulla-oblongata 
root  arises  from  the  nucleus  ambiguus,  which  is  connected  with  the 
vagus  nucleus  in  the  medulla. 

The  superficial  origin  of  the  accessory  portion  is  from  the  groove 
between  the  inferior  olive  and  the  restiform  body.  Near  the  jugular 
foramen  both  portions  come  together,  but  do  not  exchange  fibers. 
Very  soon  both  roots  separate  from  one  another  to  form  the  two 
distinct  branches. 

The  accessory  portion  of  the  nerve  passes  entirely  into  the  plexus 
gangliformis  of  the  vagus.  This  branch  supplies  the  vagus  with  the 
major  portion  of  its  motor  fibers  and  also  its  cardio-inhibitory  fibers. 

The  spinal  portion  enters  the  cavity  of  the  cranium  by  passing 
through  the  foramen  magnum.  The  two  portions  of  the  spinal 
accessory  leave  the  cranium  together  by  passing  through  the  middle 
compartment   of   the   jugular  foramen.     The    spinal   portion    then 


768  PHYSIOLOGY. 

pierces  the  sterno-mastoid  to  supply  it  and  the  trapezius.  This  por- 
tion oi'  the  nerve  comniuuicates  with  several  cervical  nerves. 

Physiology. — The  eleventh  nerve  is  generally  considered  to  be 
motor.  Any  observable  sensibility  must  be  due  to  anastomosis  with 
the  cervical  nerves. 

From  experimentation  it  has  been  found  that  the  accessory 
branch  presides,  through  motor  branches  in  the  vagus  to  the  laryn- 
geal muscles,  over  the  formaiioii  of  sound  and  its  tone.  The  spinal 
branch  is  concerned  in  the  duration,  intensity,  and  modulation  of 
the  vocal  sound.     Hence  it  regidates  the  rhythm  of  speech  and  song. 

Aphonia  is  often  due  to  hysteria,  but  may  be  due  to  lead-poison- 
ing, syphilis,  or  to  such  reflex  causes  as  intestinal  worms.  The  reflex 
that  is  established  between  the  vocal  and  genital  organs  is  also  shown 
by  troubles  in  the  spinal  branch  of  the  spinal  accessory.  The  voice 
may  be  lost  at  times  during  menstruation. 

TWELFTH  PAIR,  OR  HYPOGLOSSAL  NERVE. 

The  nuclei  of  the  hypoglossal  nerve  are  under  the  floor  of  the 
fourth  ventricle,  on  each  side  of  the  raphe.  Beneath  the  main 
nucleus  of  the  hypoglossal  nerve  is  a  collection  of  cells  in  the  for- 
matio  reticularis,  called  the  hypoglossal  nucleus  of  Roller. 

Cortical  Connection. — The  motor  path  is  from  the  inferior  part 
of  the  central  convolutions. 

Anastomoses. — The  connections  of  the  hypoglossal  are:  1.  With 
the  superior  cervical  ganglion  of  the  sympathetic,  which  supplies 
vasomotor  fibers  to  the  vessels  of  the  tongue.  2.  The  plexus  gangli- 
formis  vagi  gives  a  small  lingual  branch  which  supplies  the  tongue 
with  sensory  fibers.  3.  The  hypoglossal  is  also  connected  with  the 
upper  cervical  nerves. 

Physiology. — The  hypoglossus,  by  itself,  is  purely  motor.  It 
moves  the  muscles  of  the  tongue.  When  its  original  filaments  are 
torn  out  there  is  never  any  pain.  Sensibility  of  its  terminal  branches 
is  due  to  anastomoses  with  the  lingual.  When  the  hypoglossus  is 
cut,  the  tongue  remains  quiescent  in  the  mouth. 

In  unilateral  paralysis  of  the  hypoglossus  the  tongue,  when  pro- 
truded, passes  over  to  the  paralyzed  side.  This  phenomenon  is  occa- 
sioned by  the  action  of  the  genio-hyo-glossus  of  the  sound  side. 

Literature  Consulted. 

Gordinier,  "Nervous  System." 


CHAPTER  XXI. 

REPRODUCTION. 

All  physiological  phenomena  described  in  the  previovxs  chapters 
have  as  their  ultimate  result  the  maintenance  of  the  life  of  the 
individual  itself.  Xo  matter,  however,  with  what  regularity  these 
physiological  processes  are  taking  place,  the  life-period  of  a  given 
animal  is  not  of  an  unlimited  duration.  Sooner  or  later  the  more 
or  less  complicated  mechanism  stops  its  activity,  and  the  individual 
ceases  to  exist.  With  its  death,  not  only  all  traces  of  the  former 
existence  of  the  individual,  but  also,  with  it,  the  existence  of  the 
entire  species  to  which  the  individual  belonged,  would  be  entirely 
Aviped  out,  had  nature  not  j^rovided  for  a  process  of  rejuvenation,  as 
it  were,  of  all  living  beings.  This  very  important  and  peculiar  phe- 
nomenon in  the  economy  of  all  living  organisms,  animal  as  well  as 
plant,  is  generally  known  as  the  process  of  Reproduction,  the  ulti- 
mate aim  of  which  is  to  maintain  the  species.  We  have  to  confine 
ourselves  to  a  consideration  of  animal  reproduction  only,  and,  even 
here,  we  find  this  important  ju'ocess  carried  out  in  various  ways.  In 
lower  animals,  in  which  a  specialization  of  different  parts  of  the  body 
to  different  functions  is  not  yet  established,  the  process  of  reproduc- 
tion is  also  more  or  less  simple.  The  body  of  an  amoeba  becomes 
constricted  and  finally  is  divided  in  two  halves,  and  each  of  these 
halves  becomes  a  fully  developed  animal,  capable  of  multiplying  in 
the  same  fashion.  A  portion  of  a  hydra,  separated  from  the  living 
animal,  is  capable  of  developing  into  a  complete  new  hydra.  This 
method  of  reproduction  is  called  non-sexual. 

Throughout  the  greatest  part  of  the  animal  kingdom,  Avhere  we 
find  well-defined  physiological  division  of  labor  in  regard  to  other 
vital  functions,  we  also  find  the  function  of  laying  the  foundation 
for  perpetuating  the  species  assigned  to  special  parts — organs  of 
■reproduction.  The  product  of  these  specialized  organs  is  known  in 
modern  biology  as  the  germ-plasm,  and  it  is  upon  this  structure  that 
the  formation  of  a  new  individual  and  the  transmission  of  all  the 
qualities  from  the  parents  to  the  offspring — the  liereditij — are  con- 
sidered to  depend.  The  starting  point  for  the  development  of  every 
individual  we  find  represented  in  a  typical  cell,  called  an  ovum,  con- 
taining  the   germ-plasm,'  and    therefore    also    called    germinal    cell. 

^9  (7G9) 


770  PHYSIOLOGY. 

There  are  a  few  instances,  however,  in  which  tlie  ovum  alone  is 
capable  of  reproducing  a  new  individual.  This  is  observed  only 
among  lower  animals,  and  this  method  of  reproduction  is  known  as 
parthenogenesis.  In  all  more  highly  organized  animals  the  ovum  is 
not  capable  of  developing  into  a  new  individual,  unless  it  comes  in 
contact  and  fuses  with  a  part  of  another  germinal  cell  called  a  sper- 
matozoon.    This  method  is  called  sexual  reproduction.     In  it  the  ovum 


Fig.  .378. — Graafian  Follicle  from  Ovary  of  a  New-born  Child. 
(After  P.  Strassmax.) 

It  consists  of  five   portions:      (1)   An   external   membrane  or   zona  peUucida. 

(2)  An   Internal   membraru?    or   vitelline   membrane    which    lies    in    close    to    the 
.    yelk;     between   the   two  membranes   is   a   slight   space,   the   peri-vitelline   space. 

(3)  The  yelk  or  vitellus,  containing  yelk  grains  or  dentoplasm.  (4)  The  nucleus, 
germinal  vesicle,  vesicle  of  Purkinje.  (5)  The  nucleolus,  germinal  spot,  spot  of 
Wagner,   consisting  mainly  of  chromatin. 

presents  the  female  element,  the  spermatozoon  the  male  element  of 
reproduction.  The  process  of  meeting  and  ultimate  fusion  of  the 
two  elements  to  form  one,  capable  of  forming  a  new  individual,  is 
called  fertilization. 

The  fact  that  in  producing  a  new  individual  a  union  of  male 
and  female  elements  takes  place  has  been  known  for  centuries ;  but 
in  regard  to  the  importance,  or  the  predominating  influence,  of  the 
one  or  the  other  of  these  elements,  the  views  have  changed.     During 


REPRODUCTIOX. 


771 


the  eighteenth  and  part  of  the  nineteenth  centuries,  we  find  among 
investigators  and  interpreters  of  this  phenomenon  two  extreme  views 
represented.  Some  investigators  considered  the  spermatozoon  as  a 
very  minute  hut  complete  animal — animalculus — containing  all  the 
organs  of  its  jDarent  animal  en  miniature.  By  means  of  a  slender 
tail  they  were  supposed  to  move  around  until  they  found  an  appro- 
priate soil — the  ovum — to  which  they  became  attached  and  from 
which  they  received  the  necessary  stimulus  to  grow,  and  gradually 
attained  the  size  characteristic  to  the  type.  The  advocates  of  this 
view  have  been  known  as  animalculists. 

The  advocates  of  the  other,  extremely  oppo- 
site, view — the  ovists — considered  the  ovum  to  be 
like  the  bud  of  the  plant,  containing  all  the  parts 
of  the  future  animal  wrapped  together,  and,  being 
met  by  the  spermatozoon,  the  parts  received  a 
stimulus  for  their  unfolding  and  growth  until  the 
typical  size  has  been  reached.  It  is  obvious  that 
these  both  extreme  views  are  based  on  a  common 
supposition  that  either  the  spermatozoon  or  the 
ovum  represents  an  already  preformed  organism, 
and  therefore  l^oth  of  these  views  have  accord- 
ingly been  known  as  the  theory  of  preformation. 
A  detailed  account  of  other  theories  on  this  sub- 
ject is  generally  given  in  text-books  of  embr}'- 
ology.  For  the  understanding  of  the  physiology 
of  reproduction,  it  suffices  to  state  that  subsequent  Fig.  379. — Human 
investigations  have  proven  conclusively  that  Spermatozoon, 
the  ovum  as  well  as  the  spermatozoon  repre-  ^^  antox.j 
sent  but  single  cells.  Simultaneously  with  the  astonishing  facts, 
revealed  during  the  last  few  decades,  of  the  structure  and  life-his- 
tory of  the  cell  in  general,  which  are  presented  in  the  first  chapter 
of  this  book,  very  much  light  has  been  thrown  on  the  structure  and 
life-history  of  the  cellular  elements  specialized  for  reproduction. 
According  to  the  facts  known  at  the  present  time,  it  is  pretty  well 
establislied  that  both  the  spermatozoon  and  the  ovum  originate  from 
the  same  source,  the  germinal  epithelium :  both  undergo  a  prelim- 
inary process  of  ripening,  matvrafion,  before  they  are  able  to  par- 
ticipate in  fertilization ;  and,  while  the  role  assigned  to  one  of  them 
in  the  latter  process  is  not  exactly  the  same  as  the  role  assigned  to 
the  other,  they  are  nevertheless  equivalents  in  regard  to  their  ultimate 
significance  for  the  process  of  producing  a  new  individual. 


772  PHYSIOLOGY. 

To  fully  appreciate  the  different  stages  of  the  process  of  repro- 
duction mentioned  above,  a  brief  account  of  the  origin,  formation, 
and  structure  of  the  ovum  and  spermatozoon  is  essential. 

The  beginning  of  the  differentiation  of  the  organs  of  the  animal 
body  from  the  blastoderm,  of  which  we  will  speak  later,  we  find 
expressed  in  the  arrangement  of  tlie  building  material,  so  to  speak, 
in  three  distinct  so-called  germinal  layers — an  outer  layer,  the  ecto- 
derm; an  inner  one,  the  entoderm;  and  between  these  two  a  middle 
layer,  the  mesoderm.  The  first  two  layers  we  find  very  well  defined 
in  all  Metazoa,  and  from  them  all  vital  organs  of  the  body,  composed 
of  epithelium,  are  developed.  The  middle  layer  supplies  the  sup- 
porting and  connective  tissues  and  the  vascular  system.  In  the 
lower  types  of  Metazoa,  which  require  very  little  supporting  material, 
and  in  which  a  special  vascular  system  is  not  present,  we  find  also 
the  mesoderm  very  scantily  presented.     The  higher  the  type  of  the 


Fig.   380. — Transection   of   Chick  Embryo,   Showing  the   Three 
Plastodennic  Layers.      (Mantox.) 

animal,  the  more  we  find  the  mesoderm  developed,  until  we  finally 
see  it  not  only  as  a  well-defined  single  layer,  but  it  becomes  split 
into  two  secondary  layers :  one,  the  parietal  mesoderm,  which  follows 
and  gives  support,  and  supplies  blood-vessels  and  nerves  to  the 
ectoderm  and  its  derivatives,  and  a  second  one,  the  visceral  mesoderm, 
which  acts  in  the  same  way  for  the  entoderm.  The  space  formed 
between  them  constitutes  the  future  body  cavity  or  coelom.  It  is 
in  this  middle  layer  where  we  find  the  first  traces  of  the  two  kinds 
of  the  elements  of  reproduction — the  spermatozoa  and  ova.  In  the 
lower  types,  with  scanty  mesoderm,  we  find  these  elements  loosely 
scattered  within  it;  in  the  higher  types,  with  well-defined,  double- 
layered  mesoderm,  we  find  certain  parts  of  it  crystallized,  so  to 
say,  as  organs  of  reproduction — the  ovaries  and  testicles.  It  was 
Waldeyer  who  first  called  attention  to  the  fact  that  a  certain  part 
on  the  visceral  layer  of  the  mesoderm  becomes  thickened  and  forms 
the  so-called  genital  ridge,  which  gives  rise  to  the  organs  of  the 
primitive  genito-urinary  apparatus.     A  part  of  the  ridge-cells  be- 


REPRODUCTION.  773 

comes  the  above-mentioned  germinal  epithelium  of  Waldeyer,  because 
it  is  these  cells  which,  by  their  down-growth  into  the  subjacent 
layers,  gradually  become  transformed,  first,  into  indifferent  sexual 
cells,  and.  ultimately,  into  spermatozoa  or  ova,  as  the  case  may  be. 
Leaving  out  the  detailed  account  of  the  development  of  the  testicle  and 
ovary,  to  be  found  in  text-books  on  embryology,  we  have  to  consider 
the  formation  of  the  spermatozoa  and  ova  as  it  takes  place  in  a  fully 
developed  ovary  or  testicle.     In  the  seminiferous  tubules  of  the  testi- 


ng. 381. — Diagram  Showing  Development  of  Spermatozoa  in  a  Seminal 
Tubule.     (McMuRRiCH.) 

1,  Spermatozoon.      2,  Spermatid.      3,  Secondary    spermatocyte.      4,  Primary    sper- 
matocyte.    5,  Spermatogone.     6,  Supporting   cell. 

cle  we  find  five  physiologically  different  kinds  of  cells.  Covering 
the  inner  surface  of  the  basement  membrane  of  the  tubule  we  find 
the  so-called  layer  of  parietal  cells,  consisting  of  two  kinds  of  cells, 
of  a  different  physiological  character:  (1)  the  sustentacular,  and  (2) 
the  spermatogenic  cells.  Both  kinds  undergo  karyokinetic  multipli- 
cation, but  the  fate  of  their  offspring  is  different.  Each  offspring 
of  a  sustentacular  cell,  after  attaining  its  full  size,  is  not  only  mor- 
phologically, but  also  physiologically,  fully  equivalent  to  the  parent 
cell,  as  it  is  ready  to  serve  its  ultimate  definite  purpose — supporting 
and  generallv  uniting  with  other  cells  of  its  kind,  it  forms  stronger 


774 


PHYSIOLOGY. 


supporting  units,  the  so-called  columns  of  Sertoli.  In  regard  to  the 
spermatogenic  cells,  we  see  an  entirely  different  state  of  affairs.  The 
function  of  each  spermatogenic  cell  is  nothing  else  but  to  undergo 


•   •       4- .^  4 

Fig.  382. — Schema  to  Indicate  the  Process  of  Maturation  of  the 

Spermatozoa.     (  Boveri.  )      (  Howell.  ) 

1,  Primary  spermatocytes.    2,  Secondary  spermatocytes.    3,  Spermatids.    4,  Spermatozoa. 


Fig.  383. — Diagram  Showing  Essential  Facts  in  the  Maturation 
of  the  Egg.     (Wilson.) 

1,  First  polar  body.      2,  Division  of  tirst  polar  body.      3,  Three  polar  bodies.      4,  Female 

pronucleus. 

karyokinesis  and  form  two  cells,  called  mother-cells.  Each  mother- 
cell  performs  the  similar  function  and  gives  rise  to  two  other  cells^ 
called  daughter-cells ;  hut  these  cells  differ  from  their  two  consecu- 
tive   predecessors.     They    do    not    multiply    further,    but    in    the 


REPRODUCTIOX.  775 

material  constituting  their  structure  a  rearrangement  takes  place, 
and  gradually  each  of  these  daughter-cells  becomes  transformed  into 
a  spermatozoon,  with  its  characteristic  parts :  the  head,  middle  piece, 
and  tail.  It  is  evident,  therefore,  that  each  spermatogenic  cell  gives 
rise  to  four  spermatozoa,  all  equally  qualified  to  take  part  in  the 
physiological  process  assigned  to  them — fertilization.  This  is  dia- 
gramatically  represented  in  the  figure  of  Boveri  (Fig.  382). 

In  the  ovary  we  find  the  Graafian  follicle,  containing  two  dif- 
ferent kinds  of  cells:  one  large  one,  the  ovarian  ovum,  correspond- 
ing to  the  spermatogenic  cell  of  the  testicle;  and  more  numerous 
smaller  ones,  supporting  or  protecting  the  larger  by  forming  a  cap- 
sule, as  it  were,  around  it  and  constituting  the  memlrana  granulosa 


i 
Fig.  384. — Schema  to  Indicate  Process  of  jMaturation  of  Ovum. 
,  (BovERi. )      (Howell.) 

1,  Ovarian  egg.    2,  First  polar  body.    3,  Abortive  ova  resulting  from  division  of  first  polar 
body.    4,  Second  polar  body,  abortive  ovum.     5,  Mature  egg. 

with  its  discus  proligerus.  Like  the  spermatogenic  cell,  the  ovarian 
ovum  also  undergoes  the  karyokinetic  division,  but  with  somewhat 
different  result.  We  find  two  cells  formed,  one  of  which  is  very  large 
and  contains  the  chromatin  substance  and  the  cytoplasm  in  the  same 
proportion  as  the  egg  cell,  and  another,  which  is  very  small  and  con- 
tains only  chromatin,  and  little  cytoplasm.  A  second  division  of 
the  larger  cell  takes  place,  with  the  same  result,  forming  again  one 
large  cell  and  one  very  small  one.  The  first  small  cell,  in  the  mean- 
time, frequently  also  divides  in  two,  and,  because  the  three  small 
cells  are  found  grouped  together  on  one  of  the  poles  of  the  large 
cell,  they  received  the  name  polar  bodies.  They  take  no  part  in  the 
processes  following,  and  gradually  disappear.  The  large  remaining 
cell  is  the  mature  ovum,  the  one  which  is  qualified  for  fertilization, 
and  the  series  of  changes  through  which  the  ovarian  ovum  has  to 
pass  to  become  so  qualified  is  called  maturation.  The  parallelism  in 
the  changes  which  take  place  during  formation  of  the  two  sexual 


77G 


PHYSIOLOGY. 


Fig.  385. — Schematic  Representation  of  the  Processes  Occurring  During 
Cell-division.      (Boveri.)      (Howell.) 


REPRODUCTION.  777 

cells  are  very  lucidly  represeutcd  by  Boveri  in  the  two   schematic 
figures   (Figs.  3S5  and  380). 

The  process  of  maturation  is  also  called  reduction  division, 
because  it  is  known  at  present  that  the  quantity  of  chromatin  sub- 
stance in  the  nucleus  of  either  of  the  sexual  cells,  or  the  number  of 
chromosomes  which  the  chroma-tin  thread  forms,  is  reduced  to  one- 
half  of  the  quantity  typical  to  all  other  cells  of  the  same  animal. 
In  regard  to  other  essential  parts,  we  find  the  spermatozoon  contain- 
ing only  very  little  cytoplasm,  while  the  mature  ovum  contains  nearly 
all  the  cytoplasm  of  the  original  ovarian  ovum.  The  centrosome 
is  considered  by  Boveri  to  become  lost  in  the  ovum,  while  in  the 
spermatozoon  it  is  retained,  and  later  plays  an  important  part.  The 
process  of  fertilization  itself  consists  in  a  union  of  the  male  with 
the  female  element  to  form  one  capable  of  being  the  foundation  for 
a  new  individual,  although  in  regard  to  the  details  of  this  process 
the  facts  known  at  present,  and  the  interpretations  given,  can  by 
no  means  be  considered  conclusive.  A  very  widely  and  favorably 
accepted  view  is  presented  by  Boveri  in  a  to  g  (Fig.  386),  and  the 
essential  points  are  the  following:  either  attracted  by  chemotaxic 
force  radiating  from  the  ovum,  or  by  their  own  locomotion,  the  sper- 
matozoa come  in  contactwith  the  ovum  and  pierce  the  zona  radiata; 
but  as  soon  as  one  spermatozoon  penetrates  into  the  cytoplasm  of  the 
ovum,  a  reaction  on  its  surface  takes  place,  making  it  impermeable  for 
other  spermatozoa.  During  its  entrance  into  the  ovum,  the  spermato- 
zoon usually  loses  the  tail,  while  the  head,  which  in  reality  repre- 
sents the  chromatin  substance  of  the  nucleus,  becomes  expanded, 
takes  on  the  character  of  a  nucleus,  and  moves  towards  the  nucleus 
of  the  ovum.  The  egg  at  this  stage  obviously  contains  two  nuclei; 
the  one  is  called  male  pronucleus,  and  the  other  female  pronucleus. 
Gradually  both  come  in  contact  and  form  the  so-called  segmen- 
tation nucleus.  The  middle  piece  of  the  spermatozoon  also  enters 
the  ovum.  Soon,  however,  it  reveals  itself  as  a  centrosome  and  acts 
as  a  dynamic  force  for  a  cleavage  of  the  segmentation  nucleus,  which 
inaugurates  the  process  of  cell-division.  With  this  first  cleavage  the 
formation  of  a  new  individual  has  actually  begun.  Through  succes- 
sive cell-divisions  an  aggregation  of  cells  is  finally  formed,  which, 
depending  on  the  amount  of  nutritive  material  stored  up  in  the  ovum 
for  future  purposes,  becomes  arranged  either  in  form  of  a  spherical 
mass  (morula),  which  gradually  becomes  hollow  and  is  then  called  a 
lilastula,  or  as  a  circular  disk,  and  in  either  case  a  uniform  layer 
of   cells   is   gradually  formed,   which   is   known    as    the   hlastoderm. 


778 


PHYSIOLOGY. 


Fig.  386. — Schematic  Reiiresentation  of  the  Processes  Occurring 
During  the  Fertilization  and  Subsequent  Segmentation  of  the  Ovum. 
The  chromatin  (chromosomes)  of  the  ovum  is  represented  in  blue,  that 
of  the  spermatozoon  in  red.      (Boveki. )      (Howell.) 


REPRODUCTION.  779 

Through  invagination  of  the  blastula,  forming  the  cnp-shaped  gas- 
trula,  or  through  delaniination  from  the  disklike  layer  of  cells,  a 
blastoderm  is  gradually  formed,  which  consists  of  two  distinct  layers, 
an  outer  one,  called  ectoderm,  and  an  inner  one,  called  entoderm. 

The  next  step  of  advancement  in  the  development  is  one  to 
which  the  attention  of  all  distinguished  embryologists  has  been  kept 
engaged  for  many  decades.  It  is  the  gradual  formation  of  a  distinct 
tliird  layer  of  cells  between  the  outer  two,  which  is  called  the  middle 
layer,  or  mesoderm.  Some  investigators  have  proved  that  in  certain 
animals  the  mesoderm  originates  from  the  entoderm;  others,  again, 
have  shown  that  it  takes  its  origin  from  the  ectoderm.  The  present 
state  of  our  knowledge  leads  us  to  assume  that  from  the  morpholog- 
ical point  of  view  throughout  the  animal  kingdom  both  modes  of 
origin  can  be  found  to  take  place.  The  far  more  important  phy- 
siological aspect  and  significance  of  the  question  is  closely  correlated 
with  the  broader  questions  of  general  biolog}',  and  to  them  we  will 
turn  our  attention  now. 

With  the  differentiation  of  blastoderms  into  three  distinct,  so- 
called  germinal  layers,  the  foundation  for  a  physiological  division 
of  labor  is  established  and  the  formation  of  the  various  organs — 
organogenesis — begins.  A  description  of  the  details  of  it,  however, 
are  beyond  the  scope  of  this  text-book.  Here  it  is  only  necessary 
to  emphasize  the  important  fact  that  each  of  the  three  layers  repre- 
sents not  only  a  morphological,  but  also  a  physiological,  unit,  as  each 
one  of  them  gives  rise  only  to  certain  tissues  and  organs  of  the  adult, 
and  neither  one  can  be  substituted  in  that  respect  by  another  with- 
out producing  abnormal  conditions.  This  fact  is  of  such  great  prin- 
cipal significance  that  pathologists  have  adopted  a  classification  of 
tumors  according  to  the  three  germinal  layers  and  their  derivates. 

An  exceedingly  important,  as  well  as  interesting,  question  which 
occupies  the  minds  of  modern  biologists  is  v/hether  the  physiological 
differentiation  of  the  germinal  layers  begins  only  with  the  forma- 
tion of  these  structural  units,  or  whether  it  is  already  present  at  an 
earlier  stage  of  the  development  of  the  ovum,  and  becomes  more  per- 
ceivable only  in  the  germinal  layers.  The  attempt  to  answer  this  ques- 
tion leads  us  over  to  the  consideration  of  the  vital  problems  in 
general  biolog}' — evolution  and  inheritance — which  I  will  shortly 
take  up.* 

It  has  been  shown  bv  Loeb  that  the  unfertilized  egs;  of  the  sea 


*  The  preceding  pages  \ipon  reproduction  have  been  contributed  by  Dr. 
P.  Fischelis. 


780  PHYSIOLOGY. 

urchin  can  develop  by  chemical  agents  without  spermatozoa.  He 
treats  the  egg  for  a  minute  or  more  with  acetic  acid,  to  cause  a 
membrane  to  form  around  it.  They  are  then  deposited  in  a  hyper- 
tonic sea-water,  made  by  the  addition  of  sodium  cliloride  to  ordinary 
sea-water.  Afterwards  they  are  transferred  to  ordinary  sea-water, 
and  soon  they  multiply  and  develop  into  normal  larvae.  Loeb  be- 
lieves that  the  unfertilized  egg  of  the  sea  urchin  possesses  all  the 
elements  for  development,  and  the  only  reason  parthenogenesis  in 
it  is  prevented  is  the  constitution  of  the  sea-water.  Here  the  pro- 
cess is  mainly  ionic.  He  believes  that  the  nucleus  of  the  sperma- 
tozoon is  not  essential,  and  that  it  is  only  a  means  to  stimulate  the 
arrangement  of  ions  surrounding  it. 

How  does  the  ovum  arrive  in  the  uterus?  There  is  consider- 
able obscurity  on  this  point.  Most  observers  believe  the  ovum  is 
discharged  into  the  pelvic  cavity,  where  the  cilia  of  the  Fallopian 
tube  propel  it  toward  the  uterus.  It  is  in  the  tube  that  the  sper- 
matozoon meets  the  ovum,  which  here  undergoes  fecundation,  arrives 
in  the  uterus,  and  develops.  The  spermatozoon  is  deposited  in  the 
vagina  or  at  the  mouth  of  the  uterus,  and,  by  means  of  its  cilium  or 
tail,  travels  up  the  uterus  and  Fallopian  tube. 

Should  the  ovum  not  be  impregnated,  it  dies  and  passes  out  of 
the  uterus  as  a  constituent  of  its  secretions.  On  the  other  hand, 
should  it  become  fecundated,  the  ovum  becomes  attached  to  the 
mucous  membrane  of  the  uterus,  usually  occupying  the  bottom  of 
some  little  cleft  or  pouch. 

The  investigations  of  Peters,  of  Vienna,  and  of  Webster,  of  Chi- 
cago, show  that  the  uterine  mucosa  does  not  fold  up  around  the 
ovum,  but  that  the  mucosa  at  the  site  of  implantation  is  eroded;  so 
that  the  ovum  eats  its  way,  as  it  were,  into  the  mucosa,  sinking  into 
its  depths  until  the  edge  of  the  swollen  mucosa  closes  over  it,  thus 
forming  the  decidua  reflexa. 

The  position  to  which  the  fecundated  egg  becomes  attached  is 
the  decidua  serotina,  and  it  eventually  forms  the  placenta,  the 
nutrient  organ  of  the  embryo.  Before  the  ovum  arrives  in  the 
uterus  it  has  formed  the  amnion  and  chorion  with  the  villi  of  the 
chorion.  Some  of  the  ectodermal  cells  in  the  chorion  become  spe- 
cialized to  form  what  is  called  the  trophoblast,  and  this  probably 
transfers  nourishment  from  the  mother  to  the  ovum. 

After  its  formation  the  mesoderm  grows  by  reason  of  its  own 
cell-proliferation,  and  is  independent  of  its  dual  source.  Along 
either  side  of  the  median  line  the  luesoderm  presents  a  thickening 


REPRODUCTION. 


781 


of  cells  (vertebral  plate),  which  becomes  laminated  laterally  (lateral 
plate).  From  the  vertebral  plate  develop  the  somites;  the  lateral 
plate  splits  into  two  lamella?,  of  which  the  outer  is  the  somatic  meso- 
derm; the  inner,  the  splanchnic  mesoderm. 


Fig.  38S. 

Fig.  387. — Formation  of  Decidua  (the  decidua  is  colored  black,  the 
ovum  is  represented  as  engaged  between  two  projecting  folds  of  mem- 
brane).     (After  Dalton.) 

Fig.   388. — Projecting  Folds  of  ^lembrane  Growing  Around   the   Ovum. 
(After  Daltox.) 

Fig.  389. — Showing  Ovum  Completely  Surrounded  by  the  Decidua 
Reflexa.      (After  Daltox.) 

The  former  iinites  with  the  ectoderm  to  form  the  somafopleure, 
while  the  latter  unites  with  the  entoderm  to  form  the  splanchnopleure. 
Between  the  somatcpleure  and  the  splanchnopleure  there  is  an  open- 
ing, the  tody-cavity,  from  which  arise  the  serous  cavities  of  the  adult. 


782  PHYSIOLOGY. 

Derivatives  from  the  Layers. 

Ectoderm,  or  Epiblast. — From  the  epiblast  are  developed  the 
central  nervous  system  and  the  epidermal  tissues. 

Mesoderm,  or  Mesoblast. — From  the  mesoblast  arise  most  of  the 
organs  of  the  body.  These  include  the  vascular,  muscular,  and 
skeletal  systems;  also  the  generative  and  excretory  organs;  but  not 
the  bladder,  the  first  part  of  the  male  urethra,  nor  the  female  urethra. 

Entoderm,  or  Hypoblast. — The  hypoblast  is  the  secretory  layer. 
From  it  spring  the   intestinal   epithelium   and   that   of  the   glands 


b.  8. 


All. 


Fig.  390. — Diagram  of  an  Early  Stage  of  a  Primate  Embryo.     ( MixOT. ) 

AU,   Allantois.     Am,   Amnion,     h.s..    Body-stalk.     Clio,    Chorion.     Emi),    Embryo. 
In,  Entodermal  Cavity  of  Embryo,     ri,  Villi  of  Chorion.     //A",   Yelk-sac. 

which  open  into  the  intestines;  also  the  epithelum  of  the  resipra- 
tory  system,  the  bladder,  the  prostatic  part  of  the  male  urethra,  and 
the  entire  female  nrethra. 

Up  to  this  point  the  cavity  of  the  germ  is  one  undivided  com- 
partment bounded  by  splanchnopleure.  By  infolding  of  the  splanch- 
nopleure  this  cavity  is  divided  into  two  smaller  compartments  of 
unequal  size.  The  smaller  is  the  gut-trad;  the  larger,  the  yelk-sac, 
or  umbilical  vesicle.  The  communication  between  the  two  cavities  is 
the  vitelline  duct. 

With  the  unfolding  of  the  splanchnopleure  the  somatopleure 
also   follows,  to  form   the  body-walls   of  the  embryo.      Part  of  the 


REPRODUCTION.  783 

somatopleure  becomes  so  lifted  up  as  eventually  to  curl  up  and  over 
the  embryo  until  the  fold  of  one  side  fuses  with  that  of  the  other. 
That  is,  there  is  formed  the  amniotic  membrane  and  cavity.  The 
amnion  is  a  membranous  sac  consisting  of  two  layers  of  embryonal 
cells.  The  inner  layer  is  composed  of  ectodermic  cells,  the  outer 
layer  of  mesodermic  cells.  The  false  amnion,  or  serosa,  comprises 
all  that  part  of  the  somatopleure  which  does  not  go  to  form  the 
body-wall  and  the  true  amnion.  It  is  also  called  the  primitive 
chorion  and  by  some  authors  the  chorion.  The  allantois  growing 
forth  from  the  gut-tract  unites  with  its  inner  surface  and  thus  gives 
it  vascularity.  It  is  the  outermost  envelope  of  the  germ.  The 
amniotic  sac  is  tilled  with  a  fluid  in  which  floats  the  foetus. 

The  function  of  the  yelk-sac  is  to  furnish  nutrition  to  the 
embryo  for  a  certain  length  of  time,  but  is  very  rudimentary  in  man. 
As  the  yelk-sac  disappears  by  degrees,  its  place  is  taken  by  the 
aUaniois.  The  latter  then  serves  as  a  medium  of  nutrition  and 
respiration  until  the  formation  of  the  placenta  at  the  end  of  the 
third  month. 

Chorion. — The  chorion  is  the  membrane  which  envelops  the 
ovum  subsequent  to  the  appearance  of  the  amnion.  It  results  from 
the  fusion  of  the  allantois  and  false  amnion. 

Upon  the  surface  of  the  chorion  are  numerous  villi.  At  first 
they  are  uniform  in  size,  but  at  the  latter  half  of  the  first  month 
there  develops  an  area  the  villi  of  w^hich  are  noted  for  their  long 
prolongations:  the  chorion  frondosum.  This  eventually  becomes  a 
portion  of  the  placenta.  The  remaining  villi  atrophy  and  finally 
disappear. 

Chemical  Constituents  of  Spermatozoa. — In  the  head  of  the 
spermatozoa  of  salmon  of  the  Khine  is  found  a  chemical  body  which 
is  a  combination  of  nucleic  acid  and  a  protamin.  In  different  fishes 
the  protamin  is  given  a  dift'erent  name.  Thus,  we  have  scrombrin 
from  scromber  scrombrius.  salmin  from  salmon,  clupein  from  herring 
(clupea  harengus),  sturin  from  sturgeon  (accipenser  sturo).  The 
protamins  are  strong  bases  and  their  watery  alkaline  solutions  are 
intensely  akaline,  and  with  acids  they  form  characteristic  salts. 
They  all  give  the  biuret  reaction,  and,  it  is  to  be  noted,  without 
the  addition  of  an  alkali.  Protamins  are  not  coagulated  by  heat, 
and  polarize  to  the  left.  These  peculiarities  place  the  protamins  in 
a  class  peculiar  to  themselves.  Clupein,  chemically,  is  identical, 
according  to  Kossel,  with  salmin. 

A  peculiarity  of  the  protamins  is  the  high  percentage  of  nitro- 


784  PHYSIOLOGY. 

gen;  in  salmon  it  forms  nearly  a  third  of  the  whole  weight.  By 
breaking  np  the  protamins  by  acids  it  was  found  that  the  chief  ele- 
ment in  the  protamins  is  arginin,  with  the  hexone  bases.  In  the 
semen  of  the  carp  (cyprinus  carpio)  Miescher  obtained  no  protamin, 
but  a  "peptonelike"  substance  with  Ijasic  properties  which  is  a  histon, 
which  makes  bases  very  easily  with  acids.  The  histon  possesses  the 
usual  properties  of  the  albumins. 

The  nucleo-proteids  in  the  heads  of  all  spermatozoa  are  a  nucleic 
acid  compound.  The  nucleic  acids  of  sperm  a?e  organic  phosphoric 
acid  combinations.  The  protainins  and  histon  have  been  found  only 
in  the  semen  of  some  fishes,  and  not  in  that  of  mammals. — Burian — 
Asher  und  Spiro's  Ergebnisse  der  Physiologic,  Part  I,  I'JU-i. 

Erection. — The  erectile  tissue  of  the  male  is  formed  by  the 
penis,  formed  of  corpora  cavernosa  and  the  corpus  spongiosum. 
During  erection  the  penis  is  gorged  with  blood,  due  to  the  arterioles, 
which  are  supplied  by  vasodilator  nerves  in  the  nervus  erigens. 
Besides  the  vasodilation,  the  return  flow  of  blood  by  the  dorsal  vein 
is  partially  arrested  by  the  muscle  of  Houston.  The  smooth  mus- 
cles of  the  trabeculge  also  aid  in  the  act  of  erection.  Erection  is  a 
reflex  phenomenon,  and  the  center  is  located  in  the  lumbar  cord.  The 
sensory  nerve  concerned  is  the  pudic,  for  Eckhard  found  that  section 
of  this  prevented,  in  the  dog,  any  erection  when  the  glans  penis  was 
irritated.  Other  irritations,  as  of  the  testes  or  the  prostatic  urethra, 
lead  to  erection.  A  full  bladder  in  the  morning  is  also  frequently 
accompanied  by  a  passive  erection,  due  to  a  compression  of  the  ven- 
ous plexus  of  Santorini  by  the  bladder.  The  genito-spinal  center 
in  the  lumbar  region  is  also  affected  by  impulses  coming  from  the 
brain,  which  may  be  of  two  kinds,  excitatory  and  inhibitory.  The 
penis  also  receives  vasoconstrictor  fibers,  which  emanate  from  the 
second  to  fifth  lumbar  nerves,  and  reach  the  penis  either  l)y  the 
pudic  or  the  hypogastric  plexus.  The  surface  of  the  organ,  its 
integument,  usually  slightly  folded,  becomes  tense,  and  the  engorged 
subcutaneous  veins  are  seen  beneath  the  surface.  During  erection 
the  clonic  contraction  of  the  bulbo-cavernous  muscle  pushes  the 
blood  towards  the  glans.  These  muscles  are  aided  in  a  similar  man- 
ner l)y  the  ischio-cavernous  muscles.  These  two  muscles  have  been 
compared  to  peripheral  hearts  in  the  vascular  movement  of  this 
organ.  In  disease  of  the  spinal  cord  erection  is  often  lost  or  sup- 
pressed, so  that  coitus  is  impossible. 

Ejaculation  of  Semen. — At  the  moment  of  erection  the 
urethral  canal  becomes  filled  with  a  secretion  of  its  different  glands. 


REPRODUCTION.  785 

All  these  glands  and  the  seminal  vesicles  furnish  a  liquid  capable 
of  diluting  and  liquefying  the  semi-solid  semen  as  it  leaves  the  vas 
deferens.  The  smooth  muscles  of  the  vasa  deferentia,  vesiculae 
seminales,  aided  by  the  dartos  and  cremaster  muscles,  which  com- 
press the  testicles,  make  semen  accumulate  in  the  urethra  between 
the  congested  verumontanum  (which  prevents  its  regurgitation  into 
the  bladder)  and  the  urethral  sphincter. 

The  friction  of  the  glans  is  the  cause  of  the  ejaculation.  This 
friction,  in  a  reflex  manner,  causes  the  involuntary  and  spasmodic 
contraction  of  the  vas  deferens  and  of  the  seminal  vesicles. 

The  escape  of  semen  in  jets  is  due  to  the  rhythmic  contraction 
of  the  bulbo-cavernous  and  ischio-cavernous  muscles,  aided  by  the 
other  muscles  of  the  perineum.  Ejaculation  is  accompanied  by  a 
general  excitement  of  the  brain.  However,  Goltz  has  shown  that 
after  a  transverse  section  of  the  cord  in  the  dog,  ejaculation  can  still 
ensue. 

Castration. — In  castrating  a  bull  or  a  guinea-pig  it  is  found 
that  the  thymus  is  greatly  retarded  in  its  stage  of  atrophy,  so  that 
the  thymus  of  an  ox  exceeds  considerably  that  of  a  bull.  The  testes 
greatly  increase  in  size  in  guinea-pigs  after  removal  of  the  thymus. 
Hence  it  is  probable  that  the  thymus  has  an  internal  secretion  which 
controls  the  growth  of  the  testicles. 

Prostate. — The  secretory  nerve  of  the  prostate  gland  is  the 
descending  branch  of  the  inferior  mesenteric  ganglion.  The  vaso- 
dilator fibers  of  the  prostate  are  contained  in  the  nervus  erigens 
and  its  two  branches.  The  vasodilation  of  erection  is  accompanied 
by  a  vasodilation  in  the  prostate.  When  atropin  is  given,  irritation 
of  the  secretory  nerves  of  the  prostate  is  without  effect.  Pilocarpin 
increases  the  secretion. 

Menstruation. — In  the  adult  female  during  certain  age-limits 
there  occurs  a  discharge  from  the  genitalia  once  about  every  twenty- 
eight  days.  This  periodical  discharge  consists  of  blood,  dead  and 
disintegrated  epithelium  from  the  uterus,  and  mucus  from  the  glands 
of  the  uterus. 

With  the  discharge  of  the  above-named  materials  there  is  nsualhj 
expelled  at  the  same  time  one  or  more  ova  from  their  follicles.  How- 
ever, ovulation  and  menstruation  may  be,  and  very  often  are,  inde- 
pendent of  one  another.  The  onset  of  menstruation  is  usually  her- 
alded and  then  accompanied  by  certain  constitutional  signs  of  full- 
ness and  pain  in  the  pelvic  region.     There  is  a  real  congestion  of 

all  of  the  pelvic  organs;  in  particular  the  uterine  mucous  membrane 

&o 


786 


PHYSIOLOGY. 


is  swollen  and  congested.  From  it  are  derived  the  blood  and  epithe- 
lium of  the  menstrual  flux.  By  some  authorities  it  is  claimed  that 
the  entire  uterine  mucous  membrane  is  exfoliated  at  every  flux,  to 
be  regenerated  in  the  interim. 

It  has  been  found  by  observers  that  congestion  of  the  ovary 
coincident  with  sexual  intercourse  is  capable  of  rupturing  Graafian' 
follicles  and  so  liberating  ova.  From  this  it  is  reasonable  to  sup- 
pose that  the  congestion  and  high  tension  of  the  generative  organs 
during  the  time  of  menstruation  would  surely  accomplish  the  same 
end. 


Fig.  391. — Uterus  at  Menstrual  Period,  Showing  Congested  Area 
and  Desti'uction  of  Mucous  Membrane.  (Photomicrograph  by 
Gramm.)     (Gilliam.) 

The  usual  period  of  a  female's  life  during  which  she  menstruates 
is  from  piiherty  (from  the  thirteenth  to  the  fifteenth  year)  to  the 
climacteric,  or  menopause  (about  the  forty-fifth  year).  Its  cessation 
at  the  latter  period  denotes  the  end  of  the  childbearing  period. 

The  cessation  of  menstruation  may  be  abrupt  or  gradual,  and 
is  frequently  accompanied  by  disturbance  of  the  physical  and  the 
mental  functions.  Eemoval  of  the  ovaries  usually  causes  menstru- 
ation to  cease;  occasionally,  however,  menstruation  persists.  If 
after  the  ovaries  are  removed  and  menstruation  has  ceased;  an  ovary- 
is  transplanted,  then  menstruation  returns. 


REPRODUCTION.  787 

Theory  of  Menstruation. — There  are  two  theories.  In 
Pflueger's  theory,  the  discharge  of  blood  is  looked  upon  as  a  phy- 
siological freshening  of  the  tissue,  like  in  surgery,  for  the  recep- 
tion of  the  ovum  and  its  union  with  the  mucous  membrane. 

In  Eeichert's  theory,  before  the  discharge  of  the  ovum  a  change 
takes  place  in  the  uterine  mucous  membrane,  which  becomes  swollen 
up,  more  spongy,  more  vascular,  and  more  ready  to  nourish  an 
impregnated  ovum.  If  the  ovum  is  not  impregnated,  then  there  is 
degeneration  of  the  uterine  mucous  membrane,  and  a  flow  of  blood 
ensues. 

Both  theories  believe  that  menstruation  is  a  preparation  of  the 
uterine  mucous  membrane  for  the  reception  of  the  ovum. 

It  is  usually  recognized  that  ovulation  is  arrested  during  preg- 
nancy and  lactation.  The  amount  of  menstrual  blood  is  usually 
about  IVi;  ounces,  and  the  flow  generally  lasts  four  days. 

Marshall  and  Jolly  have  shown  that  ovulation  cannot  be  the 
cause  of  either  heat  in  animals  or  menstruation.  They  show  that 
the  whole  prooestrous  process  is  of  the  nature  of  a  preparation  for 
the  attachment  of  the  eriibryo  to  the  uterine  mucous  membrane. 
The  ovary  of  a  mammal  elaborates  an  internal  secretion  which,  at 
recurring  j^eriods,  is  the  cause  of  the  proo?strous  and  the  restrous. 
The  corpora  lutea  form  a  ductless  gland,  which  is  necessary  for  the 
nutrition  of  the  trophoblast  during  the  early  stages  of  pregnancy, 
and  subsequently  atrophies. 

Bond  believes  the  endometrium  has  a  saline  secretion  peculiar 
to  the  ancestrous  state;  that  some  substance  is  elaborated  by  the 
pregnant  uterus  which  stimulates  the  growth  of  the  corpora  lutea 
in  transplanted  ovaries.  He  believes  the  ovary  furnishes  a  secre- 
tion having  an  anabolic  influence  on  the  uterus  and  produces  the 
oestrus.  The  saline  uterine  secretion  is  antagonistic  to  the  action 
of  the  ovarian  secretion. 

Corpus  Luteum. — The  place  in  the  ovary  where  the  bursting  of 
a  Graafian  follicle  by  the  overdistension  of  the  liquor  folliculi  ensues 
is  usually  filled  up  with  what  is  known  as  the  corpus  luteum.  The 
follicle  collapses,  and  in  its  interior  remains  a  lining  of  granulosa  cells 
and  a  clot  of  blood.  Cells  of  the  corpus  luteum,  containing  a  yellow 
body  (lutein),  are  formed  from  a  proliferation  of  the  internal  con- 
nective-tissue cells.  If  pregnancy  ensues,  the  true  corpus  luteum  is 
larger,  thicker,  and  deeper  in  color  than  the  false  corpus  luteum  of 
menstruation. 


788 


PHYSIOLOGY. 


Pregnancy. — With  the  impregnation  of  the  ovum  pregnancy 
begins.  Menstruation  is  arrested,  and  nausea  or  morning  sickness 
ensues.  At  the  end  of  the  second  month  the  nipple  swells,  becomes 
more  erect,  and  projects  forward.  Then  the  areola  of  the  nipple 
enlarges,  becomes  puffy,  and  deepens  in  color.  Toward  the  fifth 
month  the  mammary  glands  increase  in  size.  As  to  the  genitals, 
the  mucous  membrane  of  the  vagina  becomes  of  a  violet  hue,  the 
vaginal  part  of  the  cervix  grows  softer,  a  peculiar  velvety  softness 
at  the  end  of  the  third  month.  At  the  end  of  the  third  month  the 
uterus  is  the  size  of  a  foetal  head,  of  certain  doughy,  elastic  feel. 
About  the  sixteenth  week  active  spontaneous  foetal  movements  are 


Fig.  392. — Virginal  Uterus.     (Grandin  and  Jarman.) 


felt,  popularly  known  as  "quickening."  From  the  eighteenth  week 
up  to  the  end  of  pregnancy  the  foetal  heart-sounds  are  heard,  which 
vary  from  120  to  160  per  minute.  During  the  last  three  months  the 
uterus  becomes  more  distended,  its  walls  are  more  muscular  and  vas- 
cular. After  a  period  of  380  days  of  gestation  labor  begins,  and  the 
contents  of  the  uterus  are  expelled.  At  birth  the  ligature  of  the 
umbilical  cord  cuts  off  the  placental  circulation.  The  placenta, 
being  now  a  foreign  body  in  the  uterus,  is  expelled.  The  ruptured 
and  opened  vessels  of  the  uterus  are  closed  by  the  contraction  of  its 
walls,  and  haemorrhage  is  avoided.  The  mother  must  eliminate  dur- 
ing pregnancy  not  only  the  waste  of  her  own  organism,  but  also  that 
of  the  foetus.  Hence  the  kidneys,  being  overworked,  are  occasionally 
the  cause  of  urtemic  convulsions. 

Enlargement  of  Mammaey  Glands  in  Pregnancy. — Starling 
found  that  the  injections  of  a  part  of  the  dried  embryo  of  rabbits 


REPRODUCTION. 


789 


cause  an  onormons  enlargement  of  the  mammary  glands  of  the 
rabbit,  showing  that  the  sympathetic  enlargement  of  the  mammary 
glands  in  pregnancy  is  due  to  some  chemical  agent,  a  hormone,  act- 
ing through  the  blood,  and  not  by  the  nervous  system. 


Fig.  .S93.— The  Foetal  Circulation.     (Grandin  and  Jarman.) 


Placenta. — The  placenta  is  the  nutritive,  excretory,  and  respir- 
atory organ  of  the  foetus  from  the  third  month  to  the  end  of  preg- 
nancy. It  is  discoid  in  shape,  one  side  being  attached  to  the  uterine 
wall,  the  other  becoming  attenuated,  to  end  in  the  umbilical  cord, 
which  is  the  medium  of  exchange  between  the  placenta  and  the 
foetus.     The   villi   of    the    chorion    frondosum    dip    down    into    the 


790  PHYSIOLOGY. 

mucous  membrane  of  the  uterus,  to  push  against  the  walls  of  the 
large  vessels  found  there  and  whose  structure  is  similar  to  that  of 
capillaries.  The  cells  comprising  the  villi  act  as  an  osmotic  mem- 
brane through  which  osmosis  occurs.  By  this  means  oxygen  and 
nutritive  lymph  pass  from  the  mother's  blood  to  that  of  the  foetus. 
On  the  other  hand,  the  fffital  blood  gives  off  carbon  dioxide  and 
probably  urea.  There  is  no  intermingling  of  the  two  blood-currents, 
since  there  is  always  a  layer  of  epithelium  to  act  as  a  limiting  mem- 
brane. 

Fcetal  Circulation. — The  blood  is  brought  to  the  body  of  the 
foetus  by  the  umbilical  vein.  Some  of  this  oxygenated  blood  passes 
through  the  liver  to  the  hepatic  veins,  to  be  emptied  into  the  inferior 
vena  cava.  The  remainder  of  the  umbilical  blood  passes  into  the 
inferior  vena  cava  through  the  ductus  venosus. 

The  blood,  mixed  with  that  which  is  returned  from  the  lower 
extremities,  enters  the  right  auricle.  Guided  by  the  Eustachian 
valve,  it  passes  over  into  the  left  auricle  through  the  foramen  ovale. 
The  blood  now  courses  through  the  left  ventricle,  aorta,  the  hypo- 
gastric and  umbilical  arteries  to  the  placenta. 

The  blood  is  returned  from  the  head  and  the  upper  extremities 
to  the  right  auricle  by  the  superior  vena  cava.  This  stream  of  blood 
passes  through  the  auricle  and  auriculo-ventricular  opening  directly 
into  the  right  ventricle,  guided  by  the  tubercle  of  Lower.  The  blood 
next  passes  into  the  pulmonary  artery.  Some  of  it  (enough  to  nour- 
ish the  solid  lung-substance)  passes  to  the  lungs,  but  the  major  por- 
tion passes  into  the  aorta  through  the  ductus  arteriosus.  When  in 
the  aorta  it  takes  the  course  of  the  blood  from  the  left  ventricle  to 
finally  reach  the  placenta.  The  blood  to  the  lungs  returns  to  the 
left  auricle  through  the  pulmonary  veins. 

After  hirth  the  umbilical  arteries  are  obliterated  with  the  excep- 
tion of  their  lower  portions,  which  remain  as  the  superior  vesical 
arteries.  The  umbilical  vein  becomes  obliterated  and  remains  as  the 
round  ligament  of  the  liver.  The  umbilicals  become  impervious  soon 
after  cessation  of  the  placental  circulation. 

The  foramen  ovale  closes,  thereby  cutting  off  communication 
between  the  right  and  left  hearts.  By  the  second  or  third  day  the 
ductus  arteriosus  has  also  become  obliterated,  to  be  present  in  adult 
life  as  the  ligamentum  arteriosum. 

These  changes  in  the  circulatory  apparatus  are  dependent  upon 
the  establishment  of  pulmonary  respiration  at  birth.  The  first  in- 
spiration is  said  to  be  due  to  a  sensory  reflex  from  the  colder  air 


REPRODUCTION.  791 

striking  the  sensory  skin  filaments  of  the  chest  and  abdomen.  After 
the  cord  is  tied  there  soon  follows  an  increase  of  COo  in  the  blood. 
By  its  presence  the  activities  of  the  respiratory  center  of  the  medulla 
are  instigated.  However,  the  various  centers  are  but  feebly  irritable 
at  birth  and  require  somewhat  heroic  stimulation  to  bring  out  their 
activities.  This  feeblenetrs  accounts  for  the  remarkable  vitality  of 
the  infant  and  its  intense  resistance  to  asphyxiation. 

EVOLUTION.* 

All  modern  conceptions  of  the  immense  multiformity  in  the 
animated  world  are  based  upon  the  observed  facts  of  perpetuating 
established  forms  by  heredity  and  the  arising  of  new  forms  by  varia- 
tion. The  main  points  of  discussion  are  how,  when,  and  where  the 
physiological  phenomena  of  heredity  and  variation,  leading  ulti- 
mately to  evolution,  set  in.  While  the  discussion  of  these  problems 
has  been  going  on  for  centuries  past,  a  great  stimulus  for  approach- 
ing them  in  a  more  rational  way  has  been  given  by  Darwin  with  the 
publication  of  his  views  of  the  "Origin  of  Species."  Having  observed 
the  great  variety  of  forms  produced  by  breeders  of  animals  and  culti- 
vators of  plants,  through  artificial  selection,  he  was  led  to  assume 
that  the  natural  selection  has  been  the  cause  of  the  multiformity  of 
animals  and  plants  in  nature.  It  was  particularly  plausible  to  accept 
this  view  of  a  gradual  development  of  a  new  species,  if  there  was 
taken  into  consideration  the  needed  adaptation  to  dominating  cir- 
cumstances; the  constantly  taking  place  in  nature  of  the  struggle 
for  existence,  with  its  consequence  of  the  survival  of  the  fittest;  and 
last,  but  not  least,  the  transmission  of  the  changes  acquired  through 
the  mentioned  factors  to  succeeding  generations  by  heredity.  It  is 
evident  that  Darwun  based  his  views  only  upon  facts  available  at  that 
time  and  known  from  observations  of  adult  forms,  but  these  facts 
alone  could  not  be  considered  as  sufficient  evidence  for  his  views. 
The  theory  itself,  however,  was  so  fascinating  that  a  great  num- 
ber of  enthusiastic  investigators  were  induced  to  study  the  de- 
velopment of  individual  animals,  and  the  facts  revealed  by  embryo- 
logists  at  that  period  have  been  astonishing.  It  has  been  shown  that 
all  metazoa  develop  from  ova,  that  the  ova  of  all  animals  undergo  a 
similar  process  of  segmentation,  and  in  every  case  a  blastoderm  is 
formed,  first  consisting  of  a  single  layer,  but  consecutively  changing 
into  one   of   two,   and    finally   one    of   three   layers   of    cells.     The 


*  Contributed  bv  Dr.  P.  Fischelis. 


792  PHYSIOLOGY. 

similarity  between  those  early  stages  in  tlie  development  of  widely 
dill'erent  animals  has  been  i'ound  to  be  so  striking  that  it  is  impos- 
sible to  distinguish  one  animal  From  another  at  this  stage,  and  these 
I'aets  gave  rise  to  the  Uadnvii  tneory  ol  llaeckel  in  support  of  the 
views  of  Darwin.     llaeckel  considers  that  all  forms  of  blastoderms, 
consisting  of  two  germinal  layers,  can  be  looked  upon  as  modifica- 
tions of  the  simple  gastrula;   and  as  a  gastrula  is  the  foundation  for 
the  development  of  a  single  individual — ontogenesis — so  a  simply  con- 
structed animal  similar  to  it  is  to  be  considered  as  the  ancestor  of 
all  metazoa.     He  even  constructed  a  treelike  diagram  to  illustrate 
how,  from  an  undifferentiated  being,  gastrcm,  by  means  of  the  above- 
mentioned  factors  pointed  out  by  Darwin,  an  evolution  to  different 
types,  varieties,  and  species — phylogenesis — observed  in  the  animal 
world,  could  take  place.     Haeckel  has  published  his  views  not  only 
for  scientific  readers,  but,  through  his  popular  publication,  he,  more 
than  any  one  else,  made  the  discussion  of  the  problems  of  evolution 
and  inheritance  accessible  to  the  public  at  large;   and  the  literature, 
scientific  as  well  as  unscientific,  called  forth  by  his  efforts,  for  and 
against  this  theory,  is  enormous.     The  scientific  investigations,  how- 
ever, have  failed  to  show  as  yet  a  single  instance  of  a  gastrula,  or 
its  modification,  developing  into  any  other  animal  than  one  similar 
to  that  from  which  it  itself  originated.     On  the  other  hand,  it  has 
been  conclusively  shown  that  the  physiological  differentiation  of  the 
cells  constitutnig  the  blastoderm  is  established  long  before  the  germ- 
inal layers  are  distinctly  differentiated.     We  must,  therefore,  con- 
clude that  the  lever  for  lifting  the  mystery  of  our  phenomena  is  to 
be  applied  at  an  earlier  period  than  the  already  formed  blastoderm. 
The  facts,  which  have  accumulated  within  recent  years,  on  the  mor- 
phology of  the  cell  and  its  physiological  manifestations  during  the 
process  of  reproduction  have,  as  we  have  seen  above,  been  astonish- 
ing.    Particularly  the  nucleus  has  attracted  the  most  attention,  and 
it  has  been  shown  very  conclusively  that  the  chromosomes  of  the 
nuclei  of  the  sexual  cells  are  the  principal  factors  in  transmitting 
the  hereditary  manifestations  during  reproduction.     The  most  recent 
studies,  particularly  those  of  Conklin,  have  revealed  the  fact,  how- 
ever, that  the  cytoplasm  of  the  egg-cell  also  has  a  more  highly  dif- 
ferentiated structure  than  was  suspected.     It  has  been  conclusively 
shown  that  many  of  the  future  organs  are  already  mapped  out  in  the 
two-cell  stage,  and  even  in  the  unsegmentated  ovum. 

It  was  only  natural  that  these  new  discoveries  should  exercise 
great  influence  upon  the  conception  of  evolution,  and  therefore  a 


REPRODUCTION.  793 

new  theory,  embod3'ing  all  the  newest  achievements,  could  be  expected 
to  be  received  with  favor.  This  new  theory  is  suggested  by  De  Vries 
as  the  "mutation  theory,"  and  is  founded  upon  the  phenomena  of  the 
cell-life.  It  is  a  theory  of  evolution  of  living  organisms  through 
evolution  of  their  germ-cells,  and  suggests,  in  the  words  of  Conkliu, 
that  similarities  in  the  character  and  localization  of  the  material  sub- 
stances of  the  egg  must  be  the  initial  causes  of  all  similarities  or 
homologies  which  appear  in  the  course  of  development.  Modifica- 
tions of  this  germinal  organization,  however  produced,  are  probably 
the  immediate  causes  of  evolution;  and  if  it  is  to  be  accepted  as 
probable  that  certain  types  of  animals  have  been  derived  from  others, 
it  is  evident  that  such  transformations  might  be  accomplished  far 
more  easily  in  the  egg  than  in  the  adult.  Relatively  slight  modifica- 
tions in  the  germinal  organization  would  convert  one  type  into 
another. 

We  find  here  the  question  raised,  whether  sudden  alterations  of 
germinal  organization  may  not  lie  at  the  basis  of  the  origin  of  new 
types. 

How  much  nearer  this  new  theory  will  bring  us  to  the  proper 
conception  of  the  physiological  "phenomenon  of  life"  itself  and  the 
"phenomenon  of  reproduction"  of  living  beings,  as  a  manifestation 
of  the  preservation  of  energy  underlying  the  former,  remains  to  be 
seen.  The  solution  of  the  ultimate  and  most  mysterious  of  all 
problems — the  question  of  the  "origin  of  life" — seems  to  be  as  remote 
as  ever. 

LiTEBATUBK   CONSULTED. 

Heisler's  "Embryology." 

Boveri,  "Das  Problem  der  Befruchtung,"  1902. 


UNITS  OF  MEASUREMENT. 


French  Measures  of  Length,  Weight,  and  Volume. 

1  millimeter  =  Vij,  centimeter  =  Viooo  meter. 
1  centimeter  =^  ^/mo  meter. 
1  micromillimeter  (1  /a)  =  Viooo  millimeter. 
1  liter  =  1000  centimeters  cubes  (1000  c.c). 

Relation  hettveen  Volume  and  Weight. 

1  c.c.  =  1  gramme. 
1  milligramme  =  Vioon   gramme. 
1  kilogramme  =  1000  grammes. 

Length.     French  to  English. 

1  centimeter  =    0.39371         inch. 

1  meter  =39.37079         inches. 

1  micromillimeter  =    0.00003937  inch. 

{To  convert  centimeters  into  inches  multiply  by  ^'Vas-) 


Weight.     English  to  French. 

1  grain  =        0.0648  gramme. 

1  ounce  =      28.3495  grammes. 

1  pound  =    453.592 

1  stone   =        6.35  kilogrammes. 

1  ewt.     =      50.8 

1  ton      =1016  " 


Weight.     Fren-ch  to  English. 

1  gramme  =  15.432349  grains. 

1  kilogramme  =  2.2046213   pounds, 

or  about  35  ounces. 
1  milligramme  =    0.015432  grain. 
(794) 


UNITS  OF  MEASUREMENT.  795 

Volume.     English  to  French. 

1  cubic  inch  =    16.3861759  centimeters  cubes. 

1  fluid  ounce  =    28.3495 

1  pint  =567 

1  cubic  foot  =    28.3153  liters. 

Volume.     French  to  English. 

1  centimeter  cube  =    0.061027  cubic  inch. 

1  liter  (1000  c.c.)  =61.027  cubic  inches, 

or  35  fluid  ounces, 

or  1^/4  pints. 
1  meter  cube  (1000  liters)  =  35.3  cubic  feet. 

Measures  of  Energy. 

1  kilogrammeter  =  about  7.2-4  foot-pounds. 
1  foot-pound        =      "      0.1381  KgM. 

Mechanical  Equivalent  of  Heat. 
1  kilocalorie  =  424   (or  423.985)   kilogrammeters. 

Fahrenheit  and  Centigrade  Scales. 

To  convert  Fahrenheit  into  Centigrade  subtract  32  and 
multiply  by  Vo- 

To  convert  Centigrade  into  Fahrenheit  multiply  by  ^/., 
and  add  32. 


i:n^dex. 


Abdominal  reflex,  607 
Abducent  nerve,   755 
distribution,   755 
function,  755 
origin,    755 
pathology,    755 
physiology,   755 
Aberration,   722 
chromatic,   722 
spherical,  722 
Absorption,   130 
by  the  skin  and  lungs,  158 
by  blood  vessels,  157 
from  intestines,  138 
stomach,  138 
within,    130 
without,  130 
of  alcohol,  138 
carbohydrates,  139 
fats,  141 
proteids,  140 
salts,  138,  139 
water,   138,   139 
rapidity  of,   142 
time  of,  143 
Accessory  foods,   13 
Accessory  nucleus  dentatus,  614 
Acid   sodium   urate,   399 
Acid  fermentation  of  urine,   407 
Acid  poisoning,  429 
Accommodation  of  the  eye,  722 
act  of,  722 
defects   of,   722 
for  distance,  724 
mechanism  of,  723 
Acetic  acid  fermentation,  124 
Acetonaemia,   120 

Achromatic  nuclear  substance,  12 
Achroodextrin,  62 
Acids  in  the  gastric  juice,  71 
Acromegaly,   372 
Adam's  apple,  493 
Adaptation,   791 
Addison's  disease,  367 
Adenin,   371 
Adipocere,   472 

Adrenalin,   291,   354,   367,  369,   645,   709 
Adrenal  glands,  365 
blood  supply  of,  367 
choline  secretion,  365 
extract  of,   369 
function  of,  367 
results  of  extirpation   of,   367 
secretory  nerves  of,  370 
structure  of,  366 
Aeroplethysmograph,   320 
iEsthesiometer,   660 
Afferent  impulses  of  cerebellum,  620 
After-images,    737 
Age,   influence  on  capacity  of  respiration, 

321 
Agglutinins,  293 
Agraphia.  502 
Aim  of  alimentation,  421 
Air,    351 
complemental,  319 
compressed,  352 
quantity  breathed,  319 
rarefied,  353 
reserved,  319 
residual,  319 
tidal,  319 
vital  capacity  of,  319 


Air  cells,  306 

Air  passages,  302 

Air  tubes  (see  bronchi). 

Ala  cinerea,  556,  567 

Alanin,   33 

Albumin,  34 

alkali,   34 

acid,  34 

derived,  34 

egg,  34 

in  urine,  321 

native,  34 

serum,   34 
Albuminuria.  411 

causes,  411 

tests,  411 
Albuminates,  34 
Albuminoids,  36 
Albumoses,  81,   93 
Albumosuria,  410 
Alcohol,  43 

heat  value  of,  431 
Alcoholic  fermentation,  124 
Aleuron  granules,  34 
Alexia,  501 
Alimentary  canal,  46 
length,  46 

parts  of,  46 

substances,  24,  37 
Alkali  albumin.  34 
Alternate  hemiplegia,  621 
Alteration  theory  of  nerve  currents,  523 
Alveolus,  50 

Amido  acids,  32,  35,  103,  104 
Ammonia,  32,  120,  402 
Ammonium  carbonate,  397 

magnesium  phosphate,   410 
Amnion,  783 
Amtuba.   9,   15 
Amoeboid  movement,   15 
Amphipyrenin,  13 
Ampulla,  508 
Amyloses  or  starches,  28 

action  of  saliva  upon,  60,  62 
pancreatic  juice,  100 
Amylopsin,   100 
Amyloses,   28,  29 
Anabolic  processes,  420 
Anatomy,  3 
Animal  heat,  436 

estimation  of,  438,  441 
extremes  of  temperature,  440 
post-mortem  rises,  455 
Animals,  437 

cold  blooded,  437 

temperature  of,  437 

warm  blooded,  437 
Anions,   131,   132 
Ankle  clonus,  607 
Anosmia,  675 
Anospinal  center,  127 
Anterior  columns,  539,  545 

root  fibers,  545 

pyramids,  553 
Antero-lateral   ascending  cerebellar  tract, 

547 
Antero-lateral  ground  bundle,  545 
Antiferments,  82 
Antipepsin,  71,  82 
Antiperistalsis,  91 

Antiseptic  action  of  hydrochloric  acid,  82 
Antitoxins,  292 
Anus,  90 


(797) 


798 


INDEX. 


Aphasia,  501 
Aphemla,  502 
Aphonia,  500 
ApnoDa,  333 

Aqueductus  Sylvius,  567 
Aqueous  humor,  716,  722 
Arachnoid,  537 
Aromatic  amino  acids,  32 
Arcuate  fibers,  560 
superficial,  560 
deep,  5C0 
Areas  of  Cohnheim,  461 
Arginine,  32,  103,  104,  129,  397 
Argyll-Robertson   pupil,   746 
Arterial  blood,  161,  163 
Arteries  (see  names  of),  246 

bronchial,  307 

coats  of,  197,  247 

contractility  of,  255 

coronary,  225 

elasticity  of,   253 

lymph  spaces  of,  148 

muscularity  of,  247 

nerve  supply  of,  247 

pressure  of  blood  in  asphyxia,  335 

pulmonary,  204 

pulse,   255 

rate  of  movement  of  blood  in,  275 

structure,  247 

tension,  271 

vasa  vasorum,  247 
Artery  of  cerebral  haemorrhage,  587 
Articulate  sounds,   classification  of,   499 

vowels  and  consonants,  499 
Artificial  respiration,  336,  337 
Laborde  method,  338 
Marshall   Hall  method,  337 
Ploman's  experiments,   337 
Shafer  method,  337 
Sylvester  method,  336 
Arytenoid   cartilages,  493 
Arytenoideus  muscle,   495 
Ascending  loop  of  Henle,  389 
Ase,  60 

Aspartic  acid,  32,  103 
Asphyxia,  335 

artificial  respiration  in,  336 

causes  of  death  in,  336 

effect  upon  circulation,  335 

stages  of,  335 
Aspiration  of  heart  and  thorax,  279 
Association  areas  of  Flechsig,  631 
Aster,   21 
Astigmatism,  726 
Atmospheric  air  (see  air). 

pressure  in  relation  to  respiration,  351 
Atoms,  5 

Atropine,  effects  of, 
on  heart,  242 
lacrymal  gland,  742 
respiration,  327 
salivary  glands,  63 
Auditory  area,  626 

auricle,   678 

cells,  684 
external,  685 
internal,  684 

center.  626 

field,  679 

judgment,  696 

nerve,  685 

sounds,   696 

striae,  565 
Auerbach's  plexus,  68,  91 
Auricle  of  ear,  677 
Auricles  of  heart,  210 

diastole  of,  213 

systole  of,  213 
Auriculo-ventricular     valves     (see     heart 
valves). 


Automaton,  632 
Avogadro-Van't  Ho£E  law,  134 
Axis  cylinder,  529 

Bacillus  coli  communis,  61,  124 
Bacteria,   classification  of,   122 

digestion  by,  123 

fermentation  by,   124 

in  intestines,  124 
Balance  of  nutritional  exchange,   422 
Basophiles,  171 

Beckman's  differential  thermometer,  135 
Beef  tea,  39 

Beef  toxic  principles,  39 
Beer,  43 
Bell's  law,  60? 

apparent  contradiction,  604 
palsy,  763 
Bernard's  puncture,  119 
Betatetrahydronaphthylamin,  448 
Bethe's   theory   of   nerve-cell   connections, 

528 
Bicuspid  valve,  207 
Bicycle  heart,  239 
Bidder's  ganglion,  232 
Bile,  109 

acids  of,   110 

action  of  drugs  on,  121 

action  on  muscles  and  nerves,  115 

antiseptic  powers  of,  115 

capillaries,   106 

cholesterin,  113 

composition  of,  110 

derivatives  of  salts  and  pigments,  111 

ducts,  106 

mucin,   110 

pigments.    111 
in  urine,  406 

properties  and  constituents  of,  108,  110 

quantity  secreted,  109 

reabsorption  of  salts,   116 

salts,   110 

specific  gravity,   109 

tests   for,   Gmelin's,   112 
Hay's,   111 
Pettenkofer's,   111 

uses  of,   114 
Bilirubin,   112 
Biliverdin,    112 
Binaural  audition,  695 
Biology,  2 
Biuret  test,  35 
Bladder,  417 
Blastoderm,  772 
Blind  spot,  728 
Blood,  160,  161 

arterial,  161 

buffy  coat,   194 

carbon  dioxide  in,  191,  350 

cause  of  movement  of,  212,  253 

circulation  of,  211,  249 
schema,  251 

coagulation  of,   191 

color  of,  160 

composition,   180 

crystals,  179,  181 

distribution  of,  162 

difference   between  arterial   and  venous, 
163 

experiments  upon,   169 

fibrin  of,   191 

function    of,    160 

globucidal  action  of,  197 

gases  of,   191,   343,  344 

htpmoglobin,  179 

laking,   169 

medico-legal   tests,   199 

odor,  162 

oxygen  in,   165 

pigments  in  urine,  406 


INDEX. 


799 


Blood,  plasma,  1S9 

plates  of,  175 
proteids  of,   189 
quantity  of,  162 
reaction,    161 
renewal  of,  166,  196 
serum,   192 
specific  gravity,  161 
spectra,  186 
taste,  161 

temperature  of,  161 
estimation  of,  162 
transfusion,  197 
volume  of,  189 

Welcker's   estimation,    162 
venous,  163 
Blood-corpuscles,  163 
blood-platelets,    175 
chemical  composition  of,  180 
chemistry  of,   179 
count   of,    167,   168 
destruction  of,  166 
diapedesis  of,  174 
experiments  upon,  169 
of  different  animals,   163 
parasites,   166 
vitality  of,  170 
red-corpuscles,   action  of  inorganic  sub- 
stances, 169,  170 
destruction  of,   167 
formation  of,  176 
in   extra-uterine   life,   177 
in  intra-uterine  life,  176 
function  of,   165 
life  cycle  of,   166 
methods  of  counting,   167 
number,   166 

conditions  affecting,  166 
parasites,   166 
place  of  destruction,  171 
rouleaux,   165 
shape,  164 
size,  164 
white  corpuscles,   170 
amteboid  movements  of,   172 
disappear  when  blood  is  drawn,  171 
function   of,   173 
number  of,  171 
origin  of,  174 
structure  of,  170 
variations   in   number,   171 
varieties,  171,   172 
where  found,  171 
Blood-crystals,  178 
Blood-platelets,  175 
Blood-pressure,  263 

effect  of  vagus  on,  234,  272 
extremes  of,  271 
in  man,  271 

measurement  of,  269,  270 
pathological,  273 
respiratory  wave,  269,  272 

causes,    272 
Traube-Hering  curve  of,  272 
variations  of,   272 
venous,   273 
Blood-vessels,  252 
circulation  in,  252 
Weber's   schema,    25J 
Body,   chemical  constituents  of,   25 
Bowditch   stair-ease  contraction,  244 
Body  cavity,  6 
Bony  labyrinth,  681 
Bowman's  capsule,   388 
Boyle-Van't  Hoff  law,  134 
Boveri   on   fertilization,   777 
Brain  (see  cerebellum,  pons,  etc.). 
action  of  extracts  of,   634 
aqueduct  of  Sylvius,   567 
artery  of  hamorrhage,  587 


Brain,  blood-supply  of,  586 

circulation  in,  586 

claustrum,  581 

corpora  quadrigemina,  582,  622 

corpora  striata,  578,  623 

external  form,   570 

extirpation  of,  623 

fissures  of,   570 

fourth  ventricle,  566 

ganglia  of,  578 

gray  matter  of,  576 

internal  capsule,   582 

lobes,  573 

motor  areas,  625 

optic  thalamus,  578,  623 

sensory   areas,   625 

structure  of  convolutions  of,   577 

tracts,    cortico-pontal    cerebellar,    584 
motor,   584 
sensory,  586 

white  matter,  578 
Bread,   33 
Bread  juice,  comparative  value  of,  75,  95, 

96 
Breathing   (see   respiration). 
Bromelin,   100 
Bronchial  system,  305 
Bronchi,  307 

blood-supply   of,   307 

unstriped  muscle,  327 
Brunner's  glands,  89 
Buffy  coat,  194 
Bulb   (see  medulla). 
Bulbar  nerves,  610 
Burdach's  column,  549 
Butter,  42 
Buttermilk,  42 
Butyric  fermentation,  124 

Cachexia  strumipriva,  361 

Cfecum,  60 

Caffeine,   44 

Caissons  and  effect  of  compressed  air,  351 

Caisson  paralysis,  351 

Calamus  scriptorius,  555 

Calcium  carbonate,   410 

oxalate,  401 

phosphate,  406 
Calorie,  431 
Calorimeter,  442 
Calyces  of  kidney,  387 
Camera  obscura,  721 
Canal,  alimentary,  46 

external   auditory,   678 
function,  679 

Petit's.  716 

Schlemm's,  703 

Stilling's,  716 

semi-circular  of  ear,  696 
Cannon's  experiments  on  stomach,  69 
Capacity  of  chest,  vital,  319 
Capillaries,   248 

anatomy  of,  248 

bile,  107 

blood-pressure  in,  273 

capacity,  249 

circulation  in,  259,  261 

histology,    248 

passage  of  corpuscles  through  walls,  174 

rate  of  blood  in,  276 

size.   248 
Capillary  circulation,  259 

blood-pressure,  273 

swiftness,   276 
Capsule  of  Bowman,  388 
Capsule  of  Glisson,  106 
Capsule  of  Tenon,  618 
Carbamid,  Z9b 
Carbohydrates,  27,  38 

absorption  of,  139 


800 


INDEX. 


Carbohydrates,  heat  value  of,  431 

in  metabolism,  427 
Carboluria,   406 
Carbon  equilibrium,  424 

estimation  of,  427 
Carbon  monoxide,  351 
Carbon  monoxide  haemoglobin,  183 
Carbonic  acid,  351 
in  blood,  191,  349 
in  urine,  407 
Cardiac  glands,  68,  71 

impulse,  216 

mucous  membrane,  72 

pathology,  290 

revolution,   213 

sphincter  in  vomiting,  83 

sympathetic,  241 
Cardinal  points  of  Gauss,  720 
Cardiograms,  217 
Cardiographs,  216 

Sanderson's,   216 
Cartilages  of  larynx,   492 
Caseanic  acid,  41,  104 
Casein    (see  milk),   41 
Caseinogen,  41,  101 
Catabolic  processes,  420 
Cataract,  710 
Cathions,  131 
Cauda  equina,  537 
Caudate  nucleus,  579 
Cell-division,  17 
direct,  19 

endogenous   nuclear   multiplication,   22 
indirect,  20 
Cells.  1,  7 

achromatin,   12 

afferent,  583 

animal  and  vegetable,  differences,  5 

blood   (see  blood-corpuscles). 

ciliated,  15 

constituents,    7 

definition,   7 

Deiters's,  621 

efferent,  533 

fatigue  of,   23 

gustatory,    677 

Langerhans's,   95,   102 

nerve,  524 

Nissl  granules,  527 

nuclear  sap,  12 

nucleolus,  13 

nucleus,  12 

olfactory,   672 

oxyntic,  68 

parietal,  68 

parts  of,  7 

Purkinje's,  617 

selective  power  of,   24,   130 

tactile,  656 

theory  of,  5 

vegetable,  6 

wall,  8 
Cellulipetal   fibers,  533 
Cellulifugal   fibers,   533 
Cement,   53 
Center  of  smell,  626 
Central  nucleus,  564 
Centrosome,  13,  21 

definition,  13 

division   of,   14 

number,  14 

size,  14 

staining  of,  14 
Cereals,  43 
Cerebellum,  612 

accessory  nucleus  dentatus,  614 

afferent  impulses,  620 

arbor  vitse,  614 

center  of   coordination,   620 

corpus  dentatum,  614 


Cerebellum,  cortex,  structure  of,  615 
efferent  impulses,  620 
experiments  on,   619 
function  of,   620 
general  description,  613 
internal  structure,  615 
nuclei  of,  614 
median    lobe,   613 
peduncles,   621 
Purkinje  cells,  615 
section  of,  621 
spinal  cord  connections,  617 
surface  form,  613 
valley   of,   613 
Cerebral  convolutions,  structure  of,  577 
Cerebral   cortex,   577 
ablation,  63^; 

action  of  brain-extracts  on,  634 
motor  centers,   625 
sensory  centers,  626 
Cerebral   detrusor   center,   418 
Cerebral  hemispheres,  experimental  phys- 
iology of,  632 
effect  of   destruction,   632 
irritability   of   cortex,   634 
Cerebral  peduncles,  564 
crusta,  565 
locus  niger,  565 
tegmentum,   566 
texture,   565 
Cerebrins,  535 
Cerebrospinal   fluid,    637 
action  of  drugs  on,  638 
composition,   637 
differences  from  plasma,  637 
origin,   637 
Cerebrum    (see   brain). 
Cerumen,   678 
Chambers  of  eye,  716 
Champagne,   44 

Charcot's  artery  of  hsemorrhage,  587 
Cheirokinesthetic  center,   501 
Chemical  composition  of  the  body,  25 
Chemiotaxis,   16 
Chest  in  respiration,  313 

voice,  491 
Cheyne-Stokes  respiration,   340 
Chlorides  in   urine,  406 
Chlorophyll,  183 
Chlolagogues,   121 

Chloroform  on  electrical  responses,  522 
Cholesterin,   112,    113 
Cholin,   113,   366,   637 
Chorda  tendineae  (see  heart). 
Chorda  tympani,   63 
Chorion,  783 

Chorium  frondosum,  783 
Choroid  coat  of  eye,  703 
Chromatic  aberration,   722 
Chromatic  nuclear  substance,  12 
Chromatolysis,  527 
Chromogen,   366 
Chromosomes,   21 
Chyle,   153 
coagulation  of,   153 
composition,  153 
corpuscles,   153 
flow,  153 
quantity,  157 
Chyme,  83,  85,  115 
Cilia,  15 

Ciliary  movement,  15 
body,   707 
ganglion,  759 
muscles,  706 
processes,  705 
system,  717 
Cilio-spinal  center,  609 
Circles  of  diffusion,  72 


INDEX. 


801 


Circulation,  201,  211,  215 

actiou  of  heart  in,   215 

capillary,   259 

comparative,  202 

course  of,  211 

early  discoveries,  249 

in  blood-vessels,  252 

•  brain,  279 
frog's  foot,  250 
lower  animals,  202 
portal  system,  106,  211 
pulmonary  system,  211 
renal  system,   391 
systemic  system,  211 
venous  system,   277 

influence  of  asphyxia,  335 

pathological  conditions  of,  215,   220 

of  blood,  249,  215 

duration,   277 

rapidity,  273 
Circulatory  system,  211 
Circumvallate  papilla,  666 
Clarke's  column,  543 
Claudius's  cells,  685 
Claustrum,   581 
Clava,  555 
Climacteric,  786 
Coagulation  of  blood,   191 

conditions  affecting,  195 

factors  of,  195 

of  milk,   41 

process  of,   tabulated,   193 

rapidity,  191 

theories   of,    192 

why  it  does  not  in  vessels,  195 
Coagulases,  61 
Cocoa,  44 
Cochlea,   682 
Cochlear  nerve,   685 
Coffee,  44 
Coffeon,  44 

Cohesion  of  nerves,  535 
Cohnheim's  areas,  461 
Cold-blooded  animals,   437 
Cold  spots,  661 
Colloids,   137 
Colon,  89,  90 
Colon  bacillus,  124 
Color-vision,  733 

blindness,   735 

phenomena  of  perception,  734 

sensations,  734 
Colostrum,  40,   376 

corpuscles,  42 
Comma-tract,  549 
Commissures  of  cord,   550 
Complemeutal   air,   319 
Complementary  colors,  735 
Compounds,  25 

inorganic,   25,   26 

organic,  25,  26 
Compressed  air  of  caisson,   352 
Cones,   712 

Conjugate   deviation,   537 
Conjugated  sulphates,   120,  407 
Conjunctiva,   701 
Conklin's  discoveries,  792 
Connective-tissue   spaces.   148 
Contractility  of  muscle,   467 
Contraction  of  pupil,  709 
Convolutions  of  brain,   573 
Cord,    spinal    (see   spinal   cord). 
Corium,  655 
Cornea,  701 
Coronary  arteries,  225 
Corona  radiata,  582 
Corpora  quadragemina,  582,  622 
Corpora  striata,  578,  623 
Corpus  callosum,   570 
Corpus  dentatum,  614 


Corpus  luteum,  787 

of  menstruation,   787 

of  pregnancy,  787 

spongiosum,  784 
Corpus  striatum,   578,  623 
Corpuscles    (see   names   of). 
Corti  arches,   684 

canal,  684 

membrane,  685 

organ  of,  684 
Cortical   epilepsy,  628 
Cortico-pontal-cerebellar   tract,   565,   584 
Coughing,   339 
Cranial  ganglia,  578 
Cranial  nerves,  748 
decussations,    748 
origin.  750 

spinal  nerves,  comparison  with,  749 
Creatinin,  402 
Cremasteric  reflex,  608 
Cresol,  120,  124 
Cretinism,  361 

Crico-arytenoid  muscle,  495 
Cricoid  cartilage,  492 
Crista  acousticce,  555 
Crossed  pyramidal  tract,  547 
Crusta  petrosa,  53 
Crowbar  case,  633 
Cruciate  centers,  449 
Crusta,  565 
Cryoscopy,    135 
Crystalline   lens,   709 
Crystalloids,  137 
Cuneate  nucleus,  556,  560 
Cuneus,    627 
Cupola,  682 
Curdling  ferments,  67 
Currents,  nerve,  521 
Cutis  vera,   655 
Cytotoxins,  294 
Cystic  duct,  108 
Cystine,  32,   410 

Daltonism,  735 
Darwin  on  evolution,  791 
Descemet's  membrane,  702 
Decidua  reflexa,  780 
Decidua  serotina,  7S0 
Defecation,  126 

center,  127 

mechanism  of,  127 
Degeneration  of  nerves,  604 
Deglutition,  57,  58 

of  fluids,  58 

of  solids,  57 

(see   swallowing.) 
Dehydration,  421 
Deiters's  process,  528 

nucleus,  621 
Daland's  hsematocrit,   169 
Demodex  foUiculorum,  662 
Dendrons,  528 
Depressor  nerve,  238 
Dermis,  655 

Descending  tubule  of  Henle,  389 
Development  and  growth,   432 
Devries's  mutation  theory,   793 
Dextrins,  29 

erythrodextrin,  29 

achroodextrin,  29 
Dextrose  in  urine,  412 
Diabetes,   118,   404 

adrenalin,   119,  369 

experimental,   119 

inhalation,  120 

irritation   of  vagus   and   depressor,    120 

pancreatic,   101 

phloridzin,   119 

section  of  cord,  120 
Diabetic  puncture,  119 


802 


INDEX. 


D'Jelitzin's  artificial  respiration,  338 

Diamino  acids,   32,   103 

Diapadcsis,  174 

Diaphragm  in  respiration,  312 

Diaster,  22 

Diastase,  29,  118 

Diastole  of  heart,  215 

Dibasic  acids,  103 

Dicrotic  wave,  258 

Diet,  431 

Chittenden's  experiments,   431 

energy  table.  Hall,  431 
Atwater,  431 
Diffusion,  132 
Digestion,  24,  45 

changes  in  the  mouth,  60,  62 

divisions  of,   47 

gastric,  65 

intestinal,  85,  121 

in  large  intestines,  122 

mechanism  of,  79,  124 
Dioptrics,  721 

Diphtheria  toxin    (immunity),   291 
Diplopia,  738 
Direct  cell-division,  19 
Direct  cerebellar  tract,  547 
Direct  pyramidal  tract,  545 
Discus  proligerus,  775 
Double  vision,  738 
Doyere's  eminence,  464 
Dropsy,  138 

Drug  pigments  in  urine,  406 
Dubois-Reymond  coil,   510 
Ductless  glands   (see  names  of). 
Ductus  arteriosus,  790 
Ductus  cochlearis,   683 
Ductus  communis  choledichus,   108 
Duodenum,  85 
Duplication,  421 
Dura  mater,  537 
Dynamometer,  486 

Ear,  677 

anatomy,  677 

bones,   680 

description,  677 

external,  678 
function,  678 

internal,  681 
function,    694 

middle,  679 
transmission  by  air  of,  689 
transmission   in,    689 
Ectoderm,  5,  11 
Eck's  fistula,  397 

Efferent  fibers'  of  sympathetic,  639 
Eggs,  39 

Ehrlich's  theory   of  immunity,   292 
Ejaculation,   562 
Elastin,   37 
Elasticity,   484 

Electrodes,  non-polarizable,  507 
Electrolytes,   130 
Electrometer,  517 
Electrophysiology,  503 

Dubois-Reymond   coil,   511 

electrical      phenomena      of      contracting 
muscle,   519 

negative     variation     of     nerve-currents, 
521 

nerve-muscle  preparation,  516 

physiological  rheoscope,  516 
Electrotonic  variations,   598 
Electromotivity,  515,  596 
Electrotonus,   594 

Loeb's  theory  of,  596 

phenomena,   1 
Elements,  5 

in  body,  25 
Embryology,   773 


Emetics,  84 

Emmentia  teres,  567 

Emmetropic  eye,  724 

Emulsification,  30 

Enamel,  53 

Eud-bulbs,  657 

Endocardiac  pressure,  218 

Endocardium,   208 

Endogenous   nuclear  multiplication,  22 

Endolymph,  693 

Endomysium,  457 

Endoneurium,   532 

Energy,  434 

kinetic,  434 

potential,  435 
Enterokinase,  121 
Entoderm,   772,  782 
Enuresis,  608    ' 
Enzymes,   61 

classification  of,   61 

hydrolytic  action  of,  61,  103 
Eosinophiles,   171 
Epiblast,  782 
Epidermis,  653 
Epigastric  reflex,  607 
Epiglottis,   493 
Epineurium,  531 
Epimysium,  457 
Erection,  784 
Ergograph,  487 
Erepsin,  121 
Erythroblasts,  177 
Erythrodextriu,   29,   62 
Esophoria,  739 

Ether  on  electrical  responses,  522 
Eustachian  tube,  690 
Evolution,   791 

Exercise,   effect  on  temperature,   439 
Exophoria,   739 
Expiration,  314 

center,  333 

complex,  314 

effect  on  blood-movement,  324 

movements  of,  314 

muscles  of,  314 

simple,  314 
External  auditory  meatus,  677 

capsule,  581 
Eye,  700 

accommodation   for  distance,   724 

after-images,  737 

blood-vessels,  703,  716 

coats,  700 

co-ordinated   movements,   737 

general   description,   700 

imperfections  and  corrections,  725 

lymphatics,  718 

measurements,  719,  720 

movements,  740 

muscles,  740 

nerves,  708 

phosphenes,  713 

structure,  700 

Facial,  nerve,  762 
Bell's  palsy,  763 
chorda  tympani,  762 
distribution,  '763 
function,   763 
origin,  762 
pathology,   763 
physiology,  763 
Faeces,  125 
amount,  125 
color,  126 

composition,  125,  126 
variations,  125 
Falsetto  voice,  499 
Fasciculi,  457 
Fasting,  425 


INDEX. 


803 


Fatigue  of  cells,  23 
Fats,  29,  42 

absorption,   141 

composition,  29,  30 

heat  value,  430 

human  fat,  30 

in  metabolism,  426 

olein,  30 

origin,  30,  426 

palmatin,  29,  30 

stearin,  30 
Fauces,  49 
Feehner's  law,  653 
Fchling's  test,   422 
Female  pronucleus,  777 
Fenestra  ovale,  680 

rotundrum,  680 
Ferments      (see     blood,      milk,      digestive 
juices),  60 

definition   of,   61 
Fermentation,  124 

acetic,  124 

alcoholic,  124 

butyric,  124 

lactic,  41,  124 

oxalic,  124 

test  for  sugar,  413 
Fertilization,  797 
Fever,  454 
Fibers,  muscular,  458 

length  of,  458 
Fibrin,  191 
Fibrin  ferment,  193 
Fibrinogen,   36,   193 

Fifth   cranial   nerve    (see   trigeminus). 
Filiform  papillffi,  666 
Fillets.  568 
Filtration,   155 

theory  of  lymph,  155 
Filum  terminale,  536 
Fistula,  gastric,  79 

Flechsig's   association    areas,    629,    631 
frontal,  631 

parieto-occipito  frontal,  631 
insular,  631 
Flour,  wheat  as  a  food,  43 
F(T?tal  circulation,  790 
Foods,   42,   43 

accessory,  43 

caloric  value,  431 

chemical  constituents,  26 

daily  amount,  38 

definition,  24,  421 

vegetable,  42 
Formatio  reticularis,  557 
Fourth  cranial  nerve  (sec  trochlear). 
Fourth  ventricle,  561,  566 

boundaries,  561 

floor,  561 
Fovea  centralis,  714 
Fovea  hemielliptica,  682 
Fovea  hemispherica,  682 
Fovea  posterior,  567 
Fraunhofer's  lines,  185 
Freezing  point,   135 
Function,  4 

Fungiform  papillas,  666 
Funiculus  cuneatus,  556 

gracilis,  556 

teres,  567 

Gall-bladder,  108 
Galvanometer,  516 
Ganglia  of  heart,  232 
Gases  of  intestines,   124 
Gastrasa  theory  of  Haeckel,  792 
Gastric  digestion,  79 
Gastric  juice,  70 

action  of,  78,  80 

action  on  bacteria,  82 


Gastric  juice,  chemical  analysis,  71 

composition  of,  71 

excitants  of  flow,  70.  76 

effects  of  bitters,  78 

fat-splitting  ferment,  SO 

fistula  for,   70 

flow  of,  74 

function,   79,  80 

methods  of  securing,  77 

mixed,  80 

pepsin  of,  79 

reaction  of,   71 

secretion  of,  71 

specific  gravity,   71 

theory  of  non-digestion  of  stomach,  82 

varies  in,  composition  and  rate  of  se- 
cretion, 74,  75 
Gastrula,  779 

Gay-Lussac-Van't  Hoff  law,  134 
Gelatin,  37,  424 
Geniculate  bodies,  578 
Genito-spiual  center,  608 
urinary  apparatus,  417 
Germinal  cells,  769 

epithelium,   771 
Germplasm,  769 
Genu,  582 
Giantism,  372 
Glands  (see  names  of). 
Glands  of  intestines,  89 
Glass-blower's  pulse,  350 
Glisson's  capsule,  106 
Globulins,   35,  36 
Glomerules  of  kidney,  389 
Glossokinesthetic  center,  501 
Glossopharyngeal  nerve,  65,  763 

distribution,  764 

function,  764 

origin,  764 

pathology,  764 

physiology,   764 
Glottis,  496 
Glucose,   28 

secretion,  119,  C12 
Glycocholic  acid,  111 
Glycogen,  116,   117,  118 
Glycosamin,  104 
Glycosuria,  118 
Gmelin's  test  for  bile.  112 
Golgi  stain,  529 
GoU's  column,  559 
Gower's  column,  547 
Graafian  follicle,   787 
Gram  calorie,  441 
Gram  molecule  solution,  137 
Grandry  corpuscles,  657 
Gray  matter  (see  cerebellum,  etc.). 
Great  longitudinal  fissure,  570 
Great  transverse  fissure,  570 
Growth  and  development,  432 
Guaiac  test  for  blood,   199 
Gullet  (see  oesophagus). 
Gunsberg's  test  for  hydrochloric  acid,  S3 
Gustometer,   Sternberg's,   302 
Gyrus  fornicatus.  575 

hippoeampus,  576 

Habenula,  578 
Htemacytometers,  167 

Thoma-Zeiss,  168 
Hwmaglobinuria,  405 
Hiemianopsia,  747 
Hffimatachometer,  276 
Htematoblasts,  177 
H;pmatocrit,  169 

Daland's,  168 
Htematoidin,  183 
Haematoporphyrin,  182 
Hffimatin,  181 


804 


INDEX. 


Hpcmin,  181 

chemical  properties  of,  182 

crystals,  181 

tests  for,  181 
Hajmochromogen,  186 

ispectrum,  186 
Hemoglobin,  179,  181 

amount,  187 

characteristics,  181 

composition,  181 

crystallization,   181 

estimation  of  percentage,   187 

reduced,   186 

variations   in   amount,    187 
HEemolysins,  295 

physiological  analogy,  290 
Hffimometcr,  187 

Dare's,  188 

Von  Fleischl's,   188 
Hsemorrhage,  196 

effects  of,  196 

quantity  of  blood  in,  196 
Hair,  662 

chemical  composition,  663 

function,  G63 

general  description,  663 
Hale's  blood-pressure  experiments,  265 
Hay's  test  for  bile.  111 
Hearing,  677 

anatomy  of  organ  of,  677 

auditory  nerve,  685 

binaural  audition,  695 

Eustachian  tube,  690 

general   description,   677,   678 

organ  of  Corti,   684 

semi-circular  canals,   696 

sense  of,  653 

theory  of,  694 
Heart,  208 

accelerator  center,  235 

action  of  vagus  on,  234 

areas  of  audibility,  224 

arteries,  240 

auricles,  210 

causes  of  sounds,  221 

changes  in  shape  and  position,  213 

chordae  tendinese,  206 

course  of  blood  in,  311 

diphasic  variation  of,  521 

effects  of  drugs  on,  242 

endocardium,   208 

foramen  ovale,  204 

foramina  Thebesii,  205 

frequency,  227 

ganglia  of,  232 

His's  muscular  bundle,  232 

histology  of,  208 

innervation  of,  234 

lymphatics  of,  208 

minimal  stimuli,  243 

moderator  center,  235 

movements  of,  214 
to  clinicians,  214 
persistence  of,  220 

muscles  of,  208 

musculi  pectinati,  204 

myocardium,   208 

nerves  of,  234 

nutrition  of,  245 

papillary  muscle,  206 

position  of  valves,  207 

refractory  period  of,  244 

revolution  of,  213 

rhythm  of,  230 

sinus  of  Valsalva,  207 

size  and  shape  of,  203 

sounds  of,  222,  223,  224 

stair-case  contraction,  244 

Stannius's  experiments,  231 

stimuli,  243 


Heart,  structure  of,  208 
sympathetic  fibers  to,  241 
valves  of,  207 
mitral,  207 
position,   224 
semilunar,  207 
tricuspid,   206 
ventricles  of,  208 
work  of,  228 
Heat   (see  temperature), 
animal,  434 
estimation  of,   441 
latent,  435 
other  sources,  436 
radiant,  435 
theory  of,  435 
Heat-spots,   661 
Heat  value  of  food,  431 
Heat  unit,  441 
calorie,  441 
calorimeter,   442 
Height,  relation  to  lung  capacity,  318 
Helicotrema,   683 
Heller's  nitric  acid  test,  411 
Hemianopsia,  471 
Heidenhain's  lymphagogues,   156 

theory  of  secretion,  156 
Hensen's  cells,  685 
Hensen's  disk,  460 
Heredity,  791 

Hering's  theory  of  color,  735 
Hiatus,  683 
Hibernation,  438 
Hiccough,  339 
Hippuric  acid,  401 
formation  of,  401 
where  secreted,  401 
His's  muscular  bundle  of  heart,  232 
Histology,   3 
Histones,  37 
Hoarseness,  500 
Hormone,  76,  97 
Horopter,  731 
Hunger,  128 
Hyaloplasm,  9,  524 
Hydrsemia,  198 

Hydrochloric  acid,  71  , 

ion  theory  of,  73 
stimuli  for  secretion,  73 
test  for   (Gtinsberg),   83 
Hydroxamino   acids,   104 
Hypermetropia,  724 
Hyperosmia,   6'75 
Hyperphoria,  739 

Hyperpyrexia,  cause  of  death,  455 
Hypoblast,  782 
Hypoglossal  nerve,  768 
anastomoses,  768 
origin,  768 
pathology,  768 
physiology,  768 
Hypoxanthiu  in  urine,  402 

IGNOTIN,   39 

Ileocsecal  valve,  89 

Ilium,  85 

Image,  formation  on  retina,  731 

Immunity,  291 

Inanition  or  starvation,  425 

Incus,  681 

Indican,  405 

test  for,   405 
Indigestible   residue   of   fgeces,    126 
Indirect  cell-division,  20 
Indol,   124,   126,   405 
Inferior  vermiform  process,   613 
Infundibulum,  306 
Inoculation   (see  immunity). 
Inorganic  salts  of  faeces,  126 
Inoslte,  471 


INDEX. 


805 


Insalivation,  E>7,  62 
luhcritanc'c,  791 
Inspiration,  310 

expansion  of  chest  in,  313 

extraordinary,  314 

movements  of,  313 

movements  of  blood  in,  325 

muscles  of,  313 
Inspiratory  center,  333,  610 
Intensity  of  sound,  491 
Intermedio-lateral  column,  543 
Intermittent  afflux  apparatus,  253 
Internal  capsule,  oS2 
Interpedunculear  space,  565 
Interstitial  slits,  148 
Intestinal  digestion,  122 
Intestine,  85,  89 

blood-supply,  88,  89 

coats,  86,  90 

digestion  in,  122 

gases,  124 

glands,  89 

large,  89,  90 

length,  85 

movements  of,  90 

nerve-supply  of,  91 

small,  85 

structure,  86 
Intracellular  ferments,  28 
Intraocular  pressure,  718 
Intrapleural  pressure,  323 
Intrathoracic  pressure,  322 
Inunction,   158 
Inverted  images,   731 
Invertin,  28 
lodothyrin,  362 
Ions,   130 

necessary  for  solution,  131 

system  of  naming,  131 
Iris,   707 

ciliary  processes,  705 

nerves,  708 

pigment,  708 

reflex,  612 

reflex  movement  of,  612 

uses,  708 
Iron,   27 
Irradiation,  736 
Irritability.  467 
Ischuria,  680 

Islets  of  Langerhans,  95,  102 
Isotonic  solution,  135,  170,  245 

Jacobson's  nerve,  764 
Jaundice,  121 
Jecorin,  113 
Jejunum,  85 
Juices   (see  names  of). 

Karyokinesis,  20 

stages  of,  22 

time  of,  22 
Keratin,  37 
Kephir,  41 

Kjeldahl  process,  395 
Kidney,  383 

blood-vessels  of,  391 

calyces  of,  387 

capillaries  of,  392 

capsule  of,  385 

cavity  of,  301 

cortex  of,  388 

extirpation  of,  414 

general  description  of,  385 

glomerules,  389,  391 

hilus,  384 

lymphatics,  382 

Malpighian  corpuscles  of,  391 
pyramids  of  Ferrein,   391 

medulla  of,  388 


Kidney,  minute  anatomy  of,  388 

parenchyma  of,   388 

position  of,  383 

sinus  of,  385 

structure  of,  385 

urinary  tubules  of,  389 
Knee-jerk  or  patellar  reflex,  608 
Krause's  end-bulbs,   657 

membrane,  462 
KumysSj  41 
Kymograph,  267 
Kyrines,  36 

Labyrinth  of  ear,  681 
Lacrymal  gland,  740 
Lacrymal  secretion,  742 
Lactalbumin,  41 
Lacteals,   88,   142,   143 
Lactose,  41 
Lactic  acid,  41,  401 

Uffelman's  test,  83 
Lactic  acid   bacillus,  41 
Lactic  fermentation,  41 
Lactose,  28 
Lamper  eel,  2 
Lamina  denticulatum,   538 

spiralis,  682 
Langerhans's  cells,  95,  102 
Lantanin,  12 

Lanterman's  incisures,  531 
Large  intestine,  46,  89,  90 
Laryngoscope,  496 
Larynx,  492 

'anatomy  of,  492 

cartilages  of,  493 

cavity  of,  496 

condition  of,  496 

muscles  of,   494 

nerves  of,  496 

pathology  of,  500 

vocal  cords  of,  496 
Lateral  chain  theory  of  Ehrlich,  292 
Lateral  columns,  546 
Lateritious  deposits,  400 
Laughing,  339 
Law  of  Fechner,  653 
Laws  of  sensation,  653 
Lecithin,  113 
Lemniscus,   568 
Lens,  crystalline,  709 
Lenses,  726 

Lenticular  nucleus,  579 
Leucine,  99,  103 
Leucocytes,  170 

eosinophiles,  171 

mononuclear,  172 

polymorphonuclear,  172 

transitional,  172 
Leukocytosis,  171 
Levulose,   28 
Lieberkiihn's  glands,  89 
Life  period,  1 

Ligamentum  denticulatum,  538 
Light,  699 

perception  of,  517 

theory  of,  699 

transmission  of,  699 
Lime  salts  in  metabolism,  428 
Linin,  12 
Lipase,  61 

reversible  action  of,  61,  101 
Liquor  sanguinis,  163 
Lissauer's  tract,  549 
Liver,  105 

antitoxic  function  of,  116 
blood-supply  of,  106 
daily  secretion,  109 
diastase  of,  118 
extirpation  of,  116 
function  of,  108 


806 


INDEX. 


Livor,  gall-bladdpr,  108 

internal  secretion  of,  116 

reaction  of,   100 

specific  gravity  of,   109 

structure  of,   107 
Locus  cocruleus,  567 
Locus  niger,  565,  622 
Ludwig's  tlieory  of  lympli,  156 

strolimur,   275 
Lungs,  304 

air-pressure  in,  323 

air  sacs,  306 

blood-supply,  307 

color,  305 

coverings,   308 

diffusion  of  gases  within.   343 

lobes,  304 

lymphatics,  308 

medico-legal  test,  305 

nerves,  308 

roots,  304 

structure,  306 

vital  capacity,  319 
Luxus  consumption,   42G 
Lymph,   151 

coagulation,  151 

composition,  152 

flow  of,  153 

formation  of,  155 

quantity  of,  157 

relation   to  nervous  system,   154 

theories  of  secretion,   155 
Lymphagogues,  156 
Lymphatic  glands,  150 
Lymphatic   system,    148 
Lymphatic  trunk,  etc.,  146 
Lymphatic  vessels,   145,  150 
capillaries,  147 
coats   of,   147 
development  of,  148 
distribution  of,  146 
origin  of,  148 
structure  of,   146 
valves  of,  147 
Lymphocytes,   152,   171 

large   non-nuclear,   172 

small   non-nuclear,    171 

Maculae,  713 

Macula  lutea,  713 

IVIagnesium   salts   in    metabolism,    428 

Malpighian   corpuscles,   3 

of  kidney,   391 

of  spleen,    364 
Malleus,    681 
Maltase,  61 
Maltose,  28,  29 

Maly's   theory   of   gastric   secretion,   73 
Male  pronucleus,  777 
Mammary  glands,  372 

arteries  of,    374 

during  pregnancy,  788 

general  description,  373 

lymphatics,   374 

nerves,   374 

results  of  dried,  .376,   788 

structure  of,  375 
Manometer,   265 
Marey's  intermittent  afflux  apparatus,   254 

tympanum,  316 
Mastication,   56,   57 
Mast  cells,  172 
Mastoid  cells,   680 
Matter,  1 
living,  1 
Maturation  of  ovum,   775 
Matzoon,  41 
Meat,  38 
Meconium,  126 
Medico-legal  tests  for  blood,   199 


Medulla  oblongata,  551 
ala  cinerea,  556 
anterior  pyramids,  553 
arcuate  fibers,  560 
auditory  strias,  555 
bulbar  nerves,   610 
calamus  scriptorius,  550 
centers  of,  610 
olava,  555 

double  conduction,  609 
external  form,  552 
fillets,   568 

formatio  reticularis,  557 
fourth  ventricle,  566 
funiculus  cuneatus,  556 

gracilis,   556 
general   description,  552 
internal  structure,   557 
lateral  columns,  559 
nucleus  lateralis,  557 
olives,   560 
parts  added,  560 
posterior  columns,  559 
raphe  of  Stilling,  557 
restiform  body,  553,  555 
trigonum  hypoglossi,  556 
weight,  552 
white  columns,  558 
white  substance,  558 
Meissner's  plexus,  91 
Melanin,   655,   733 
Membrana  basilaris,  683,   694 
granulosa,   775 
tympani,    688 
Membranes   of  cord   and   brain,   537 
Membranes,    mucous    (see    names   of). 
Membranous  labyrinth,  683 
Memory  center,  631 
Menopause,  786 
Mesoblast,   782 
Mesoderm,  782 
Mesoporphyrin,  183 
Metabolism,  423 
anabolic  processes,  420 
balance  of,  422 
catabolic,  420 

effect  of  starvation  on,  425 
effect  of  work  on,  474 
equilibrium,   424 
general  explanation,  420 
of  carbohydrates,  427 
fats,   426 
salts,    428 
tabulated  exchange,  430 
Meta-proteins,  34 
Metazoa,  772 
Methsemoglobin,  183 

spectrum  of,  187 
Mett  proteid   method,  73 
Metric   system,   794,   795 
Micro-organisms  of  fteces,  126 
Microscopic  test  for  blood,  199 
Microspectroscope,   183 

Sorby    Browning's,    182 
Micturition,   418 

Midcerebellar  peduncles,  562,  621 
Middle  ear,  679 
Milk,  40 
clotting  of,   41 
colostrum  of,  42,  376 
cow's,   40 
fats  of,   42 
fermentation  of,  41 
functional  variations  of,  42,  376 
matzoon,  41 
microscopically,  40 
proteids  of,   41 
quantitative,   40 
quantity  secreted,   42 
reaction,  40 


INDEX. 


807 


Milk,  salts  of,   42 

secretion  of,   42 

specific  gravity,  40 

theory  of  Ottolcnghi,  370 

woman's,   42 
Milk-curdling  ferments,  41 

globults,  40 

sugar,  41 

teeth,  49 
Mitosis,  20 

stages  of,  22 
Modiolus,  682 
Mol,   137 
Molars,  GO 

Molecular  theory  of  nerve  currents,  r>22 
Molecules,  5 
Monamino  acids,  32,  103 
Mononuclear   leucocytes,    172 
Monosaccharides,  28 
Morphology,  2 
Morula,  777 
Motion,  1 

Motor  area,   extirpation   of,   G28 
Motor  areas,  G25 

impulses  transmitted,  590 

speech-center,  501, 

tract,   584 

writing  center,  501 
Motor  oculi  nerve,   751 
distribution,   751 
diplopia,  753 
drugs,  action  upon,  753 
function  of,   751 
origin  of,  751 
pathology  of,  753 
Motor  spray,  4G5 
Motor  tract,  584 
Mouth,   4(i,  47 
Movement  in  a  circle,  (121 

of  protoplasm,  15 
Mucin,   35 

Mucous  membranes   (see  names  of). 
Miiller's  law,  G50 
Muroxid   test,   401 
Muscarine,  242 

action   on   heart,   242 
on  respiration,  328 
Muscle-curve,   475 

effect  of  stimuli  upon,  477 
summations  of  stimuli,   480,   481 
tetanus,  482 
Muscles,  456 

appearances  under  polarized  light,  4G3 

as   perfect  machines,   4SG 

blood-vessels  of,  464 

carbohydrates  of,   470 

cardiac,  4G6 

changes  in  contraction,  478 

chemical  excitants,  46 

chemistry  of,  470 

Cohnheim's  areas,  461 

contraction  period,  475 

constituents  of,   470 

contractility  of,   467 

curve,   475 

elasticity  of,  484 

electrical  phenomena  of.  518 

extractives,  471 

fatigue,   477 

ferments,    471 

fibers.  462 

general  description,   457 

Hensen's   disc,   4G0 
•influence  of  blood  upon,  467 

involuntary,   466 

latent   period,    475 

longitudinal    striations,    460 

nerve-supply,   464 

nerve-stimuli   of,   469 
chemical.    469 


Muscles,  nerve-stimuli,  electrical,  469 
mechanical,  469 
thermal,  469 

nuclei   of,   466 

proteids  of,  470 

rate  of  contraction  of,  478 

reaction  of,  470 

relation  to  tendons,  464 

relaxation  period,  476 

resting  and  acting,  478 

rigor  mortis,   472 

sarcous  elements  of,  460 

serum,  471 

sounds  of,  483 

striated,   456 

structure,   458 

tension  of,  484 

tetanus  of,   482 

theories  of  currents,  519 

tonus,   483 

unstriped,  466 

urea  in,  470 

varieties  of,  456 

voluntary,   456 

voluntary   contractions  of,   483 

wave,  478 

wing  muscles  of  insects,  461 

work  of,   485 
Muscular  labor  and  urea  excretion,  474 
Muscular  sense,  651 

center  of,  630 
Mutation  theory,  793 
Myelin,   530 

Myograph,   pendulum,  473 
Myogram,  475 
Myopia,  724 
Myohfematin,  470 
Myosin,  470 
Myosinogen,   470 
Myxcedema,  361 

Nails,  663 
general  description,  GG3 
function,  664 
Narcotics,  637 
Near  point  of  eye,  724 
Neosin,   39 

Neovitalists,  school  of,  155 
Nerve,   comparison  with  muscle,  587 
effects  of  anajmia  upon,  602 

electricity  upon,  594 

temperature  upon,  588 
electrotonus,  594 
electrical  potential   of,   521 

current,  theories  of,  522 
excitability  of,  .587 
excitability   and   conductivity,   591 
excitants,  591 

chemical,  591 

electrical,  594 

mechanical,  591 
influence  of  blood  upon,  602 
irritability  of,  588 
Kiihne's  experiment,  590 
Pflueger's  contraction  laws,   594 
regeneration,   532 
roots  of,   550 

stable  equilibrium  of,  588 
table  of  degenerations,  550 

ascending,  550 

descending,  550 
Nerve-cell,  524 

classification  of,  533 

dendrons  of,  528 

dimensions  of,  529 

fibrils,  528 

neurite,   528 

Nissl's  granules,   527 

nucleolus  of,  527 

nucleus  of,  527 


808 


INDEX. 


Nervc-ccll,  prolongations  of,   r)28 
staining,   529 
structure,   524 
Ncrvc-ccuters,  535 

common  points  of,   536 
Ncrve-fibors,  531 
centrifugal,  605 
centripetal,  605 
chenii('al  properties  of,   534 
fatigue  of,   4S,S,   5S9 
meclianical   properties  of,   535 
niedullated,   531 
myelin,  530 
neurilemma,  531 
nodes  of   Ranvicr,   531 
non-medullated,   531 
reaction  of,  535 
terminations  of,  532 
Nerve  metabolism,  535 
Nerve-muscle  preparation,   515 
Nerve-tissue,  534 
composition,  534 
gray,  533 
reaction  of,  535 
structure  of,  535 
trunks,  531 
white,  534 
Nerve-wave,    transmission   of,    589 

swiftness  of,    591 
Nerves  of   deglutition,   59 
heart,  234,  236,  23S 
intestines,  91 
larynx,  496 
Jacobson,   764 
respiration,   331 
salivary  glands,  55 
sweat  glands,  381 
taste,  666 
tongue,  666 

vasomotor  system,  279 
Nervous   system,   524 
anatomy  of,   524 
chemistry  of,  534 
extra-cardiac,  234 
lecithin,  534,  535 
metabolism  of,  535 
neuroglia,  542 
Neurilemma,  531 
Neurites,   528 
Neuroglia,  542 
Neurokeratin,   534 
Neutral   fats,  29 
Neutrophiles,  171 
Ninsen's  globules,  376 
Nissl  bodies,  527 
Nitrogen  eliminated,   430 
equilibrium,  424 
estimation,  430 
in  blood,  349 
in  respiration,  349 
Nodal  points  of  eye,  720 
Nodes  of  Ranvier.  531 
Nonsexual   reproduction,  770 
Nose  (see  smell). 
Novain,  39 

Nuclear  membrane,   13 
sap,  12 
spindle,  21 
substance,   12 
Nuclei  of  cerebellum,  614 
Nuclein,  13 
Nuclei  pontis,  563 
Nucleolus,   12 
Nucleoproteids,   35 
Nucleus,  7,  11,  13 
composition,  13 
form,  12 
number,  12 

relative  importance  of,  11 
size,  12 


Nucleus,  structure,  12 
Nucleus,   Deiters's,   687,   698 

emboliformis,  614 

fastigii,  614 

globosus,  614 

lateralis,  557 
Nutrition,   1 

Nuttall's  guinea-pig   foetus,    124 
Nystagmus,  753 

Obesity,  432 

Banting's  method,   432 

Oertel's  method,   432 
Oblitin,   39 
Oculomotor,  751 

diplopia,   753 

effect  of  drugs  on,   753 

function   of,   751,   752 

pathology   of,    753 
Odors,   674 
ODsophagus,  46,  56 

length,   56 

anatomy,   56 

nerves,    56 
ODstrus,  787 
Olein,    30 
Olfactory  bulb,  673 

cells,   673 

mucous  membrane,  671 

nerve,   672 

organ,  672 

sensations,  673 
Olives,  553,  564 
Oncometer,  290,  365 
Open   pores,   149 
Ophthalmoscope,  742 
Opsonins,  297 
Optic  angle  (eye),  731 

axis,   730 

commissure  of  Gudden,  719 

nerve,  714 

thalamus,  578,  623 
Organic  compounds  in  body,  25 
Organ  of  Corti,  684 

taste,  665 

voice,  492 
Organs,  4 
Origin  of  species,  791 

of  life,   793 
Orthophoria,  693 
Osmosis,  132 
Osmotic  pressure,  133 
determination  of,   134 
of  lymph,   135 
proteids,   135,   137 
physiological   application,   137 
Osseous  labyrinth,  682 
Ossicles,  681,  691 
Otic  ganglia,   641 
Otitis  media,  679 
Ovary,  775 

internal  secretion,  787 
Ovists,  771 
Ovum,  775 
Oxalic  acid,  401 

fermentation,  124 
Oxidation,  349 

seat  of,  344 
Oxybutyric  acid,   120 
Oxygen  in  bloofl,  341 
Oxyhemoglobin,    181 

spectrum,   186 
Oxyntic  glands,  68 

Pacinian  corpuscles,  657 
Pain,  659 
Palate,  48 
Palmatin,  43 


INDEX. 


809 


Pancreas,  94 

blood-supply  of,  95 

composition  of,  98 

daily  amount,  98 

effects  of  removal,  101 
injection  of  extract,  104 

methods  of  obtaining  the  juice,  98 

nerve-supply  of,   95 

reaction  of,  98 

removal  of,  101 

secretion  of,  95,  96,  97 
adaptation  of,  97 
excitants  of,  97 

secretory  nerves  of,  97 

specific  gravity,  98 

structure  of,  94 
Pancreatic  juice,  98 
composition  of,   98 
ferments,  99 
quantity,  98 
reaction,  98 
specific  gravity  of,  9S 
Papillte  of  tongue,  49,  GGG 
Papain,  100 

Paracerebellar  nuclei,  C20 
Paraglobulin,   36 
Paranuclein,  13 
Parasympathetic,  040 
Parietal   cells,   68 
Parieto-occipital   fissure,   571 
Parathyroid  gland,  362 
Parotid  gland,  54 
Parthenogenesis,   770 
Pathetic  nerve,  753 
distribution,  753 
function,  754 
origin,  754 
pathology,  754 
Pav.'low's  stomach,  77 
Peduncles  of  cerebellum,  621 
Pelvis   of  kidney,   386 
Pendular  movements,   91 
Pendulum  myograph,  473 
Pepsin,  71,  72 
Pepsinogen,  73 
Peptic  digestion,  80 
Peptone,  36,  99 
Peptonuria,  410 
Perception  time,  638 
Pericardium,  209 
Perilymph,  693 
Perimeter,  743 
Peristalsis,  90 

infiuence  of  drugs  on,  93 

of  intestines,  90 

pendular  njovement,   91 
Perivascular  space  of  His,  148 
Permanent  teeth    (see  teeth). 
Perspiration,   380 

acidity  of.  380 

constituents,  380 

effect  of  drugs  upon,  381 

function   of,   382 

insensible,  378 

nerve-centers,   382 

nerves  of,  381 

pathological,  382 

relation  to  lung  excretion,  382 

role  of,  382 

sensible,  378 

suppression  by  cold,  382 
Petit,   canal  of,   716 
Petrosal  nerves,  762 
great,  762 
small,    762 
Pettenkofer's  test  for  bile.   111 
Peyer's  patches,  89 
Pfeiffer's  phenomenon,  295 
PfJiigcr's  contraction  laws,   594 
Phagocytes,  16,  173 


Pharynx,  55 
openings,  55 
anatomy,  55,  56 
Phenol,  124 

Phenylhydrazin  test  for  sugar,  413 
Phenomena  of  life,   1 
Phrenic  nerve,  329,  331 
Phloridzin,   119 
diabetes,  119 
Phosphenes,   737 
Phosphoric  acid,  406 

sediments,   410 
Phylogenesis,   792 
Phylloporphyrin,  183 
Physical   heat,   434 
Physiology,  2 
Pilomotor   nerves,  645 
Pia  mater,  537 
Pitch,  498 

Picrocarmin  spectrum,  187 
Pituitary  body,  371 

extirpation  of,  372 

extracts  of,  372 

lobes  of,  372 

position,   371 

size,  371 

structure,  372 
Placenta,   789 
Plantar  reflex,  600 
Plasma  of  blood,  189 

chemical   properties  of,  189.   190 

gases  of,  191,  347 

inorganic   constituents  of,   189 

method  of  examining,  189 

organic   constituents  of,   190 

physical   properties  of,   188 
Plasmodium  malarias,  166 
Plasmon,   41 
Plethysmograph,  290 
Plethora,  198 
Pleura,  308 

Plexus   (see  names  of). 
Pneumogastric  nerve  (see  vagus),  234,  765 

branches  of,  765 

function  of,  766 

influence  on  deglutition,  59 
gastric  secretion,  77 
heart,  235 
lungs,  331 
pancreatic  juice,  97 
vomiting,   84 

pathology  of,  766 

physiology   of,   766 
Pneumograph,  315 
Poiseuille's  still  space,  262 
Polar  bodies,  775 

Polymorphonuclear  leucocytes,   172 
Polypeptids,  32 

groups,  33 
Polysaccharides,  28 
Pons  Varolii,  560 

center  of  epileptiform  convolutions,  621 

central  nucleus,   564 

faces,  560 

general  description,  560 

stratum  complexium,  562 
profundum,  562 
zonale,  563 

structure,   562 

trapezoid  body,  562 
Portal  circulation,  106 
Portal  vein,  106 
Posterior  columns,  548 
Posterior  fovea,  567 
Posterior  perforated  spaces,  565 
Posterior  root-fibers.  550 
Postganglionic  fibers,   639 
Precipitin  lest  for  blood,  199 
Precipitins,  294 
Preganglionic  fibers,  639 


810 


INDEX. 


Pregnancy,   788 
Prehension,  47 

of  cow,  47 
frog,  47 
horse,   47 
man,  47 
squirrel,   47 
Presbyopia,  724 
Prostate   gland,   785 
Proopstrus,  787 

Pressure  curve  of  ventricle,  21!) 
Protamines,  37 
Proteases,  61 
Proteid  compounds,  35 
Proteids,  31,   32,   425 

absorption  of,  140 

chemical   composition  of,   31 

chromoproteids,  35 

classification  of,  34 

heat  value  of,   431 

metabolism  of,  425 

nucleoproteids,   35 

of  muscle,   486 

where  found,  34 
Proteins,   34 
Proteoses,  36,  128 
Prothrombin,   193 
Protoplasm,  8 

chemical  composition,  9,  10 

constituents  of,    10 

definition   of,    8 

importance  of,  19 

movements  of,  14 

movements,   rate  of,   15 

specific  gravity,   10 
Protoplasmic  movement  of  leucocytes,   15 
Proximate  principles,  26 
Ptyalin,  60 
Pulmonary  artery,  pressure,   353 

action  of  drugs  upon,  353 
Pulse,  255 

dicrotic,  258 

factors  necessary  for,   25S 

qualities  of,  256 

glass-blower's,  350 
Pulse,  respiration  ratio,  227 
Pupil,   70S 

cause  of  dilatation  of,  709 
Purin,  399 
Purkinje  cells,  617 
Purkinje-Sanson  images,  726 
Putamen,  580 

Putrid  products  of  faeces,   126 
Pyloric  glands,  68 
Pylorus,  66 

closure  of,  70 
Pyramidal  tracts,  545,   546 
Pyramids  of  kidney,  388 
Pyrimidine  bases,   32 
Pyrenin,  13 
Pyrrolidine,  32,  104 

Quickening,  788 

Quotient  of  gases,   respiratory,   345 

Ranvier,  nodes  of,  531 
Rarefied  air,  352 
Reaction   time,   638 

of  light,  638 

of  motor  impulses,  638 

of  sound,  638 

of  touch,  638 
Rectum,   127 
Reduction  division,  777 
Referred  sensations,  648 
Reflex  action,  seat  of,  599 

forms  of,  606 

law  of   co-ordination,   601 
irradiation,   601 


Kedex  action,  laws  of,  601 
localization,  UUl 
other  seats,   599 
skin,  609 
swiftness  of,  GDI 
tendon,  607 
Reil,  island  of,  573 
Reissner,   membrane  of,  683 
Remak's  ganglion,  232 
Renal  circulation,  392 

oncometer,  414 
Rcnnin,   41,   73,   100 
Reproduction,  769 

among  higher  animals,   770 

among  lower  animals,  770 

chorion,   783 

epiblast,   782 

fecundation,  777 

fertilization,   777 

foetal   circulation,   790 

hypoblast,  782 

menstruation,   785 

mesoblast,   782 

non-sexual,  770 

ovum,  775 

ovum,  maturation  of,  775 

parthenogenesis,  770 

placenta,  789 

segmentation,  777 

sexual   reproduction,   770 

spermatozoon,  783 
structure  of,  783 
Reserved   air,   319 
Residual   air,   319 
Resonance,   498 
Respiration,  308 

abdominal   type,   315 

action  of  drugs  upon,  340 

air-passages,  306 

alveoli,  307 

apparatus,  301 

artificial,  327,  336 

bronchi,  306 

carbon  monoxide,  351 

center  of,  328 

chemistry  of,  340 

Cheyne-Stokes  respiration,   340 

compressed  air  in,  352 

curious  phenomena  of,  348 

effect  on  blood-pressure,  324 

effect  on  circulation,  322 

effect  on  pulse,  326 

expiration,  314 

external,  301 

function  of,   300,  301 

function  of  unstriped  muscular  of  bron- 
chi,  327 

gases  in,  350 

inferior  costal  type,  315 

internal,  301 

inspiration,  310 

lungs,  304 

lymphatics,   308 

mechanism  of,  308 

modified  movements  of,  338 

nasal,  327 

nerves  of,  329,  331 

number  of,  320 

of  different  forms  of  life,  300 

of  chick,  300 

of  fnetus,    300 

pathological,  320,  328 

pressure  in,  321 

quotient  of  gases,  345 

relation  to   nervous  system,   328 

rarefied  air,   353 

sounds  of,  317 

superior  costal  type,  315 

trachea,   302 
Respiratory  undulfitions,   272,  323 


INDEX. 


811 


Restiform  body,  555 
Rete  Malpighii,  655 
Reticulated  nucleus,  563 
Retina,  710 

blind  spot,  728 

duration  of  stimulation,  737 

epithelium,  713 

histological,  711 

hyaloid  membrane,  71G 

lymphatics,  718 

pigmentary  membrane,  713,  715 

rods  and  cones,  710 

terminal  nerve  elements,  712 
Retina!   epithelium.   713 
Rheonome  of  Von   Fleischl,  513 
Rheotome,   differential,   514 
Rheoscope,  physiological,  516 
Rhodopsin  or  visual  purple,  713,  732 
Ribs,   action   in   respiration,   313 
Rigor  mortis,  472 
and  tetanus,  482 
cause  of,  472 
influence  of  fatigue,  474 
influence  of  temperature,  472 
Rolando,  fissure  of,  571 
Rosette,  21 

Saccharoses,  28 
Saccule,  698 
Saliva,  60 

action  on  starch,  60 

composition  of,  62,  63 

ferment  of,  60 

mechanical  function  of,  57 

reaction  of,  62 

reflex  centers,  65 

specific  gravity  of,  62 

temperature  variations  in,  02 

time  of  activity,  62 
Salivary  glands,  54,  55,  63 
action  of,  62 

of  drugs  on,  63 
nerves  to,   63,  64 
Pawlow's  experiments,   65 
reflex  centers  of,  65 
structure  of,  55 

trophic  and  secretory  fibers,  64 
Salts,   27,   88 

in  body,  27 

in  metabolism,  428 

in  urine,  406 
Santorini'a  cartilage,  493 
Saponification,  30 
Sarcolactic  acid,  470 
Sarcolemma,  458 
Sarcomeres,  460 
Sarcoplasm,  460 
Sareostyles,  460 
Scala  tympani,  683 
Scala  vestibuli,  683 
Scapular  reflex,  607 
Schafer's  artificial  respiration,  337 
Schuetz's  law,  73 
Scheiner's  experiments,   730 
Schmidt,  segments  of,  531 
Schwann,   white  substance  of,   530 
Science,  2 

biological,  2 

physical,  2 
Scleroproteins,  36 
Sclerotic  coat,  700 
Sebaceous  glands,  661 

function  of,  662 
Secretin,  97 
Secretion,  355 

adrenal,  365 

by  filtration,  355 

by  filtration  proper,  3.56 

by  glandular  desquamation,   356 

external.  372 


Secretion,  external,  mammary,  372 
sweat,  377 
urinary,  383 
internal,  357 
morphological,  356 
pancreas,  95 
pituitary  body,  371 
spleen,  364 
thymus,  370 
thyroid,   357 
Sediments  in  urine,  410 
in  acid  urine,  410 

alkaline  urine,  411 
amorphous,  399 
Segmentation,   777 
Segmentation  nucleus,  777 
Semen,  "83 

spermatozoon,  773 
Semicircular  canals,  6S2,  696 
Cyon's  theory,  697 
Ewald's  theory,  696 
reflex  center  of,  698 
Semilunar  valves  (see  heart-valves). 
Sensibility,  1 
Seminiferous  tubules,  773 
Sensation  of  color,  734 
Sense  spots,  653 
Sensory  centers,  625 
Sensory  relay  centers,  623 
Sensory   tract,   586 
Serum  albumin,  34 

of  bacteriolytic  cholera,  295 
of  blood,  189 
globulin,  189 
normal,   188 
Sham  feeding,  76 
Shock,  196 

Side-chain  theory,  292 
Sighing,  33S 
Sight,  699 

Sigmoid  flexure,  90 
Sinus  of  Valsalva,  207 
Sixth  cranial  nerve,  755 
Skatol,  124 
Skin,  653 
action  of  liquids  on,  660 
action  of  solids  on,  659 
cold  spots,   661 
corium,  655 
epidermis,    653 
hot  spots,  661 
Krause's  end  bulbs,  657 
layers  of,  654 

radiation  and  conduction,  4.52 
reflexes,   606 
rete  Malpighii,  655 
stratum  corneum,  655 
granulosum,  653 
lucidum,  653 
touch  corpuscles  of,  656 
Sleep,  6.34 

theories  of,  635 
Small  intestine,  85 

innervation  of,  89,  91 
Smell,  sense  of,  670 
anosmia,  675 
center  of,  626 
general  description  of,  671 
hyperosmia,  675 
mechanism  of,  674 
nerves  of,  672 
olfactory  organ,  672 
olfactory  sensation,  673 
proper  stimulus  of,  673 
secondary   sensations,   674 
subjective  sensations,  674 
uses  of,  675 
Snoring,  339 
Soap,  30 
Sobbing,  339 


S12 


INDEX. 


Sodium  chloride,  27 
in  blood,    189 
in  urine,  40G 
substitutes  for,  27 
Solitary  glands,  89 
Solutions,  gram  molecule,  137 
Somatose,  82 
Sound,  497 
height  of,  497 
intensity  of,  49 

production  and  modification  of,  491 
resonance  of,   498 
timbre,  498 
Sound-waves,   course  of,  C93 

conduction  of,   G90 
Sounds  of  heart,  221 
variation  in,  225 
Special   cell-constituents,    7 
sensation,   laws  of,  G53 
senses,  650 
Spectra  of  blood,  184 
Spectroscope,  183 
Spectroscopic  test  for  blood,  199 
Speech,  499 
aphonia,  500 
center  of,  501 
defects  of,  500 
hoarseness,   500 
stammering,  500 
stuttering,  500 
ventriloquy,   499 
Spermatogenic  cells,  773 
Spermatozoon,  774 
structure  of,  774 
Sphenopalatine  ganglion,  759 
Spherical  aberration,  722 
Sphincter  ani,  127 
Sphygmogram,  259 
Sphygmograph,  257 

Marey's,  257 
Sphygmometers,  269 
Erlanger's,   271 
Mosso's,  270 
Riva-Rocci's,  270 
Sphygmomanometers,  269 
Spinal  accessory,  767 
distribution,   767 
function,  768 
origin,   767 
pathology,   768 
physiology,  768 
Spinal  cord,  536 

anterior  median  groove,  538 

anterior   roots,    538,    605 

antero-posterior   lateral    grooves,    538 

blood-supply,  effect  of,  602 

centers  in,  608 

central  canal,   544 

columns  of,  545 

conduction  of,  603 

commissures  of,  550 

coverings  of,  537 

degenerations  of,  550 

diameter  of,  537 

ependyma,   544 

experiments  on,  606 

exterior  form,  538 

fibers  of,   541 

general  description  of,  538 

gray  commissure  of,  538 

gray  matter  of,  539 

Internal  conformation  of,  539 

length  of,  537 

minute  structure  of,  541 

neuroglia,  542 

path  of  motion  in,  605 

path  of  sensation  in,  605 

posterior  median  fissure,  538 

posterior  roots  of,   550,  605 

recurrent  sensibility  of,  604 


Si)inal  cord,  reflex  action  of,  600 
forms  of,  001 
laws  of,  601 
swiftness  of,  601 
skin  reflexes  in,  606 
suspension  of,  538 
systemization  of,   544 
tendon  reflexes  in,  607 
tonus  of,  602 
tracts,   comma,  549 
of  lateral  column,   547 
of  Lissauer,  549 
of  posterior  columns,  548 
trophic  centers  of,  536 
weight  of,  538 
^hite  commissure,  538 
Spinal  ganglion,  604 
Spirem,  20 
Spirits,   44 
Spleen,  364 

effect  of  injection  of  dried  extract,  365 

function  of,  364 

Malpighian  corpuscles  of,  304 

nervous  influences  of,  365 

pulp  of,  364 

structure  of,  364 

trabeculae,   364 
Spongioplasm,   9,  524 
Staircase  contraction,   244,   477 
Stammering,  500 
Stannius's  experiments,  231 
Stapes,   681 
Stapedius,  689 
Starch,  27 

Starling's  theory  of  lymph,   156 
Starvation,   effects  upon  proteid,   425 

description,  425 
Steapsin,  100 
Stearic  acid,  30 
Stearin,  30 
Stereognosis,  62C 
Stercobilin,  124 
Stethograph,   315 
Stilling,    raphe  of,   552 

canal  of,  716 
Stimulants  as  accessories,  43 
Stimulation  fatigue,  477 
Stimuli,   successive,   480 
Stokos-Adams  disease,  232 
Stomach,  66,  68 

absorption  from,   138 

action  of  agents  on,  78 

blood-supply  of,   68 

coats  of,   66 

glands  of,  68 

movements  of,  68 

mucous  membrane,  68 

nervous  control  of,  68 

Schuetz's  law,  73 

secretion   (see  gastric  juiee),  71 

secretory  nerves  of,  77 

structure  of,  66 
Stomata,   free,   148 
Strabismus,  738 
Stratum  complexium,  562 

corneum,  655 

granulosum,  655 

lucidum,   655 

profundum,  562 

zonale,  563 
Stromhur,    Ludwig's,   275 
Struggle  for  existence,  791 
Stuttering,   500 
Subarachnoidean  space,  537 
Subdural  space,  537 
Sublingual  glands,   55 
Submaxillary  ganglion,  763 
Substantia  gelatinosa  of  Rolando,  540 
Succi's  fast,  426 
Sugar  (see  dextrose). 


INDEX. 


813 


Succus  cntcricus,  121 

daily  secretion,  121 

ferments  of,   121,  122 

function   of,   121 

specific  gravity  of,  121 

sugar  in  urine,  412 
tests  for,   413 
Sulphur,  407 

Superior  laryngeal   nerve,   332,   496 
Superior   vermiform   process,   613 
Sulphuric  acid  in  urine,  407 
Superior  fovea,  562 
Suprarenal  capsules,  365 
Sustentacular  cells,  773 
Survival  of  the  fittest,  791 
Swallowing,   57,  58 
of  food,  57 
three  stages  of,  57 
of  fluids,  58 
mechanism   of,   58 
nervous  control  of,  59 
Sweat   (see  perspiration),  378 
Sweat  glands,  378 

experiments  on,  378 

nerves  of,  381 

number  of,  377 

structure  of,  378 
Sylvian  center,  450 
Sylvius,   fissure  of,  571 
Sympathetic,  the  great,  638 

afferent  fibers  of,  646 

efferent  fibers  of,  639 

ganglia  of,  639 
reflex  action  of,  649 

general   description   of,   639 

of  abdomen,   647 

of  arm,   648 

of  head  and  neck,  647 

of  leg,   648 

of  pelvis,   647 

of  thorax,  647 
Synthesis,  421 
Syntonin,  34 
Syringomyelia,  606 
Systemic  circulation,  211 
Systole  of  heart,  213 
Systolic  plateau,  220 

Tabes  dorsalis,  549 

Table  of  oxidation  in  starvation,   425,   426 

Tactile  sense,  653 

effect  of  liquids  on,  660 
effects  of  solids  on,  659 
cells,  606 

compound  sensations,  660 
illusions,  660 

knowledge  gained  from,  658 
law  of   Fechner,   653 
law  of  sensation,  653 
Taste,  665 
center  of,  626 
drugs,  668 

effect  of  drugs   on,  668 
general   description,   665 
improper  stimuli,  667 
intensity  of,  667 
nerves  of,   65,  666 
organs  of,  666 
substances  of,   668 
tongue's  part  in,    665 
Taste  buds,  667 
Taste  center,  626 
Taurocholic  acid,  110 
Tea,  44 

Tension,  arterial,  271 
Teeth,  49 
milk,  49 

number  of,  49,  50 
parts  of,  52 
permanent,  50 


Teeth,  structure  of,  52,  53 
Tegmentum,  566 
Teichmann's  crystals,  199 
Temperature,  437 

at  different  ages,  439 

cause  of  variations,  439 

estimation  of,  441 

extremes  of,  440 

modifying  influences,  439 

nerve-centers  of,  448 

of  animals,  437 
blood,  161,  440 
man,  437 

post  mortem,  455 

spots,  661 
Tendon  reflexes,  607 
Tendons  in  relation  to  muscle,  464 
Tenon's  capsule,  717 
Tensor  tympani  muscle,   692 
Tetanus  of  muscle,   482 
Tetany,  361 

Theory  of  preformation,  771 
Thermal  unit,  441 
Thermogenic  center,   447 
Thermoinhibitory  center,  449 
Thermolysis,  452 
Thermolytic  center,  450 
Thermotaxic  center,  447 
Thirst,  128 

Thoma-Zeiss  apparatus,  167 
Thoracic   duct,   146 
Thymus  gland,  370 

chemical  composition,  371 
extract  of,   371 
function  of,  371 
results  of  extirpation  of,  371 
structure,   371 
Thyro-arytenoideus  muscle,  495 
Thyroid  gland,   357 
function  of,  359 
internal  secretion  of,  362 
lymphatics  of,  358 
relation  to  heart,  363 
results  of  extirpation  of,  361 
structure  of,  358 
vessels  and  nerves  of,  358 
Tidal  air,  319 
Timbre  of  voice,  498 
Tissues,  6 

definition  of,  6,  17 
Tone,   491 
Tongue,  47 

in  deglutition,  57 

in  mastication,  56 

mucous  membrane,  49 

nerves  of,  49 
Tonicity,  483 
Touch,  653 
Touch  center,  630 
Touch  corpuscles,  656 
Toxalbumin,  291 
Toxproteins,  291 
Toxins,  291 
Trachea,  302 

Transitional  leucocytes,  172 
Trapezoid  body,  562 
Traube-Hering  curves,  272 
Transfusion,  197 
Tricuspid  valve,   206 
Trifacial,  756 

distribution  of,  759 

function  of,   759 

irritation  of,  761 

motor  function  of,  761 

origin,   759 

pathology  of,   761 

physiology   of,    759 

reflex  actions  of,  331,  760 

trophic  function  of,   761 
Trigonum  acustici,  556 


814 


INDEX. 


Trigonum  hypoglossi,  556 
Trigonuni  vagi,  556 
Trochlear  nerve,  753 
Trophoblast,  780 
Trophic  centers,  447 
Trypsin,   99,   103 
Trypsinogen,  95 
Tryptophan,   32 
Tube  casts,  413 
Tuber   cinereum,   449 
Tiirck's  tract,   545 
Tympanum,   G79 

mucous  membrane  of,   G79 
Trypsin,   95 
Tyrotoxicon,  42 


Units   of   measurement,   Ml 
Uffelmann's   test   for    lactic   acid,    83 
Uhlenhuth's  test  for  blo6d,   294 
Urates,  409 
Uraemia,  415 
Urea,  395 
crystals  of,   395 
decomposition  of,  395 
excretion  of  muscular  labor,   396 
formation  of,  397 
properties  of,  395 
quantity  of,  396 
Ureters,  416 
Uric  acid,  398 

daily  amount  of,  400 
formation  of,  399 
increased  by  food,  399 
murexide  test  for,  401 
quantity  of,  400 
tests,   401 
Uric  sediments,   409 
Urinary  apparatus,   415 
Urinary  bladder,  417 

blood,  nerve,   lymph  supply  of,  385 
capacity  of,   385 
structure  of,  417 
Urinary  tubules,  389 
Urine,   393 
acidity  of,  394 
albumin  in,  411 
Heller's   nitric   acid   test,    411 
bile  pigments  of,  406 
coloring  matters  of,   404 
oomposition  of,  407 
drug  pigments  of,  406 
fermentation  of,  407 
inorganic  constituents,  406 
movements  of,  416 
nerves,  influence  of  on,   415 
pathological  pigments,   405 
quantity  of,   393 
reaction  of,   393 
secretion  of,  414 
sediments  of,  410 
oxalic  acid,   409 
phosphorus,   410 
specific   gravity  of,   394 
sugar  in,  412 

Pehling's  test,  412 
fermentation  test  for,   413 
phenylhydrazin  test  for,   413 
temperature  of,   393 
tides,  394 

theory  of  secretion  of,  413 
toxicity  of,  414 
tube  casts,  413 
Urobilin,   404 
Urochrome,  404 
Uroerythrin,  404 
Uterus,  788 

secretion,  787 
Utricle,  698 


Vagina,  788 
Vagus,  234 

accelerator  fibers,   241 

depressor  fibers,  238 

effect    of    division    of    accelerator    fibers, 
241 

effect  of  irritation  of  accelerator  fibers, 
241 

effect  of  section  of,  237,  331 

effect  of  sipping  upon,  236 

effect  of  stimulation  of,  235 

effect  of  swallowing  liquids  upon,  236 

peculiarities  of,   235 

pneumonia,   331 

relation   to   blood-pressure,   272 
Valves  of  heart,  207 
Valvules  conniventes,   86 
Variation,  791 
Vasa  vasorum,   247 
Vasoconstrictors,  281 

effect  of  irritation  of,  282 
effect  of  section   of,   281 

differences  from  vasodilators,   285 

of  abdominal  viscera,   283 

of  extremities,   283 

of  head,    282 

of  lungs,  284 
Vasodilators,  284 

path  of,  285 

recognition  of,  285 

theory  of  action  of,  286 
Vasomotor  nerves,  280 

effect  of  section  of,  281 
effect  of  stimulation   of,   282 
pathologic  conditions  of,  290 
Vasomotor  system,  279 
centers  of,   286 
function   of,   288 
nerves  of,   280 
reflexes  of,  288 
Vegetable  cell,  6 
Vegetable  foods,  42 
Veins,   247 

blood-pressure  in,  273 

coats  of,   247 

lymph  and  nerve  supply,  248 

portal   vein,   106 

rate  of  blood  in,   276 

tension  in,  273 

valves   of,   248 

vasa  vasorum  of,  248 
Venom,   266 
Venous  blood,  163 
Venous  circulation,  277 
Venous  pulse,   273 
Ventilation,  353 
Ventricles  of  larynx,  493 
Ventricles  of  heart,  211 
Ventriloquy,    499 
Vermis,  620 

Vesicospinal  centers,   418 
Vessel  innervation,  advantages  of,  288 
Vestibular  nerve,  687 
Vestibular  nucleus,   687 
Vestibule,  683 
Vestibulo-spinal  tract,  548 
Vibrations   in  car,   694 
Villi,    86,    149 

epithelial  cells  of,   87 

goblet  cells  of,  87 

of  intestines,  86 

structure  of,  87,  88 
Vision,   accommodation,   722 

acuteness  of,  728 

after-images,  738 

aqueous  humor,  716 

astigmatism,  726 

binocular  vision,  739 

center  of,  627 

chromatic   aberration,   722 


INDEX. 


815 


Vision,  color  vision,  735 
complementary  colors,   735 
crystalline  lens,   709 
Daltonism,  735 
dioptrics,   721 
hypormetropia,  724 
irradiation,   736 
lacrymal  secretion,  742 
lenses,   726 
lymphatics,  718 
movements  of  eyes,  710 
myopia,  724 
oplithalmoscope,  742 
optic  nerve,  713 
perception  of  light,  720 
perimeter,   743 
phosphenes,  737 
presbyopia,   724 
retina,   710 

retinal  epithelium,  713 
rhodopsin,  713,  732 
sensation  of  color,  734 
Snellen's   test-types,   731 
spherical   aberration,   722 
transmission  of  light,  699 
visual  angle,  370 

apparatus  (see  eye), 
structure  of,  700 

purple,   713 

area,  743 

field,  746 

line,  730 
Vital  capacity,  319 
Vitelliu,   39 
Vitreous  humor,  716 
Vocal  cords,  493,  496 

conditions   of,   496 

false,  493 

true,  493 
Voice  and  speech,  497 

height  of,  497 

organ   of,    496 

range  of,  498 


Vomiting,  83 

causes,   84,   621 

mechanism  of,  83,  84 

nerve  center,  84 
Von  Bezold's  ganglion,  232 
Vowels  and  consonants,  499 

Wallerian  degeneration,  604 
Warm-blooded  animals,  437 
Water,  26 

daily  amount,  26 

drinking,  26 

in  faeces,  125 

in  metabolism,   428 
Weber's  schema  of  circulation,  251 
Wheat,   43 
Whey,  41 

Widal  reaction,  294 
White  columns, -545 
White    corpuscles    (see    blood-corpuscles), 

170 
Wine,    44 

Wing  muscles  of  insect,  461 
Wirsung's  duct,  94 
Word-centers,  501,  627 
auditory,  501,  626 
visual.   .500,   626 
Work,   effect  upon   destruction   of  proteid, 

474 
Wrisberg's  cartilages,  493 

Xanthin  in  urine,  402 
Xanthoproteic  test  for  proteids,  35 

Yawn,  339 


Zonule  of  Zian,  723 
Zymogen,  95 
Zymoids,   291 


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